energy Archives - Formula Health

27/Sep/2026

Walking into a room and forgetting why. Losing the thread mid-sentence. Reading the same paragraph three times. Feeling slower than you were previously, then being told that your blood tests are normal.

Brain fog describes a cluster of cognitive symptoms rather than a single diagnosis.

Brain fog is not a diagnosis. It is a colloquial, non-medical term describing difficulties with attention, memory, concentration, word-finding, planning, multitasking and mental energy. It is a transdiagnostic symptom cluster reported in perimenopause, thyroid disease, iron deficiency, vitamin B12 deficiency, insulin resistance, sleep disorders, long COVID, mood disorders and following chemotherapy.[1][2][3]

That breadth is precisely why the investigation must be systematic. A standard panel can exclude some serious conditions while failing to explain why you feel cognitively slowed.

1. Ferritin and iron status

Iron deficiency can affect cognition before anaemia develops. A normal haemoglobin result does not confirm adequate iron availability for the brain, muscles or neurotransmitter pathways.

Ferritin below approximately 30 µg/L is commonly interpreted as depleted iron stores in an appropriate clinical context. Inflammation can raise ferritin and obscure deficiency, making transferrin saturation and inflammatory markers relevant.[4]

Marker	Conventional interpretation	Why context matters	A more informative approach
Ferritin	Iron stores appear adequate if within the laboratory range	Laboratory reference ranges may include levels associated with symptoms; inflammation can falsely elevate ferritin	Interpret with full blood count, transferrin saturation and CRP. Review menstrual loss, diet and gastrointestinal symptoms
Haemoglobin	Anaemia is absent if normal	Iron deficiency without anaemia can still contribute to fatigue, poor concentration and cognitive slowing	Do not use haemoglobin alone to assess iron status

Read the detailed guide to iron deficiency without anaemia and ferritin.

2. Active B12, folate and homocysteine

Total serum B12 can appear normal or high despite impaired cellular availability. This is particularly relevant following supplementation, with altered binding proteins, or where absorption is compromised.

Methylmalonic acid (MMA) and homocysteine can provide additional information when symptoms are significant but serum B12 is not clearly deficient. MMA is more specific to B12 status, although renal impairment can affect interpretation. Homocysteine may rise with B12, folate or vitamin B6 deficiency and is not specific to one nutrient.[5]

Marker	Conventional interpretation	Why context matters	A more informative approach
Total serum B12	B12 deficiency is unlikely if the result is in range	Serum concentration does not always reflect tissue-level function	Consider active B12 with MMA and homocysteine when symptoms or risk factors persist
Folate	Folate status is adequate if serum folate is normal	Folate and B12 deficiency can overlap and both affect one-carbon metabolism	Interpret with B12, homocysteine, diet and absorption history
Homocysteine	Raised homocysteine is non-specific	It may reflect B12, folate or B6 deficiency, renal impairment and other factors	Use as part of a marker pattern rather than in isolation
MMA	Raised MMA suggests cellular B12 deficiency	Renal function and some analytical factors influence the result	Interpret alongside B12, active B12 and renal markers

See the companion articles on the active B12 test and cellular deficiency and homocysteine and brain fog.

3. A full thyroid assessment, not TSH alone

TSH is an important first-line thyroid marker. It does not, however, describe every aspect of thyroid physiology or autoimmune activity.

Depending on the clinical picture, a fuller assessment may include free T4, free T3, thyroid peroxidase antibodies and thyroglobulin antibodies. Iron status also interacts with thyroid hormone production and metabolism. Low iron stores can therefore complicate the interpretation of fatigue, cold intolerance and cognitive slowing.[6]

Marker	Conventional interpretation	Why context matters	A more informative approach
TSH	Primary screening marker for thyroid dysfunction	A single result may not explain symptoms, treatment effects or autoimmune activity	Interpret with free T4 and the clinical picture
Free T4 and free T3	Circulating thyroid hormones	Results may be affected by illness, medication, nutritional status and assay variation	Review alongside TSH, symptoms and iron status
TPO and thyroglobulin antibodies	Evidence of thyroid autoimmunity	Antibodies can be present before overt thyroid dysfunction	Consider where autoimmune thyroid disease is suspected

Thyroid testing sidebar: reverse T3
Reverse T3 (rT3) is an inactive metabolite of thyroid hormone. The claim that rT3 blocks thyroid hormone receptors is not supported by adequate evidence. rT3 testing is not recommended as a routine thyroid assessment by professional guidance, including the American Thyroid Association. It should not replace evidence-based thyroid evaluation.[7]

Read why TSH alone may not be enough.

4. Fasting insulin and HOMA-IR

Glucose and HbA1c can remain within range while insulin resistance is developing. Higher insulin requirements and substantial post-meal glucose variation may affect energy, attention and perceived mental clarity before conventional glucose markers change.

Fasting insulin, interpreted with fasting glucose, can be used to calculate HOMA-IR. This is not a standalone diagnosis. It is a context-dependent estimate of insulin resistance that must be considered alongside waist circumference, blood pressure, lipids, PCOS, family history and medication.[8]

See the guide to fasting insulin and HOMA-IR.

5. Vitamin D

Vitamin D thresholds are primarily established around bone health. They do not necessarily define the concentration associated with optimal energy, immune or neurological function.

Low vitamin D may coexist with fatigue, musculoskeletal symptoms and reduced wellbeing. The result should be interpreted with season, sun exposure, skin pigmentation, body composition, diet and clinical history. Supplementation should be appropriate to the result rather than added indiscriminately.[3][9]

6. Magnesium and other micronutrients

Most magnesium is stored in bone and tissue. Serum magnesium represents only a small extracellular compartment and is tightly regulated. A normal serum result therefore does not always exclude suboptimal total-body status, although this does not justify diagnosing deficiency from symptoms alone.[10]

Marker	Conventional interpretation	Why context matters	A more informative approach
Serum magnesium	Magnesium status is adequate if serum magnesium is normal	Serum magnesium may remain normal despite depleted tissue stores	Interpret with diet, gastrointestinal health, kidney function, medication and symptoms
Zinc, copper and selected micronutrients	Not usually included in a standard panel	Restrictive diets, malabsorption and chronic gastrointestinal disease can alter status	Test selectively when the history creates a clinical question
CRP and related inflammatory markers	Inflammation is absent if CRP is normal	Some inflammatory processes fluctuate or are not captured by one test	Repeat or broaden assessment only when the clinical picture warrants it

Read the companion article on what a normal serum magnesium result may miss.

7. Sex hormones and the perimenopause

More than two-thirds of women report cognitive symptoms such as forgetfulness, word-finding difficulty or reduced concentration during the menopause transition.[11] The experience is real, although routine hormone blood tests do not always identify the cause because oestrogen and progesterone fluctuate substantially during perimenopause.

Oestrogen is not solely a reproductive hormone. It influences brain networks involved in attention, memory, mood, sleep and thermoregulation. Falling or fluctuating oestrogen can coincide with hot flushes, night sweats, sleep fragmentation, anxiety and changes in cognitive confidence.[11][12]

The cortisol awakening response is also relevant to sleep and stress physiology. It is not a universal screening test for brain fog, but disrupted sleep timing, prolonged stress and altered morning alertness can materially influence cognition.

Marker	Conventional interpretation	Why context matters	A more informative approach
Oestradiol, FSH and LH	Used to assess reproductive hormone status	Perimenopausal levels fluctuate and a single sample may be misleading	Prioritise symptom pattern, cycle history, age and clinical assessment
SHBG and testosterone	Often associated mainly with libido	Testosterone has roles in energy, muscle, mood, cognition and bone health in women, not libido alone	Interpret with symptoms, SHBG and the wider hormonal picture
Cortisol	A single cortisol result is often over-interpreted	Cortisol follows a circadian rhythm and is affected by sleep, illness and medication	Assess sleep timing, stress physiology and clinical context before considering specialised testing

Read about hormone blood tests and SHBG, oestrogen, menopause and the brain-body connection, and the cortisol awakening response.

Brain fog can be subjective and still clinically important

A 2025 systematic review and meta-analysis of 24 studies involving 5,629 participants found that the overall association between subjective cognitive complaints and objective cognitive performance during menopause was not statistically significant. A small association was identified specifically for learning efficiency.[13]

This does not invalidate the symptom. It means that self-reported cognitive difficulty and performance on formal neuropsychological tests measure related but different experiences. Sleep disruption, vasomotor symptoms, mood, stress and hormonal change may affect how a person functions day to day without producing a clear abnormality on a brief test.[11][12]

Being told that your tests are normal is not the same as being told that nothing is wrong.

Brain fog is a real experience, even when standard blood tests do not explain it.

Long COVID and chemotherapy-related cognitive symptoms

Brain fog is reported in approximately 20–30% of people with long COVID, with estimates varying according to the population and definition used. Proposed mechanisms include neuroinflammation, immune dysregulation, microvascular injury, metabolic dysfunction and disruption of the gut-brain axis.[2][3]

A 2025 transdiagnostic review argues that brain fog is a genuine and measurable clinical phenomenon, but one that lacks a standardised definition.[1] Similar cognitive symptoms occur following chemotherapy. A systematic review in breast cancer survivors found self-reported cognitive impairment in approximately 44%, while objective impairment varied by assessment method and was generally lower.[14]

These figures demonstrate why symptoms should be assessed rather than dismissed. They do not identify one universal treatment.

What standard panels commonly miss

When routine results do not explain the presentation, clinicians should also consider:

Sleep apnoea, insomnia and fragmented sleep.
Mood and anxiety disorders, including symptoms that present primarily as poor concentration.
Coeliac disease and other causes of malabsorption.
Chronic inflammation, autoimmune disease or persistent infection where clinically indicated.
Perimenopause, particularly when sleep, cycle, vasomotor and mood symptoms occur together.
Medication effects, alcohol use, overtraining and inadequate energy intake.

A realistic investigation is prioritised, not indiscriminate. When energy and budget are limited, one or two well-chosen markers linked to the clinical question can provide more useful information than a comprehensive panel ordered without a clear rationale.

A practical order of investigation

Clarify the pattern. Record onset, fluctuations, sleep, menstrual or menopausal symptoms, diet, medication, alcohol, infections and neurological symptoms.
Start with high-yield basics. Consider full blood count, ferritin and iron studies, thyroid assessment, B12-related markers and glucose regulation according to history.
Add targeted tests. Consider vitamin D, magnesium, coeliac screening, inflammatory markers, sex hormones or further metabolic markers where the presentation supports them.
Correct identified deficiencies properly. Confirm the likely cause, use appropriate treatment and reassess rather than adding multiple supplements simultaneously.
Protect sleep first. The highest-yield modification for many people is consistent sleep timing and sufficient duration. Reduce alcohol, build protein and glucose stability into breakfast, and change one variable at a time.
Escalate when necessary. Persistent symptoms may require sleep assessment, psychological support, neurological assessment or review of medications.

Formula Health provides a 90-minute initial consultation and 60-minute follow-ups, supported by a joined-up multidisciplinary team: your health pitstop crew. The practice was founded by Gemma Fisher, the first Human Performance Consultant Osteopath in Formula 1, bringing elite-performance insight to personalised healthcare. Explore the Formula Health services.

When brain fog requires prompt assessment

Brain fog can occasionally be an early sign of a condition requiring urgent investigation. Seek prompt medical attention for rapidly progressive cognitive change, acute confusion, new weakness, facial drooping, speech disturbance, severe headache, seizure, loss of balance or other neurological findings.

References

Denno A, Hampshire A. Defining Brain Fog: A Transdiagnostic Narrative Review. European Psychiatry. 2025.
Systematic review and meta-analysis of long COVID mental health conditions and brain fog.
Nutritional approaches to brain fog, neuroinflammation, the gut-brain axis and sleep. Current Nutrition Reports. 2026.
Iron deficiency without anaemia: indications for treatment.
Active B12, homocysteine and functional B12 assessment.
Thyroid testing and the limitations of TSH alone.
American Thyroid Association guidance and thyroid testing principles. American Thyroid Association.
Fasting insulin and HOMA-IR in early metabolic risk.
Vitamin D thresholds and energy function.
Normal serum magnesium and potential limitations of blood testing.
Gurvich C, et al. Cognitive symptoms during menopause. The Lancet.
Maki PM, Jaff NG. Brain fog in menopause: an IMS White Paper. Climacteric. 2022.
Furey RT, Thomas EHX, Kulkarni J, Gurvich C. Subjective versus objective cognition during menopause: a systematic review and meta-analysis. Journal of the International Neuropsychological Society. 2025.
Whittaker AL, et al. A systematic review and meta-analysis of cognitive impairment following chemotherapy in breast cancer. Scientific Reports. 2022.
Homocysteine: the marker behind fatigue, brain fog and heart risk

Continue reading

Medical disclaimer: This article is for general information and does not replace an individual medical assessment, diagnosis or treatment plan. Test selection and interpretation should be based on your symptoms, history, examination and existing results. Seek urgent medical attention for acute confusion, rapidly progressive cognitive change or neurological symptoms.

Gemma Fisher

23/Sep/2026

You sleep for a full night, yet wake feeling depleted. Energy never fully arrives. Caffeine becomes essential rather than optional. Exercise tolerance declines. Concentration becomes inconsistent. Your blood tests return as “normal”, but you do not feel well.

“Normal” and “optimal” are not interchangeable. Laboratory reference intervals are generally calculated from the central 95 per cent of a selected population. They are designed primarily to identify established disease, not to confirm optimal physiological function. The reference population may also include people with undiagnosed nutrient deficiency, chronic inflammation or early disease.

Persistent fatigue requires a structured assessment of patterns. Iron, ferritin and vitamin B12 are important, but they are not the only biomarkers capable of explaining why someone wakes with an empty tank.

“Normal” is not necessarily optimal

A reference interval describes how a particular group tested at a particular laboratory using a particular assay. It does not define the level at which every individual functions best.

Marker	Conventional interpretation	Why context matters	A more informative approach
Ferritin	Often flagged low below 15–30 µg/L	Inflammation can raise ferritin and conceal iron deficiency	Assess ferritin with transferrin saturation, CRP and the full blood count.
Vitamin B12	Total serum B12 within the laboratory range	Total B12 can be misleading when functional markers are abnormal	Measure active B12, methylmalonic acid, folate and homocysteine for a clearer cellular picture.
TSH	Usually approximately 0.4–4.0 mIU/L	Antibodies, free T4, symptoms and trends affect interpretation	Interpret with free T4, thyroid antibodies and the trend over time, not a single TSH value.
Vitamin D	UK deficiency risk below 25 nmol/L	Some clinical frameworks consider 25–50 nmol/L insufficient	Interpret 25-hydroxyvitamin D against symptoms, sun exposure, supplementation and musculoskeletal findings.
Fasting insulin	Often reported within a broad laboratory interval	Rising insulin may precede abnormal glucose or HbA1c	Calculate HOMA-IR from a properly fasted sample with fasting glucose, HbA1c, triglycerides and HDL.
Magnesium	Serum magnesium within the laboratory range	Serum magnesium represents only a small, tightly regulated compartment	Assess with symptoms, medication, kidney function, diet and gastrointestinal history; red-cell magnesium is not standardised.

The appropriate question is not simply whether a result is inside the printed range. It is whether the result is clinically coherent with the symptoms, history and other biomarkers.

Ferritin: why women can be iron deficient without anaemia

Iron deficiency is not synonymous with iron-deficiency anaemia. Iron stores can become depleted while haemoglobin remains within range.

Symptoms of depleted iron stores can include:

Persistent fatigue and unrefreshing sleep.
Reduced exercise tolerance.
Breathlessness on exertion.
Hair thinning.
Restless legs.
Palpitations.
Cold intolerance.
Brain fog.
Pica, including cravings for ice or non-food substances.

A normal full blood count does not exclude iron deficiency without anaemia. Ferritin and transferrin saturation are required to assess iron availability more accurately.

Why sex-specific ferritin ranges are under scrutiny

Ferritin reference intervals were not simply built from male data. Historically, they were derived from general population samples that included people with undiagnosed iron deficiency.

Because iron deficiency is substantially more prevalent in menstruating women, female reference intervals were often set lower than male intervals. Leading haematologists argue that this difference may reflect statistical normalisation of a disease state rather than a genuine physiological distinction.

The 2024 systematic review in The Lancet Haematology found that ferritin lower limits in published reference intervals were consistently below 30 µg/L. The median lower limit was approximately 8 µg/L for females and 25 µg/L for males. The authors concluded that many existing intervals are too low to identify iron deficiency reliably. [1]

There is no single standardised UK ferritin reference range. Intervals vary between laboratories, assays and populations. The same result can therefore be marked as normal at one laboratory and low at another. [2]

Conventional versus emerging clinical thresholds

Clinical context	Ferritin interpretation
Conventional definition	Below 15 µg/L is traditionally used to define iron deficiency
General adult threshold in newer guidance	30 µg/L or lower
Menstruating individuals	30 µg/L or lower
Heavy menstrual bleeding or other high-risk situations	50 µg/L or lower may support diagnosis
Inflammation or anaemia of inflammation	Ferritin below 100 µg/L or transferrin saturation below 20 per cent may indicate deficiency

The 2026 American Society of Hematology guidance recommends a ferritin threshold of 30 µg/L or lower for adults, including menstruating individuals. It supports a threshold of 50 µg/L or lower in high-risk groups, such as people with heavy menstrual bleeding. Where inflammation is present, ferritin below 100 µg/L or transferrin saturation below 20 per cent supports iron deficiency. [3]

This represents an important upward movement from the conventional 15 µg/L threshold. Women previously told that their iron was “normal” may fall into a deficient category when assessed using newer clinical decision limits.

Ferritin is also an acute-phase reactant. Infection, inflammation and liver disease can raise ferritin independently of iron stores. A full blood count, transferrin saturation and CRP are therefore important when ferritin does not match the clinical picture.

Iron deficiency without anaemia is clinically significant. A 2017 meta-analysis of randomised trials found that iron treatment reduced subjective fatigue in adults with iron deficiency without anaemia, with a pooled effect size of 0.33. A 2018 systematic review of randomised trials reached a similar conclusion, particularly in people with low or borderline ferritin. [4,5]

The 2025 CMAJ review recommends assessing ferritin alongside the full blood count and considering transferrin saturation where inflammation is present. The cause must also be investigated. Heavy menstrual bleeding, coeliac disease, restrictive diets, gastrointestinal blood loss, malabsorption and frequent blood donation are relevant possibilities. [6]

Vitamin B12 and folate: the test that can look fine while you are depleted

Total serum B12 measures circulating cobalamin bound to different proteins. It does not necessarily reflect the amount available to cells.

A high or apparently adequate B12 result can be misleading in the presence of:

Supplementation.
Liver disease.
Inflammation or malignancy.
Assay interference.
Macro-B12, where B12 is associated with immunoglobulins and binding proteins.

This does not mean that every high B12 result represents deficiency. It means that total B12 should not be interpreted in isolation when symptoms or other findings raise clinical suspicion. [7,8]

More functional assessment can include:

Methylmalonic acid (MMA): a sensitive marker of intracellular B12 function.
Total homocysteine: rises with B12 or folate deficiency, although it is less specific.
Holotranscobalamin: the fraction of B12 available for cellular uptake.
Combined B12 indicator (cB12): a composite measure incorporating several B12-related biomarkers.

MMA and homocysteine can also rise with renal impairment, age and other nutrient deficiencies. Interpretation requires clinical context, renal function and folate status. [9]

B12 and folate deficiency can contribute to fatigue, cognitive symptoms, low mood, neuropathy and other neurological features. Risk is increased with long-term metformin, proton pump inhibitors, H2 blockers, vegan or vegetarian diets, previous bariatric surgery, malabsorption and pernicious anaemia.

Homocysteine: a functional marker of B-vitamin status

Homocysteine is an amino acid intermediate in one-carbon metabolism. Its clearance depends on vitamin B12, folate and vitamin B6.

A raised result can prompt assessment of:

B12 deficiency.
Folate deficiency.
B6 deficiency.
Renal impairment.
Hypothyroidism.
Malabsorption.
Relevant medication use.
MTHFR variants, where clinically appropriate.

Homocysteine is associated with cardiovascular and cognitive risk, but association does not prove causation. B-vitamin supplementation lowers homocysteine, yet large trials have not consistently demonstrated a reduction in overall cardiovascular events. It should therefore be used to investigate a clinical pattern, not as a standalone cardiovascular screening test. [10]

Thyroid: why TSH alone is not the whole picture

Most UK laboratories use an adult TSH reference interval of approximately 0.4–4.0 mIU/L, although the exact range varies.

Some endocrinologists argue that a narrower upper limit of approximately 2.5 mIU/L better reflects a rigorously thyroid-healthy, antibody-negative population. Others warn that applying this threshold universally could overdiagnose and overtreat people with normal thyroid function.

A meaningful thyroid assessment may include:

TSH.
Free T4.
Free T3, where clinically indicated.
Thyroid peroxidase antibodies.
Thyroglobulin antibodies.

Positive antibodies can identify autoimmune thyroid disease and increase the risk of future hypothyroidism, even when TSH remains within range. Free T3 may provide additional context, but its role in diagnosing hypothyroidism remains debated. Levels often remain within range when TSH is abnormal, and measurement is less robust than free T4. [11,12]

Iron and thyroid physiology are also interdependent. Thyroid peroxidase is a haem-containing enzyme, and iron deficiency can compound symptoms associated with reduced thyroid function. Low ferritin can therefore be relevant when fatigue persists despite apparently reassuring thyroid results.

Reverse T3: why it is not the answer you may have been told it is

Sidebar: Reverse T3 (rT3) is an inactive metabolite of T4. It is produced when deiodinase enzymes redirect T4 away from active T3 production, particularly during illness, physiological stress and starvation. This is generally understood as an energy-conserving adaptation rather than a disease process in its own right. A widely promoted claim is that rT3 “blocks” T3 at the receptor and causes hormone “pooling”. That proposition does not hold up well against the evidence. rT3 does not bind nuclear thyroid hormone receptors and, in normal subjects, does not appear to alter pituitary-thyroid function. Current evidence does not support using rT3 to diagnose hypothyroidism or to guide T4 or T3 prescribing. The 2023 American Thyroid Association-commissioned review concluded that rT3 is rarely useful in routine practice, with legitimate exceptions largely limited to rare genetic thyroid syndromes and consumptive hypothyroidism caused by unusual tumours. It is not recommended by professional practice guidelines, and assay agreement between platforms is poor. This matters because rT3-led decision-making often pushes patients towards excessive thyroid hormone doses, which carry real risk. Many women are told that rT3 is the marker their GP will not run. Our preference is to interrogate ferritin and iron status, thyroid antibodies, free T4, the TSH trend over time, symptoms, and the drug and supplement history instead. [13,14]

Fasting insulin and HOMA-IR: metabolic dysfunction before abnormal glucose

Glucose and HbA1c can remain within range while insulin is rising. The pancreas can compensate for declining insulin sensitivity by producing more insulin, maintaining normal glucose for a period of time.

Fasting insulin and HOMA-IR can help identify this earlier pattern.

HOMA-IR is calculated from fasting glucose and fasting insulin:

HOMA-IR = fasting insulin × fasting glucose ÷ 22.5

Published thresholds vary substantially. A Brazilian laboratory proposal reported a 95 per cent reference interval of approximately 2.52–13.14 µU/mL for fasting insulin and 0.39–2.86 for HOMA-IR. A prospective Chinese cohort identified cut-offs of approximately 1.4 for dysglycaemia and 2.0 for type 2 diabetes risk. A value of 2.5 is commonly used in US research as a marker of insulin resistance. These thresholds are population-specific, not universal diagnostic boundaries. [15–17]

The symptom pattern can include:

Central weight gain.
Post-meal energy crashes.
Sugar or carbohydrate cravings.
Night waking.
Difficulty changing body composition despite training.
Reduced recovery.
Increasing fatigue after exercise.

Perimenopause and menopause can alter sleep, body composition and insulin sensitivity. Fasting insulin is therefore relevant to women over 40, particularly when glucose and HbA1c appear reassuring.

Vitamin D: a threshold established primarily for bones

Current UK guidance identifies serum 25-hydroxyvitamin D below 25 nmol/L as the level at which the risk of deficiency and poor musculoskeletal health increases. Levels between 25 and 50 nmol/L are commonly described as insufficient in NHS clinical guidance, while levels above 50 nmol/L are often considered sufficient.

SACN established the 25 nmol/L threshold primarily for population-level musculoskeletal protection. It was not designed to define an optimal energy level.

A 2026 Frontiers in Endocrinology commentary calls for the UK threshold to be reconsidered and proposes 50 nmol/L as a more clinically meaningful deficiency threshold. This is a recommendation for policy change, not an implemented national redefinition. [18,19]

Vitamin D deficiency can contribute to muscle weakness, reduced physical function and fatigue. Limited cutaneous synthesis between October and March makes low levels common in the UK. Sunbeds are not a safe solution.

Magnesium: why a normal serum result may not be reassuring

Less than 1 per cent of total body magnesium is present in the blood. Serum magnesium is tightly regulated by renal and bone mechanisms, so intracellular depletion can exist alongside a normal serum result.

Symptoms and risk factors may include:

Fatigue.
Muscle cramps.
Poor sleep.
Palpitations.
Tension headaches.
Long-term proton pump inhibitor use.
Diuretic use.
Alcohol excess.
Diabetes.
Gastrointestinal disease or malabsorption.

Red-cell magnesium may provide additional information about intracellular stores, but its clinical utility remains debated. Methods and reference intervals are not sufficiently standardised for universal interpretation.

Some researchers propose 0.85 mmol/L as a more clinically useful lower threshold for serum magnesium. This is not yet a universally accepted diagnostic cut-off. Magnesium should be interpreted alongside symptoms, medication, kidney function, diet and gastrointestinal history. [20–22]

Cortisol and the cortisol awakening response

The cortisol awakening response is the normal rise in cortisol during the first 30–45 minutes after waking. It contributes to morning alertness and physiological readiness.

Perimenopausal vasomotor symptoms and sleep fragmentation can affect cortisol rhythms. In a 2023 experimental model of menopause, sleep fragmentation increased bedtime cortisol by approximately 27 per cent and reduced the cortisol awakening response by approximately 57 per cent. Estradiol suppression alone did not significantly alter the awakening response. [23]

This supports a clinically important distinction: waking empty may reflect fragmented sleep and altered stress physiology rather than insufficient time in bed.

Cortisol awakening response testing is not a routine diagnostic test for fatigue or menopause. Salivary cortisol patterns require careful collection and clinical interpretation. A single cortisol value cannot diagnose “adrenal fatigue”.

Sex hormones, SHBG and what not to test routinely

Oestradiol, FSH, LH, testosterone and SHBG can be relevant in selected cases. Testosterone should not be interpreted without SHBG and appropriate clinical context.

The interpretation depends on:

Menstrual cycle stage.
Contraception.
HRT.
Symptoms.
Age.
Pregnancy status.
Suspected premature ovarian insufficiency.

NICE states that women aged 45 and over with typical menopausal symptoms are generally diagnosed clinically rather than through routine hormone testing. FSH may be appropriate between 40 and 45 where menopause is suspected, or under 40 where premature ovarian insufficiency is being assessed. Hormone testing is not routinely required to monitor HRT. [24,25]

This is why comprehensive testing should be targeted rather than indiscriminate.

Markers that are often missed

Depending on the clinical picture, additional tests may include:

Full blood count and blood film: anaemia, red-cell abnormalities and other haematological patterns.
CRP or high-sensitivity CRP: inflammation affecting ferritin and broader interpretation.
Coeliac serology: a commonly missed cause of iron and B-vitamin malabsorption.
Vitamin B6: relevant to homocysteine metabolism.
Renal and liver function: affects MMA, homocysteine, ferritin and magnesium interpretation.
Fasting lipids: triglycerides and HDL add context to insulin resistance.
Gut health markers: only where clinically indicated and interpreted appropriately.

Patterns matter more than single numbers

Functional medicine uses a pattern-based approach. It does not mean treating every borderline result or pursuing an unlimited list of tests.

Useful patterns can include:

Low ferritin alongside reduced exercise tolerance and heavy menstrual bleeding.
B12 or folate insufficiency with raised homocysteine.
High-normal fasting insulin with post-meal crashes, increased triglycerides and reduced recovery.
Positive thyroid antibodies with rising TSH and low-normal free T4.
Low vitamin D with muscle weakness and reduced physical function.
Sleep fragmentation with a flattened morning cortisol response.
Gastrointestinal symptoms alongside recurrent iron or B-vitamin deficiency.

Trends, ratios and interactions can be more informative than one isolated result.

A realistic approach when you cannot do everything

Start with a baseline assessment. Persistent fatigue usually warrants more than a full blood count alone. Ferritin, transferrin saturation, B12, folate, thyroid markers, vitamin D, renal function, liver function, CRP, glucose and HbA1c may be considered according to the clinical history.
Test appropriately. Fasting insulin requires a fasting sample. Hormone results must be timed appropriately where cycle stage is relevant. Always disclose supplements and medication.
Correct likely contributors first. Iron, B12 or folate deficiency, vitamin D deficiency and thyroid dysfunction should be assessed and managed before pursuing less established explanations.
Make one meaningful change at a time. This makes symptom response and retesting easier to interpret.
Retest at an appropriate interval. Three to six months is reasonable for many nutritional and metabolic trends, although anaemia or significant deficiency may require earlier clinical review.
Do not start iron without appropriate assessment. Ferritin, transferrin saturation and the underlying cause of deficiency should be considered before supplementation. Iron can be harmful when taken unnecessarily.

What happens at Formula Health?

Formula Health provides an award-winning, multidisciplinary approach to personalised healthcare.

The process begins with a 90-minute consultation covering your symptoms, menstrual and hormonal history, medication, training load, sleep, diet and previous results. Blood testing is targeted to the clinical picture rather than delivered as a one-size-fits-all panel.

Results are interpreted in context. The women’s health, nutrition, medical and performance practitioners coordinate the plan as one team: your health pitstop crew.

Follow-up appointments are 60 minutes, allowing the team to review trends, symptoms, treatment response and next steps. Blood testing and functional medicine sit alongside the wider Formula Health service, including women’s health, nutrition, performance and advanced medical care. Formula Health services

Medical disclaimer: This article provides general information and does not replace individual medical advice. Reference ranges vary between laboratories and must be interpreted by an appropriately qualified clinician. Do not start, stop or change prescribed medication or supplementation without clinical advice. Persistent or severe fatigue requires appropriate medical assessment.

References

Truong J, Naveed K, Beriault D, et al. The origin of ferritin reference intervals: a systematic review. The Lancet Haematology. 2024;11:e530–e539.
Rodgers S, Woolley T, Smith J, et al. Updated adult ferritin reference intervals based on a large healthy UK sample. Annals of Clinical Biochemistry. 2024;61:365–371.
American Society of Hematology. Clinical practice guideline for the diagnosis of iron deficiency. 2026. See also the ASH diagnostic guidance summary.
Yokoi K, Konomi A. Iron deficiency without anaemia is a potential cause of fatigue. British Journal of Nutrition. 2017.
Houston BL, et al. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults. BMJ Open. 2018.
Sholzberg M, et al. Diagnosis and management of iron deficiency in females. CMAJ. 2025.
Nexo E, Parkner T. Vitamin B12-related biomarkers. Annals of Clinical Biochemistry. 2024.
High serum total vitamin B12 may mask biologically active B12 deficiency. Annals of Clinical Biochemistry. 2024.
Fedosov SN. Biomarkers and algorithms for the diagnosis of vitamin B12 deficiency. Frontiers in Molecular Biosciences. 2016.
Homocysteine, B vitamins and cardiovascular risk.
Subclinical hypothyroidism: when to treat. Cleveland Clinic Journal of Medicine. 2019.
The optimal healthy ranges of thyroid function defined by cardiovascular disease and mortality risk. The Lancet Diabetes & Endocrinology. 2023.
Jonklaas J, Bianco AC, Cappola AR, et al. Guidance for reverse triiodothyronine testing and free thyroxine and free triiodothyronine measurement: an American Thyroid Association clinical practice review. Thyroid. 2023.
Burmeister LA. Reverse T3 or perverse T3? Still puzzling after 40 years. Cleveland Clinic Journal of Medicine. 2018;85(6):450–455.
Proposal for fasting insulin and HOMA-IR reference intervals. Archives of Endocrinology and Metabolism.
Optimal cut-offs of HOMA-IR to identify dysglycaemia and type 2 diabetes. PLOS ONE. 2016.
Early insulin resistance in normoglycaemic low-risk individuals and subclinical atherosclerosis. Cardiovascular Diabetology. 2023.
Scientific Advisory Committee on Nutrition. Vitamin D and health report. UK Government.
Christie F, et al. Vitamin D in the UK: an urgent call to redefine the threshold for deficiency. Frontiers in Endocrinology. 2026.
Workinger JL, Doyle RP, Bortz J. Challenges in the diagnosis of magnesium status. Nutrients. 2018.
Costello RB, et al. Recommendation on an updated standardisation of serum magnesium reference ranges. European Journal of Nutrition. 2022.
Colaneri-Day S, Rosanoff A. Clinical guideline for detection and management of magnesium deficiency in ambulatory care. Nutrients. 2025.
Effects of sleep fragmentation and estradiol decline on cortisol in a human experimental model of menopause. Journal of Clinical Endocrinology & Metabolism. 2023.
NICE. Menopause: diagnosis and management, NG23.
British Menopause Society and Women’s Health Concern. Hormone blood tests in the menopause transition. 2026.

Gemma Fisher

03/Aug/2026

Most of us expect to feel tired now and again. Life is busy. Between work, family, travel and everything else that fills our calendars, it is hardly surprising that we sometimes run out of steam.

However, there is a distinct difference between feeling tired after a busy week and feeling exhausted all the time.

If you are waking up unrefreshed, relying on coffee to get through the day, or finding that your energy just is not what it used to be, it is worth asking why. Many people put it down to stress, getting older or simply having too much on their plate. Sometimes that is true: but often there is more to the story.

At Formula Health, our award-winning multidisciplinary medical practice does not see fatigue as something to simply “put up with”. We see it as your body’s way of telling you that something deserves a closer look. Through our advanced integrated medicine approach, we combine elite sports diagnostics with personalised clinical care to uncover the root causes of persistent exhaustion.

Why Fatigue Rarely Has a Single Cause

One of the reasons persistent fatigue can be frustrating is that it rarely has a single cause.

Sometimes it is a vitamin or iron deficiency. Sometimes it is an underactive thyroid. For many women, hormonal changes during perimenopause or menopause can have a profound impact on energy levels. Poor sleep, chronic stress, anxiety, low mood, recovering from a viral illness or underlying conditions such as diabetes can all play a part too.

Often, it is a combination of several factors rather than one obvious problem.

That is why a quick appointment or a standard, surface-level set of blood tests does not always provide the whole picture. Standard reference ranges in conventional medicine can leave patients feeling dismissed when their results fall within broad parameters, yet they still feel profoundly unwell.

Good Medicine Starts with Listening

One of the biggest frustrations we hear from patients is, “My blood tests were normal, but I still don’t feel right.”

Normal results do not always explain how someone feels.

Before arranging any investigations at our clinic, our specialists spend time getting to know you. When did your symptoms begin? Has anything changed recently? How are you sleeping? Are you under more stress than usual? Have your hormones changed? Is your energy affecting your work, exercise or family life?

These conversations matter because they help us decide what needs investigating: and just as importantly, what does not. Our approach prioritises thorough clinical consultation to align diagnostic testing with your lived experience. You can explore our comprehensive range of services on our services page.

Looking Beneath the Surface

If diagnostic investigations are appropriate, we recommend them based on your precise symptoms and medical history, rather than deploying a one-size-fits-all approach.

Depending on your individual circumstances, we may assess areas such as:

Iron levels and ferritin status
Comprehensive thyroid function panels
Specific vitamin and mineral deficiencies (including Vitamin D, B12 and folate)
Blood sugar regulation and metabolic markers
Hormonal profiles relevant to men and women

The goal is not to order more tests. It is to order the right tests. By utilising targeted diagnostics, we build a clearer, clinically actionable picture of your health.

Finding the Right Solution

Once we understand what is contributing to your fatigue, we formulate a treatment plan that is entirely tailored to your biology.

For some individuals, correcting an iron deficiency or optimising thyroid function is enough to make a significant difference. Others benefit from addressing hormone health, improving sleep architectures, managing chronic stress more effectively or making targeted lifestyle and nutritional adjustments. Sometimes, it is a combination of several small, strategic changes that yields the most substantial clinical impact.

There is no one-size-fits-all treatment because there is no one-size-fits-all patient. Our multidisciplinary team works collaboratively to ensure every aspect of your physiological wellbeing is supported under one roof.

Reclaiming Your Vitality

Many people live with fatigue for months: or even years: because they assume it is simply an inevitable part of getting older or leading a demanding life.

It isn’t always.

If you are constantly running on empty, your body may be trying to signal an imbalance. At Formula Health, we take the time to understand what is truly going on beneath the surface, so together we can find the cause: not just manage the symptoms.

Because good health is not simply about avoiding illness. It is about having the sustained energy to enjoy your life, optimise your performance, and maintain long-term vitality.

If persistent fatigue has become your normal, we would be delighted to help you find out why. Contact our team today to arrange a comprehensive consultation at our practice.

Gemma Fisher

03/Aug/2026

Magnesium is an essential cofactor in over 300 enzymatic reactions, yet modern dietary intake and clinical assessments frequently reveal widespread sub-optimal status. Because different magnesium salts exhibit distinct bioavailability, gastrointestinal tolerance, and tissue-specific targeting, selecting the appropriate compound is critical for clinical efficacy.

This guide outlines the pharmacological profiles, clinical evidence, and precise dosing protocols for the eight primary forms of supplemental magnesium, alongside advanced diagnostic considerations at Formula Health.

Quick-Navigation: Find Your Concern

Sleep, Anxiety, & Daily Supplementation: Magnesium Glycinate
Cognitive Function & Memory: Magnesium L-Threonate
Cardiovascular Support & Palpitations: Magnesium Taurate
Energy Production & Muscle Pain: Magnesium Malate
Acute Constipation & Bowel Motility: Magnesium Citrate
Forms to Avoid or Restrict: Magnesium Oxide, Magnesium Chloride, and Magnesium Sulfate

The 8 Types of Magnesium Compared

1. Magnesium Glycinate (Bisglycinate)

Primary Indication: Sleep architecture enhancement, anxiety modulation, and general daily repletion.
Mechanism & Pharmacokinetics: Bound to the amino acid glycine, this compound is absorbed intact via amino acid transport channels, bypassing competitive mineral absorption pathways. It demonstrates exceptional bioavailability and minimal gastrointestinal irritation. Glycine acts concurrently as an inhibitory neurotransmitter in the central nervous system, conferring synergistic calming properties.
Clinical Evidence: Supported by trials evaluating sleep latency improvements and neurological relaxation.
Dose: 200–400 mg of elemental magnesium daily, administered in the evening.

2. Magnesium L-Threonate

Primary Indication: Cognitive optimisation, memory enhancement, and mitigation of cognitive fatigue (“brain fog”).
Mechanism & Pharmacokinetics: Engineered at the Massachusetts Institute of Technology (MIT) specifically to elevate magnesium concentrations within the central nervous system. It uniquely crosses the blood-brain barrier to increase synaptic density and plasticity.
Clinical Evidence: Slutsky et al. (Neuron, 2010) demonstrated significant enhancements in learning and working memory via cerebrospinal fluid elevation. (See also Maier et al., 2020). Note that elemental yield per capsule is relatively low (~48 mg per 2,000 mg compound), frequently necessitating combination with secondary formulations.
Dose: 1,000–2,000 mg of total compound daily, divided into morning and evening doses.

3. Magnesium Taurate

Primary Indication: Cardiovascular support, blood pressure regulation, and management of ectopic heartbeats or palpitations.
Mechanism & Pharmacokinetics: Chelated with taurine, an amino acid highly concentrated in cardiac tissue. Taurine modulates intracellular calcium signaling, vascular tone, and myocardial contractility.
Clinical Evidence: Demonstrates cardioprotective efficacy through synergistic attenuation of sympathetic nervous system activity and vascular resistance.
Dose: 200–400 mg of elemental magnesium daily.

4. Magnesium Malate

Primary Indication: Cellular energy production, chronic fatigue, fibromyalgia, and musculoskeletal tenderness.
Mechanism & Pharmacokinetics: Bound to malic acid, a key intermediate in the Krebs (citric acid) cycle. Malate directly participates in adenosine triphosphate (ATP) synthesis within mitochondria.
Clinical Evidence: Abraham & Flechas (J Nutr Med, 1992) highlighted significant reductions in tenderness and pain scores in fibromyalgia cohorts receiving malate supplementation. Morning administration is preferred to support daytime metabolic output.
Dose: 200–400 mg of elemental magnesium daily, taken with breakfast.

5. Magnesium Citrate

Primary Indication: Acute constipation and rapid restoration of bowel motility.
Mechanism & Pharmacokinetics: Bound to citric acid, exhibiting moderate-to-high systemic absorption while exerting an osmotic effect by drawing water into the intestinal lumen.
Clinical Evidence: Well-established in gastroenterology for acute repletion and colonic clearance, though higher doses frequently induce loose stools.
Dose: 150–300 mg of elemental magnesium, adjusted according to bowel tolerance.

6. Magnesium Oxide

Primary Indication: Not recommended for systemic repletion.
Mechanism & Pharmacokinetics: Possesses an extremely low systemic bioavailability of approximately 4%. It functions predominantly as a robust osmotic laxative and gastric antacid.
Clinical Evidence: Due to poor intestinal uptake and high incidence of osmotic diarrhoea, it represents an inefficient modality for cellular magnesium repletion.

7. Magnesium Chloride

Primary Indication: Topical application via transdermal oils, lotions, and balms.
Mechanism & Pharmacokinetics: Applied directly to the integumentary system. While widely utilised in athletic recovery, clinical data confirming significant transdermal absorption into systemic circulation remain limited (Gröber et al., 2017).
Dose: Applied topically to target muscle groups as required.

8. Magnesium Sulfate

Primary Indication: Epsom salt baths for localised musculoskeletal relaxation.
Mechanism & Pharmacokinetics: Dissolved in warm bath water. Evidence supporting substantial percutaneous absorption of magnesium ions into the bloodstream remains inconclusive, though warm water immersion provides proven thermal and myofascial benefits.
Dose: 2 cups of Epsom salts dissolved in a warm bath for 20 minutes.

Recognising Magnesium Deficiency

Sub-optimal magnesium status manifests across multiple physiological systems. Clinical indicators of deficiency include:

Neuromuscular cramps and fasciculations
Insomnia and fragmented sleep architecture
Heightened anxiety and autonomic hyperarousal
Cardiac palpitations and arrhythmias
Chronic fatigue and diminished exercise recovery
Constipation and sluggish gastrointestinal transit
Cognitive impairment and executive dysfunction
Tension headaches and migraines

Diagnostic Limitations: Serum vs. RBC Magnesium

Standard clinical panels routinely utilise serum magnesium testing. However, serum levels represent less than 1% of total body magnesium, as serum homeostasis is tightly regulated via renal conservation and bone resorption. Consequently, an individual may present with a normal serum magnesium level while experiencing profound intracellular depletion.

Formula Health prioritises Red Blood Cell (RBC) magnesium analysis. RBC magnesium provides a superior clinical reflection of tissue loading over a 90-day erythrocyte lifespan, enabling precise identification of sub-clinical deficiencies.

Etiology of Deficiency in Modern Populations

Systemic depletion arises from a confluence of environmental, dietary, and pharmacological factors:

Agrarian Depletion: Intensive monoculture farming and industrial soil exhaustion have significantly reduced magnesium concentrations in staple crops.
Water Treatment: Modern municipal water purification frequently strips natural mineral content.
Dietary Processing: Refining whole grains removes the germ and bran fractions where magnesium is predominantly concentrated.
Chronic Stress: Elevated cortisol and catecholamines accelerate urinary excretion of magnesium.
Iatrogenic Factors: Long-term administration of proton pump inhibitors (PPIs) and loop or thiazide diuretics impairs intestinal absorption and increases renal clearance.

Dietary Sources

While targeted supplementation corrects established deficits, foundational intake should be supported through whole foods rich in magnesium:

Pumpkin seeds: ~262 mg per 30g serving
Chia seeds: ~111 mg per 30g serving
Almonds: ~80 mg per 30g serving
Spinach (cooked): ~157 mg per cup
Dark chocolate (70–85% cacao): ~64 mg per 30g serving
Avocado: ~58 mg per medium fruit

Pharmacological Interactions & Safety Considerations

Supplemental magnesium requires careful management in patients taking specific medications:

Drug Interactions: Separate oral magnesium administration by at least two hours from bisphosphonates, tetracycline antibiotics, and levothyroxine to prevent chelation and impaired drug absorption.
Upper Limit Considerations: The European Food Safety Authority (EFSA) and regulatory bodies establish a tolerable upper intake level of 250 mg/day for supplemental magnesium to avoid osmotic laxative side effects, though higher clinical doses are utilised under medical supervision. Contraindications apply to individuals with advanced renal impairment or severe bradycardia.

Precision Healthcare at Formula Health

Correcting nutritional deficiencies requires an evidence-based, individualised strategy rather than generalised supplementation. At Formula Health, our award-winning multidisciplinary medical practice integrates advanced diagnostics: including comprehensive micronutrient profiling and RBC magnesium testing: with expert clinical oversight.

Our practitioners combine elite sports medicine technology with functional medicine to design bespoke supplementation and lifestyle protocols tailored to your exact biological requirements. Explore our tests and analysis services to begin your journey toward optimal human performance.

Osteogem01

05/Jun/2024

Our ability to succeed at most things in life can often come down to one main factor…“Have I got the energy to do this?!” Whatever form that success may look like, whether that’s the energy to take on more responsibility in the workplace, the energy to go out for that run you’ve been meaning to, the energy to finally get that renovation project finished or the energy to spend some quality time playing with your family in the park.

This article explores various different energy systems of the body and breifly discusses how to optimise them.

If you have any questions or concerns about your energy levels or would like to have an exploratory discussion with one of our practitioners, please don’t hesitate to get in touch.

#StayEnergised #HighEnergy #BoostYourEnergy #EnergyTips #NaturalEnergy #EnergyLevels #FeelTheEnergy #EnergyHack #EnergyJourney #EnergiseYourDay #biohacking #healthoptimisation #integratedmedicine #functionalmedicine #nutrition

Read more about the benefits of Nutrigenetic analysis and the wide range of health insights you can gain by visiting the DNA service page on our website where you can download a free information brochure and learn about the 1-to-1 Nutritional Therapist support packages that we offer alongside our test kits.

Keep up with the latest news, events and offers from Formula Health by joining us on social media.

Don’t forget to keep in touch, we love hearing from you and seeing pictures of our clients progress!

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Gemma Fisher

29/Mar/2023

Long Covid results in symptoms such as chronic fatigue, brain fog, muscle aches, anxiety, disrupted sleep and can prevent people from going about their daily lives and the ability to live life to the full.

Here at Formula Health, we offer a 6 week multidisciplinary programme to support people with Long Covid. Treatments will include Acupuncture, Kinesiology with Reiki and a one-to-one Qigong session to provide a gentle supportive exercise to do alongside.

In this way, we aim to bring people back to good health.

The British Acupuncture Council has found that recent studies show acupuncture to be an effective treatment for the symptoms of Long Covid. Acupuncture has an anti-inflammatory action and modulates the immune system.

Kinesiology uses muscle testing to find imbalances in the body and the most effective way of bringing balance and well-being back, whether it be through emotional and stress release techniques, identifying the best nutritional support, structural realignment, or energy work. Reiki is a healing modality which channels energy into the body so vitality is restored. Reiki is integrated within the Kinesiology treatment; it is a therapy that aims to heal the body as a whole.

The kinesiology treatment will include testing whether Medicinal Mushrooms are appropriate to take for aiding in recovery. There is increasing research into the benefits and efficiency of medicinal mushrooms supporting the recovery from Long Covid.

This package includes:

3x Acupuncture appointments

3x Kinesiology & Reiki combined appointments

1x 1-to-1 intro to Qigong session

70x capsules Medicinal Mushrooms known to support those with Long Covid

If you are experiencing symptoms of Long Covid and would like to find out more about the programme contact us at info@formulahealth.co.uk or call 0118 4181825.

References

[1] Long Covid – British Acupuncture Council