Vitamins, minerals and when supplementation is medical

There is a clear distinction between supplementation as a treatment for documented deficiency and supplementation as a consumer product, and the first is where the value is.

Iron deficiency

The most common nutritional deficiency worldwide.

Symptoms: fatigue, breathlessness on exertion, pallor, hair loss, brittle nails, restless legs, poor concentration and reduced exercise capacity.

Ferritin is the main measure of stores, and deficiency can be present with a normal haemoglobin — which is why testing ferritin matters and why "your blood count is normal" is not the whole answer.

Ferritin rises with inflammation, which can mask deficiency.

The critical clinical point: iron deficiency in an adult, particularly a man or a postmenopausal woman, requires investigation of the cause rather than only replacement, since gastrointestinal blood loss including from cancer is a possibility.

Treatment is oral iron, which is cheap, and where alternate-day dosing has evidence for better absorption and fewer side effects than daily dosing.

Taking it with vitamin C and away from tea, coffee, calcium and antacids improves absorption.

Vitamin B12

Consequential when missed.

Deficiency causes anaemia and neurological effects — numbness, tingling, unsteadiness, cognitive change — which can become irreversible if untreated.

Causes: pernicious anaemia, which is autoimmune; vegan and vegetarian diets; metformin use; proton pump inhibitor use; gastric surgery; and malabsorption.

Treatment depends on cause: injections for absorption problems, and oral supplementation for dietary deficiency.

Importantly, folate should not be given alone where B12 deficiency is possible, since it can correct the anaemia while neurological damage progresses.

Vitamin D

Where population supplementation is recommended.

Deficiency is common at higher latitudes, in people with darker skin, in those who cover up or stay indoors, in older adults and with obesity.

Severe deficiency causes rickets and osteomalacia.

Guidance in many countries recommends a daily supplement for the whole population during winter and year-round for at-risk groups.

Routine testing is not recommended in most guidance, since it does not change the advice.

High-dose products bought online have caused documented toxicity, which is why following stated doses matters.

Folate

Where timing is everything.

Supplementation before conception and in early pregnancy prevents neural tube defects, with strong evidence, and must be taken before the neural tube closes — which is before many pregnancies are recognised.

Which is why it is recommended for anyone who could become pregnant rather than only those actively trying.

Higher doses are recommended in specific circumstances including previous affected pregnancy, diabetes, obesity and certain medications.

Other deficiencies worth knowing

Less common and real.

Calcium, particularly with low dairy intake and in older adults.

Iodine, which matters in pregnancy for fetal brain development and where intake in some populations is marginal.

Zinc, in malabsorption and certain diets.

Thiamine, in alcohol dependence, where deficiency causes Wernicke's encephalopathy and where treatment is urgent.

Magnesium, in certain medication use and gastrointestinal disease.

And multiple deficiencies after bariatric surgery, where lifelong supplementation and monitoring are required.

Who should actually be tested

Targeted rather than broad.

People with symptoms consistent with a specific deficiency.

People with malabsorption conditions — coeliac disease, inflammatory bowel disease, previous gastrointestinal surgery.

People on medications affecting absorption.

People with restricted diets.

Pregnancy.

Older adults with poor intake.

And people with unexplained fatigue, where a targeted panel including full blood count, ferritin, B12, folate, thyroid function and coeliac serology is more useful than a broad screen.

The risks of over-supplementation

Which are real.

Iron overload, and iron overdose which is a serious poisoning particularly in children.

Vitamin D toxicity causing hypercalcaemia.

Vitamin A in high doses, teratogenic in pregnancy.

Vitamin B6 in high doses, causing peripheral neuropathy.

Interactions: high-dose vitamin E and fish oils with anticoagulants; calcium and iron with several medications; and biotin interfering with laboratory assays.

And the general principle that correcting deficiency helps while adding more to someone replete does not.

What to do

The practical sequence.

If you have symptoms, get tested for the specific things suggested rather than taking supplements speculatively.

If a deficiency is found, ask why, since the cause frequently matters more than the correction.

Take the treatment as prescribed and for the stated duration, since courses are frequently stopped early.

Have it rechecked to confirm correction.

And tell any clinician everything you take, since supplements interact and interfere.

General information only, not medical advice. Consult a qualified clinician about testing and treatment for deficiency, and do not take high-dose supplements without advice.