What do vegans actually need to test for, and what's safe to just take?

Which vegan supplements are needed, and who should see a clinician first?

A planned vegan diet covers most nutrients, but the NHS names vitamin B12, vitamin D, iodine, calcium, iron, omega-3 fats and selenium as the ones to plan for. They fall into three groups: take (B12, vitamin D, and usually iodine), test first (iron) and food first (calcium, zinc and omega-3).

See a GP, family doctor or primary-care clinician before supplementing if any of these apply:

• You have symptoms such as unusual tiredness, breathlessness, pins and needles, numbness or problems with balance. Starting B12 before a test can make the result look normal without fully treating a deficiency, according to NICE.
• You're pregnant, trying to conceive or breastfeeding. Babies breastfed by vegan mothers with low B12 can develop serious deficiency early in life, warns the NIH Office of Dietary Supplements.
• You're choosing supplements for a child. Doses and safe limits differ by age; the NHS sets lower vitamin D limits for children, for example.
• You take medicines that interact, or have a thyroid condition: metformin and stomach-acid medicines such as omeprazole can lower B12; iron taken within four hours of levothyroxine reduces its absorption, according to the NIH Office of Dietary Supplements; and high-dose iodine adds to antithyroid drugs.

Do vegans need B12? Yes, every one

Natural B12 sources are limited to animal foods, so vegans have a higher risk of deficiency, and fortified foods or supplements substantially reduce it, according to the NIH Office of Dietary Supplements. Deficiency can cause anaemia and nerve damage; the NHS lists a vegan diet without B12 supplements as a cause.

The Vegan Society gives three options, and the British Dietetic Association agrees:

• fortified foods two or three times a day, adding up to at least 3 micrograms of B12 a day; or
• one daily supplement of at least 10 micrograms; or
• one weekly supplement of at least 2,000 micrograms.

The official adult requirement is 2.4 micrograms a day in the US and Canada. According to the NHS, fortified foods include some breakfast cereals, unsweetened soya drinks, yeast extract and nutritional yeast flakes; check the label, because not all brands add B12.

Testing B12: when it helps, and its limits

If you have symptoms, NICE NG239 counts a vegan diet without regular B12 supplements as a risk factor, and a symptom plus a risk factor should mean a test. The first test is total B12 or "active B12" (holotranscobalamin):

• Total B12 below 180 ng/L (133 pmol/L), or active B12 below 25 pmol/L: deficiency confirmed.
• Total B12 of 180–350 ng/L, or active B12 of 25–70 pmol/L: indeterminate. NICE suggests a further test, methylmalonic acid (MMA), if you have symptoms.

US labs report pg/mL, the same number as ng/L; the NIH Office of Dietary Supplements notes experts suggest checking MMA when B12 is 150–399 pg/mL. The Vegan Society considers blood B12 unreliable for vegans and names MMA as the most specific test. Tell whoever tests you if you already take B12.

Vitamin D and iodine: take at official doses, with a few cautions

Vitamin D

Deficiency is more common in vegans, according to the NIH Office of Dietary Supplements. Our guide to how much vitamin D to take in winter compares the advice in detail.

• UK: the NHS says everyone should consider 10 micrograms (400 IU) a day in autumn and winter, and all year if you're rarely outdoors or cover most of your skin. Don't take more than 100 micrograms (4,000 IU) a day.
• US: the recommended intake is 600 IU (15 micrograms) a day up to age 70 and 800 IU (20 micrograms) over 70, from food and supplements combined.
• Canada: the same 600–800 IU recommendation, and Canada's Food Guide advises adults 51 and over to take a 400 IU (10 microgram) supplement every day.

Check the source: vitamin D2 is made from yeast, most D3 comes from sheep's wool, and a lichen-based D3 is available. Most evidence suggests D3 raises blood levels more than D2.

Iodine

Iodine mostly comes from dairy, fish and eggs. Adults need 140 micrograms a day in UK guidance and 150 micrograms in North America.

• UK: iodised salt is not widely available. Choose iodine-fortified plant drinks (not all are) or discuss a supplement; the NHS says 0.5 mg (500 micrograms) or less a day is unlikely to cause harm.
• Canada: table salt must contain added iodide.
• US: iodising salt is voluntary, so check the label.

Don't rely on seaweed: its iodine ranges from 16 to 2,984 micrograms per gram, and the British Dietetic Association advises against seaweed or kelp supplements as a source. Too much iodine can disturb the thyroid, and people with autoimmune thyroid disease can react to amounts safe for others, so if you have a thyroid condition, ask your clinician before taking iodine. There's no useful individual test: spot urine samples describe populations, not one person.

Iron: why vegans should test before taking it

Vegans need more iron than meat eaters: the requirement is 1.8 times higher on a vegetarian diet because plant iron is absorbed less well. But test, don't guess: extra iron isn't harmless, and low iron can come from blood loss as well as diet. Eat pulses, wholemeal bread, fortified cereals and dark green vegetables, and if you have symptoms ask for ferritin and a full blood count. Our guides explain why to test before taking iron and why ferritin, not serum iron, is the number to ask for.

Calcium, zinc and omega-3: food first

Calcium. Vegans have a higher risk of low intake, says the NIH Office of Dietary Supplements. UK adults need about 700 mg a day, according to the British Dietetic Association; US and Canadian adults aged 19–50 need 1,000 mg. Good sources are calcium-fortified plant drinks, calcium-set tofu, tahini, pulses and green leafy vegetables. If you do take a supplement, doses of 500 mg or less absorb best.

Zinc. Vegans tend to have lower zinc intakes and blood levels because phytates in grains and pulses reduce absorption, notes the NIH Office of Dietary Supplements. Adults need 11 mg (men) or 8 mg (women) a day in Canadian and US guidance.

Omega-3. The only omega-3 with an official intake is ALA: 1.6 g a day for men and 1.1 g for women. There's no set requirement for the long-chain fats EPA and DHA, and several large heart trials of omega-3 supplements had largely null results, according to the NIH Office of Dietary Supplements. Linseed, chia, hemp seeds and walnuts provide ALA. Algal oil, usually 100–300 mg of DHA, is a vegan option; pregnant vegans should ask whether they need it.

Free testing and official advice: US, Canada and UK

United States

When a primary-care clinician orders B12, ferritin or a full blood count because of symptoms, it's billed to insurance as a diagnostic test, with your usual cost-sharing. Without insurance, community health centers charge according to income.

Canada

In Ontario, OHIP covers medically necessary lab tests ordered by a doctor, nurse practitioner or midwife, but a vitamin D test is covered only for specific conditions. In other provinces, ask your family doctor or a walk-in clinic for a requisition. Pregnant people are advised to take a multivitamin with 0.4 mg folic acid and 16 to 20 mg of iron.

United Kingdom

A GP can order B12, ferritin and a full blood count free on the NHS when you have symptoms; under NICE's symptom-plus-risk-factor rule, a vegan diet without regular B12 supplements counts as a risk factor. Vitamin D tests usually need a medical reason. See free care routes in the US, Canada and UK if you don't have a regular GP.

Compare: what vegans should test, take or eat

What to do next

1. Sort out B12 today: fortified foods twice or three times a day, or a supplement at the Vegan Society's amounts.
2. Add vitamin D at your country's official dose, from a vegan source.
3. Cover iodine with fortified drinks, iodised salt where it's sold, or a supplement, after checking with a clinician if you have a thyroid condition.
4. Don't start iron without a test. Ask for ferritin and a full blood count if you're tired or breathless.
5. Get calcium, zinc and omega-3 from food, and review supplements with a clinician if you're pregnant, choosing for a child, or take regular medicines.

Common questions

Related guides

• Which vitamin D test do you actually need, and when is it free?
• Always tired? The five blood tests worth asking for
• Do I need a multivitamin? What the evidence says

Sources

1. NHS. The vegan diet — nutrients to plan for and food sources.
2. The Vegan Society. What every vegan should know about vitamin B12. Accessed 20 October 2026.
3. British Dietetic Association. Vegetarian, vegan and plant-based diet: food fact sheet.
4. NIH Office of Dietary Supplements. Vitamin B12 — fact sheet for health professionals.
5. NICE. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239), 2024.
6. NHS. Vitamin B12 or folate deficiency anaemia.
7. NHS. Vitamin D — who should take a supplement and how much.
8. NIH Office of Dietary Supplements. Vitamin D — fact sheet for health professionals.
9. Health Canada. Canada's Food Guide — advice on vitamin and mineral supplementation.
10. Health Canada. Dietary Reference Intakes — reference values for vitamins.
11. Health Canada. Dietary Reference Intakes — reference values for elements (minerals).
12. NHS. Iodine.
13. British Dietetic Association. Iodine: food fact sheet.
14. NIH Office of Dietary Supplements. Iodine — fact sheet for health professionals.
15. Canadian Food Inspection Agency. Labelling requirements for salt — iodide in table salt.
16. NIH Office of Dietary Supplements. Iron — fact sheet for health professionals.
17. NIH Office of Dietary Supplements. Calcium — fact sheet for health professionals.
18. NIH Office of Dietary Supplements. Omega-3 fatty acids — fact sheet for health professionals.
19. NIH Office of Dietary Supplements. Zinc — fact sheet for health professionals.
20. Health Canada. Canada's Food Guide — healthy eating when pregnant and breastfeeding. Updated April 2026.
21. Government of Ontario. What OHIP covers — laboratory tests. Accessed 20 October 2026.
22. HealthCare.gov. Community health centers — low-cost care based on income.

General information, not medical advice — see our medical disclaimer. Written to the WhereToStart editorial policy. Next scheduled review: 20 April 2027.