Vegan Blood Test UK: The Nutrients You Actually Need to Track — and How Often

Why vegans need blood testing

Plant-based diets exclude the richest dietary sources of several nutrients: B12 (found almost exclusively in animal products), haem iron (2–3× more bioavailable than plant iron), EPA and DHA omega-3 (concentrated in oily fish), and iodine (mainly from dairy and seafood in the UK diet).

Deficiencies in these nutrients don’t announce themselves early. B12 stores can last 2–5 years after going vegan, meaning you can feel fine for years while neurological damage accumulates. Iron depletion progresses through three stages before you become anaemic. Vitamin D deficiency often presents as vague fatigue that gets blamed on the British weather.

The British Dietetic Association confirms that a well-planned vegan diet is suitable for every stage of life — but “well-planned” requires knowing where your levels actually sit. A blood test replaces guesswork with data.

The 10 markers every vegan should track

1. Vitamin B12 — the non-negotiable

B12 is involved in DNA synthesis, red blood cell formation and myelin sheath maintenance. There are no reliable plant sources of active B12. Nori, spirulina and nutritional yeast contain analogues that can actually interfere with true B12 absorption.

The NHS reference range for serum B12 is 200–900 ng/L. But functional deficiency can occur well within the “normal” range. Many clinicians consider levels below 300 ng/L as a grey zone warranting further investigation with active B12 (holotranscobalamin) or methylmalonic acid (MMA).

EPIC-Oxford found that 52% of vegans had serum B12 below 200 ng/L, compared to 7% of vegetarians and virtually none of the meat eaters. This doesn’t mean a vegan diet fails — it means supplementation and monitoring aren’t optional.

Supplementation: The Vegan Society recommends either 10 µg daily, 2,000 µg weekly, or fortified foods providing at least 3 µg/day from two servings. Cyanocobalamin is the most studied and cost-effective form.

Read more: Vitamin B12 Blood Test UK — full guide

2. Iron (ferritin & iron studies)

Plants contain only non-haem iron, which is absorbed at roughly 2–20% efficiency depending on the meal — compared to 15–35% for haem iron from meat. Phytates in wholegrains, legumes and nuts further inhibit absorption. The NICE CKS guidance on iron deficiency notes that premenopausal women on restricted diets are at particular risk.

Ferritin is the gold-standard marker for iron stores. The NHS lower limit is typically 15–30 µg/L, but symptoms of depletion — fatigue, hair thinning, restless legs, poor exercise tolerance — can appear at levels below 50 µg/L. Iron studies (serum iron, TIBC, transferrin saturation) help distinguish true deficiency from inflammation-driven low iron.

Practical tip: Pair iron-rich foods (lentils, tofu, dark leafy greens, pumpkin seeds) with vitamin C to boost absorption. Avoid tea and coffee within an hour of iron-rich meals — tannins reduce non-haem iron absorption by up to 60%.

Read more: Iron Deficiency Blood Test UK — full guide

3. Vitamin D

Vitamin D deficiency is common across the entire UK population — SACN’s 2016 report found that roughly 1 in 5 adults have serum 25(OH)D below 25 nmol/L. For vegans, the risk is amplified: most dietary vitamin D3 comes from oily fish, egg yolks and fortified dairy. Vitamin D2 (ergocalciferol, from mushrooms exposed to UV) is less effective at raising blood levels than D3.

The NHS considers levels below 25 nmol/L as deficient. Many functional medicine practitioners target 75–100 nmol/L for optimal bone health, immune function and mood regulation.

Supplementation: The UK government recommends 10 µg (400 IU) daily for all adults during autumn and winter. Vegans should use lichen-derived D3 (vegan) rather than lanolin-derived D3 or D2. Those with levels below 50 nmol/L may need higher loading doses — your GP can advise.

Read more: Vitamin D Deficiency UK — full guide

4. Omega-3 index (EPA & DHA)

The omega-3 index measures EPA and DHA as a percentage of red blood cell membrane fatty acids. The target is 8–12%. Most UK adults sit at 4–5%, and vegans — without any dietary source of preformed EPA or DHA — often fall below 4%.

Plants provide ALA (alpha-linolenic acid) from flaxseed, chia, hemp and walnuts. But the human body converts ALA to EPA at roughly 5–10%, and to DHA at less than 1%. For practical purposes, vegans cannot reach an optimal omega-3 index through ALA alone.

Supplementation: Algal oil (derived from marine microalgae) provides preformed DHA and EPA without fish. A typical dose of 250–500 mg combined EPA+DHA daily is consistent with NICE CG181 cardiovascular prevention guidance.

Read more: Omega-3 Blood Test UK — full guide

5. Zinc

Zinc is essential for immune function, wound healing, testosterone production and taste perception. The richest dietary sources are red meat, shellfish and dairy. Plant sources (legumes, seeds, wholegrains) contain zinc, but phytates bind to it and reduce absorption by up to 50%.

Serum zinc is the standard blood test but it’s imperfect — levels can appear normal even with tissue depletion. Low zinc often presents as frequent infections, slow wound healing, poor appetite, or unexplained hair loss.

Practical tip: Soaking, sprouting and fermenting legumes and grains breaks down phytates and increases zinc bioavailability. Leavened bread (sourdough) provides more absorbable zinc than unleavened flatbreads.

6. Iodine (via thyroid function)

Iodine is required for thyroid hormone synthesis. In the UK, dairy and fish are the primary dietary sources — both absent from a vegan diet. A 2011 study in the British Journal of Nutrition found that UK vegan women had a median urinary iodine concentration of 56.7 µg/L — well below the WHO threshold of 100 µg/L for adequacy.

Routine blood tests don’t measure iodine directly. Instead, thyroid function (TSH, free T4, free T3) acts as a proxy. A rising TSH with normal T4 (“subclinical hypothyroidism”) in a vegan with no other risk factors should raise suspicion for iodine insufficiency.

Supplementation: The BDA recommends 150 µg/day for adults. Kelp supplements are unreliable — iodine content varies wildly between batches. A standardised potassium iodide supplement is more predictable.

Read more: Thyroid Blood Test UK — full guide

7. Folate

Vegans tend to have higher folate intake than the general population — dark leafy greens, legumes and fortified cereals are all rich sources. This is usually good news. But high folate can mask B12 deficiency by preventing the megaloblastic anaemia that would otherwise trigger diagnosis, while neurological damage from B12 depletion continues silently.

This is why NICE recommends testing B12 and folate together — never folate in isolation. If your folate is high and your B12 is low-normal, that’s a warning sign, not a clean bill of health.

8. Calcium & bone health

EPIC-Oxford reported that vegans who consumed less than 525 mg of calcium per day had a 30% higher fracture risk than meat eaters. Above that threshold, the difference disappeared. The UK RNI for calcium is 700 mg/day.

Blood calcium is tightly regulated by parathyroid hormone and rarely reflects dietary intake — your body strips calcium from bone to maintain blood levels. A bone profile (calcium, phosphate, ALP) combined with vitamin D gives a better picture of bone health than serum calcium alone.

Best vegan calcium sources: Fortified plant milks (check the label — not all are fortified), tofu set with calcium sulphate (350 mg per 100 g), kale, pak choi, sesame seeds, and fortified orange juice. Note: spinach is calcium-rich on paper but oxalates reduce absorption to roughly 5%.

9. Selenium

UK soil is naturally low in selenium compared to the Americas. Since the UK stopped importing North American wheat in the 1980s, population selenium intake has fallen. The British Nutrition Foundation notes that mean UK selenium intake is below the reference nutrient intake of 75 µg/day for men and 60 µg/day for women.

For vegans, the richest source is Brazil nuts — but selenium content varies up to 100-fold depending on soil. Two Brazil nuts per day is the common advice, but blood testing is the only way to confirm whether that’s actually working.

Selenium supports thyroid function (it’s required for the deiodinase enzymes that convert T4 to active T3), immune defence and antioxidant pathways. Low selenium combined with low iodine creates a compound thyroid risk that’s particularly relevant for vegans.

10. Full blood count

A full blood count (FBC) is the safety net that catches anaemia regardless of its nutritional cause. It measures haemoglobin, red cell count, MCV (mean cell volume), MCH, white cells and platelets.

For vegans, the key patterns to watch are:

• • Low haemoglobin + low MCV (microcytic) — suggests iron deficiency anaemia
• • Low haemoglobin + high MCV (macrocytic) — suggests B12 or folate deficiency anaemia
• • Normal haemoglobin but low ferritin— iron depletion without anaemia (stage 1–2 deficiency)

An FBC alone won’t tell you why you’re anaemic, but it tells you that something needs investigating.

Read more: Full Blood Count Explained — full guide | Anaemia Blood Test UK — full guide

How often should vegans get tested?

Read more: How Often Should You Get a Blood Test?

NHS vs private blood tests for vegans

The NHS is excellent at investigating symptoms. Where it falls short for vegans is proactive screening — most GPs won’t run omega-3, zinc or selenium tests on an asymptomatic patient, even if the dietary pattern makes deficiency likely.

Which Helvy panel is right for you?

Frequently asked questions