What supplements do vegans need?

A dairy cow does not eat vitamin B12. She builds it in her rumen out of cobalt, and the cobalt goes into her feed at a specified rate. The requirement is set at 0.2 mg per kilo of dietary dry matter, only 3-15% of it ever becomes B12, and how much she ends up making depends on the make-up of the ration she is given.

A vegan taking a B12 tablet and a dairy operation dosing cobalt into feed are working on the same problem from opposite ends. Industrial food does not reliably supply this vitamin unaided, whatever is on the plate. Which reframes the question worth asking: what does a plant-exclusive diet actually require, once you set aside the idea that supplementing is an admission of failure? One thing, without exception. The rest is diet quality.

Why is B12 the only non-negotiable?

Because it is the one nutrient no unfortified plant food supplies. B12 is made by bacteria and archaea rather than by plants or animals, and animals carry it only because they eat it, host the microbes that make it, or get it added to their feed. The Academy of Nutrition and Dietetics states it plainly: a reliable source of B12 is required, from fortified food or a supplement, and an appropriately planned vegan diet is nutritionally adequate once that source is in place. Their 2016 position covers all stages of the life cycle; the 2025 update covers nonpregnant, nonlactating adults.

Ask how common deficiency is and the answer turns on the tablet, not the diet. Between 3% and 43% of older adults are deficient regardless of what they eat, because the stomach acid needed to absorb B12 from food declines with age. Among plant-exclusive eaters the split runs sharper: a 2019 study of 151 Czech vegans found lab signs of deficiency in 52.9% of those taking no supplement, against 5.6% of those supplementing regularly. A 2014 review of the wider literature puts the range broader still, from 0% to 86.5%, depending on the population and its supplement habits.

The adult requirement is 2.4 mcg a day, covered by fortified nutritional yeast, fortified cereals or a direct supplement. Tablet doses often run far higher, at 500 or 1,000 mcg, because the body absorbs only a small fraction of what is available at once. That is a quirk of B12 absorption rather than evidence anyone needs enormous amounts.

Do you need a vitamin D supplement?

Not as a diet matter. Vitamin D deficiency tracks sun exposure, skin tone, age and latitude rather than what you eat. The adult requirement is 15 mcg (600 IU) up to age 70, rising to 20 mcg after. Plant sources exist and work: most fortified soy, almond and oat milks carry close to the same 120 IU per cup that dairy milk does, and some mushrooms are UV-treated to raise their D content. Anyone with limited sun needs to watch this one in winter, whatever their diet.

How common are these deficiencies in everyone else?

Set the diet question aside and look at the general population. A 2023 pooled analysis of 7.9 million people across 81 countries found 47.9% with vitamin D below 50 nmol/L, and 15.7% below 30 nmol/L, the floor every major clinical guideline agrees should be avoided at any age. For B12, analyses pooling data from Europe, North America and Asia put general-population deficiency between 5% and 20%, depending on age, diet and income.

Now the other number. Gallup puts vegans at 1% of American adults and vegetarians at 4%, figures that have barely moved in two decades.

Put those side by side and the arithmetic is hard to avoid. If close to half the world is short on vitamin D and roughly one adult in a hundred is vegan, then almost every vitamin D deficient person alive eats animal products. The same holds for B12 at 5-20%. These are population-wide deficiencies that happen to get argued about as though diet type were the variable under test.

One honest limit on that comparison: the deficiency figures are global and the vegan figure is American. Reliable worldwide data on how many people are vegan does not exist. The numbers in circulation trace mostly to market-research surveys rather than population studies, and they disagree with each other by a factor of three. The US figure is used here because its methodology is public and its trend line is long.

Do you need an iodine supplement?

Often, and this is the one people forget. Iodine builds thyroid hormone, and the risk here is real and diet-specific: the NIH lists people who eat little or no dairy, seafood and eggs as a genuine at-risk group, alongside pregnant women and anyone avoiding iodised salt. The US adult requirement is 150 mcg a day; the UK recommendation sits slightly lower at 140 mcg. Iodised salt is the simplest cover, carrying about 45 mcg per gram, so half a teaspoon across a day of cooking clears it. Note that sea salt, pink Himalayan and most finishing salts are not iodised. A supplement, if needed, should specify potassium iodide or iodate rather than kelp, where content swings too unpredictably to dose safely.

How do you get omega-3 without fish oil?

Through algal oil. Plant foods supply ALA, in flaxseed, walnuts, canola and soybean oil, which is the essential form and the one plant eaters do get enough of. The adult requirement is 1.6 g a day for men and 1.1 g for women. The catch is that the body converts only very small amounts of ALA into the EPA and DHA that heart and brain tissue use. Algal oil supplies EPA and DHA directly, from the algae fish get it from in the first place, and it sits on the shelf beside fish oil and cod liver oil as a recognised supplement form.

What about iron, zinc and calcium?

These depend on what is on the plate rather than being an automatic gap. Plant iron and zinc absorb less efficiently than their animal-food counterparts, but that is a pairing-and-planning problem with a food answer. Vitamin C alongside iron-rich meals helps, and soaking or sprouting beans releases zinc that phytate was holding. Better assessed with a food record or a blood test than by reflexively adding a pill.

What should you do?

If you eat plant-exclusively: get a B12 supplement into a daily or weekly habit. It is the one item here with no food-only workaround, and the evidence shows supplementation, rather than diet duration or general care, is what closes the gap. Check a fortified plant milk's label for iodine and vitamin D before assuming they are covered, because plenty of brands fortify with one and not the other. Consider algal oil if flax or walnuts are not already regular. Everything else is worth checking with bloodwork if you have a specific concern.

If you do not: the B12 numbers above are an ageing problem rather than a vegan one. Up to 43% of older adults are affected regardless of diet, largely because stomach acid production drops with age. Past 50, a B12 check is worth asking for the same way you would ask about any other routine bloodwork. Iodine is not automatically solved by eating dairy or fish either; cutting back on both without switching to iodised salt carries the same risk this article describes.

That is the honest shortlist. B12 is the one nothing on a plant-exclusive plate supplies on its own. Iodine and omega-3 need specific attention because most food sources are animal-based by default. Vitamin D is everyone's seasonal problem. Everything past that is a question of what is being eaten.