B12 is non-negotiable, but what about D3, DHA, iodine, and zinc? A no-nonsense guide.
9 min read
A well-planned vegan diet provides nearly everything your body needs. But "nearly" is doing real work in that sentence. There are a handful of nutrients that are genuinely difficult — or impossible — to get from plants alone. Knowing which supplements to take, and which you can skip, separates a thriving vegan from one who slowly develops deficiencies.
Vitamin B12 is produced by bacteria, not by animals or plants. Animals accumulate it from soil bacteria and supplemented feed; plants don't accumulate it at all. No amount of unwashed organic vegetables or fermented foods will reliably provide adequate B12 on a vegan diet. Nutritional yeast and some fortified foods can contribute, but supplementation is the only guarantee.
B12 deficiency is serious: it causes irreversible nerve damage, megaloblastic anemia, cognitive impairment, and elevated homocysteine (a cardiovascular risk factor). Deficiency can take years to manifest because the liver stores 3-5 years' worth, which is why new vegans feel fine initially even without supplementing.
Recommended dose: 50-100µg cyanocobalamin daily, or 2,000-2,500µg once per week. The daily low dose is preferred because B12 absorption is saturable — your body can only absorb about 1.5µg per meal via intrinsic factor, plus about 1% of the remaining dose via passive diffusion. A 50µg supplement yields approximately 2µg absorbed, which comfortably exceeds the 2.4µg RDA.
For a comprehensive deep dive, read our dedicated Vitamin B12: The One Non-Negotiable article.
⚠️ Don't rely on spirulina for B12
Vitamin D is synthesized by your skin when exposed to UVB radiation. If you live above 37°N latitude (most of Europe, Canada, and the northern US), your skin produces virtually no vitamin D from October through March. Even in sunny climates, modern indoor lifestyles and sunscreen use limit production.
Vitamin D deficiency is endemic in the general population — not just vegans — but vegans have fewer dietary sources since D3 is found primarily in fatty fish, egg yolks, and fortified dairy. Vitamin D2 (ergocalciferol) is vegan and available from UV-exposed mushrooms, but research suggests D3 (cholecalciferol) is more effective at raising and maintaining blood levels. Vegan D3 sourced from lichen is now widely available.
Recommended dose: 1,000-2,000 IU (25-50µg) daily of vegan D3 from lichen. Get your 25(OH)D blood level tested annually — aim for 75-125 nmol/L (30-50 ng/mL).
Your body can convert the short-chain omega-3 ALA (found in flaxseed, chia, hemp, and walnuts) into the long-chain forms EPA and DHA. But this conversion is inefficient — typically only 5-10% for EPA and 2-5% for DHA. DHA is critical for brain function, retinal health, and reducing systemic inflammation.
Fish get their DHA from algae. You can skip the fish and go directly to the source. Algal oil supplements provide preformed DHA and EPA in a bioavailable form without the mercury, PCBs, and environmental destruction of fish oil.
Recommended dose: 250-500mg combined DHA+EPA daily from algal oil. Prioritize DHA — it's the harder one to get. For more on the omega-3 pathway, see our Omega-3 Fatty Acids for Vegans guide.
Iodine is essential for thyroid function. Dairy is a major iodine source in Western diets (not because milk is naturally rich in iodine, but because iodine-based sanitizers are used on dairy equipment and iodine is added to cattle feed). When you remove dairy, your iodine intake can drop significantly.
Seaweed is the richest plant source of iodine, but intake is unpredictable — nori contains relatively little (about 16µg per sheet), while kombu can contain dangerously high levels (up to 2,984µg per gram). Iodized salt provides about 45µg per 1/4 teaspoon, but many people use non-iodized sea salt or Himalayan pink salt, which contain negligible iodine.
Recommended dose: 150µg daily from a supplement or iodized salt, unless you regularly consume moderate amounts of seaweed. Do not exceed 1,100µg daily — excess iodine can paradoxically suppress thyroid function.
ℹ️ Kelp tablets: proceed with caution
Zinc is present in many plant foods — pumpkin seeds, lentils, chickpeas, cashews, oats, hemp seeds — but phytic acid in whole grains and legumes inhibits zinc absorption by up to 50%. The Institute of Medicine recommends that people consuming high-phytate diets may need up to 50% more zinc than the standard RDA.
For most vegans eating a varied diet with good food preparation practices (soaking, sprouting, fermenting — all of which reduce phytic acid), supplementation isn't strictly necessary. But if you notice symptoms of zinc deficiency — impaired wound healing, frequent colds, hair loss, or loss of taste — a supplement of 15-30mg of zinc gluconate or zinc picolinate daily can help.
Preformed vitamin A (retinol) is found only in animal foods, but your body converts beta-carotene from plant foods into retinol efficiently. A single medium sweet potato provides over 200% of your daily vitamin A needs. Carrots, spinach, kale, butternut squash, and cantaloupe are all excellent sources. Unless you have a rare genetic variant that impairs beta-carotene conversion (BCMO1 gene polymorphism), you don't need a vitamin A supplement on a varied vegan diet.
Vitamin K1 (phylloquinone) is abundant in green leafy vegetables — a cup of cooked kale provides over 1,000% of the daily requirement. Vitamin K2 (menaquinone) is produced by gut bacteria and is also found in fermented foods like natto, sauerkraut, and tempeh. Most vegans who eat their greens and occasional fermented foods have excellent vitamin K status without supplementation.
Despite the persistent myth, vegans are no more likely to be iron deficient than omnivores. A 2018 systematic review in Critical Reviews in Food Science and Nutrition found no significant difference in iron deficiency anemia rates between vegetarians/vegans and meat-eaters. Plant iron (non-heme) is less bioavailable, but the body upregulates absorption when stores are low, and pairing iron-rich foods with vitamin C dramatically increases absorption. See our Iron on a Vegan Diet article for details.
Rather than taking a dozen individual pills, many vegans simplify with this approach:
This covers your bases with just two daily supplements. Get blood work done annually to check B12, vitamin D, iron/ferritin, and thyroid function (TSH). Adjust based on your individual results, not internet advice.
💡 Timing matters
For a complete overview of vegan nutrition beyond supplements, see our Complete Vegan Nutrition Guide guide.
How much protein you actually need, the best plant-based sources, and how to hit your targets effortlessly.
The definitive guide to Vitamin B12 for vegans: why you need it, how much, and which supplements work.
How to get enough iron on a plant-based diet, the role of Vitamin C, and which foods are best.
Disclaimer: The information in this article is for educational purposes only and does not constitute medical or nutritional advice. Always consult a qualified healthcare professional before making significant changes to your diet, especially regarding supplementation and nutrient intake.