Do Vegans Actually Need Supplements? The 7 Nutrients Most Plant-Based Diets Miss

Vitamin B12 does not exist in any plant food in meaningful, bioavailable amounts. Full stop.* Algae, fermented foods, and certain mushrooms are sometimes cited as plant sources -- but the research consistently shows these contain B12 analogues that actually block absorption of true B12, making them potentially counterproductive.* B12 is produced exclusively by bacteria -- in nature, animals accumulate it by eating bacteria-contaminated food or water. Modern hygiene practices mean even those routes are largely closed to humans.*

B12 is essential for nerve function, DNA synthesis, and red blood cell formation.* Deficiency causes irreversible neurological damage, megaloblastic anemia, and fatigue -- and it develops silently over months to years because the body stores B12 in the liver.* By the time symptoms appear, the deficiency is often severe.* The Quadram Institute (2021) called it a "hidden epidemic" in vegan and vegetarian populations, with deficiency rates up to 62% in unsupplemented pregnant vegans.*

Plant foods do contain iron -- but almost exclusively as non-heme iron, the form the body absorbs at a fraction of the rate of heme iron from meat.* While heme iron from animal sources is absorbed at 15-35%, non-heme iron from plants is absorbed at only 2-20%, depending on what else is eaten alongside it.* Phytates in legumes and grains, polyphenols in tea and coffee, and calcium all further inhibit non-heme iron absorption.*

Vegans often consume adequate milligrams of iron on paper -- but their bodies absorb significantly less of it.* The result is that iron deficiency is roughly twice as common in vegetarian and vegan women as in omnivores.* Iron deficiency anemia causes fatigue, impaired immune function, poor exercise tolerance, and -- critically -- adverse outcomes in pregnancy.* The recommended intake for premenopausal women is 18mg/day; vegans are often advised to target 1.8x this amount due to the bioavailability gap.*

Plant foods provide ALA (alpha-linolenic acid) -- found in flaxseeds, chia seeds, and walnuts -- but the body must convert ALA into the biologically active forms DHA and EPA, which are the ones that actually do the work in the brain, cardiovascular system, and inflammatory pathways.* The problem: this conversion is extremely inefficient.* Research shows that humans convert only about 5-10% of ALA to EPA, and less than 1% to DHA.*

DHA is the primary structural fat in the brain and retina.* Low DHA is associated with cognitive decline, depression, and adverse neurodevelopmental outcomes in infants.* EPA drives the anti-inflammatory prostaglandin pathway.* Vegans consistently show significantly lower blood DHA and EPA levels than omnivores.* The only direct vegan sources of DHA and EPA are algae -- which is exactly where fish get theirs.* Algae-based omega-3 supplements bypass the conversion problem entirely.*

Iodine is largely absent from plant foods grown in iodine-depleted soils -- which covers most of inland agriculture worldwide.* The main dietary sources are seafood, dairy (where iodine enters via cattle feed and equipment sanitizers), and iodized salt. Vegans who avoid dairy and seafood and use non-iodized specialty salts are at high risk of iodine inadequacy.* The 2025 PubMed review specifically flagged iodine as a critical deficiency nutrient in vegan diets.*

Iodine is essential for thyroid hormone synthesis -- the hormones that regulate metabolism, growth, development, and energy production.* Iodine deficiency is the leading preventable cause of intellectual disability worldwide.* In adults, inadequate iodine causes hypothyroid symptoms: fatigue, weight gain, cold intolerance, and brain fog.* Sea vegetables (seaweed, sea moss) are among the richest natural plant sources of iodine.*

Vegans who avoid dairy lose their highest-density calcium source.* While plant foods like kale, bok choy, almonds, and fortified plant milks contain calcium, the bioavailability is highly variable.* High-oxalate vegetables like spinach and Swiss chard contain calcium but bind it tightly in oxalate complexes, reducing absorption to as low as 5%.* Phytates in wholegrains and legumes similarly inhibit calcium uptake.*

A 2020 meta-analysis in PLOS ONE found that vegans had significantly higher fracture rates than meat-eaters -- a finding attributed in part to lower calcium and vitamin D intake.* Calcium is the primary structural mineral in bone, and inadequate intake accelerates age-related bone density loss.* The risk is highest in women post-menopause, older adults, and children.* A 2025 EurekAlert meta-analysis of plant-based diets in children specifically highlighted calcium as the most concerning deficiency.* The RDA is 1,000-1,200mg/day for adults.*

Zinc is present in plant foods like legumes, nuts, seeds, and wholegrains -- but the same phytates that inhibit iron and calcium absorption also bind zinc.* The net effect is that plant-based zinc is significantly less bioavailable than zinc from meat and shellfish.* Some studies show vegans absorb up to 35% less zinc from their diet than omnivores eating comparable amounts.*

Zinc is required for immune cell function, wound healing, protein synthesis, testosterone production, thyroid hormone metabolism, and the activity of over 300 enzymes.* Zinc deficiency impairs immune response (making you more susceptible to illness), slows wound healing, and disrupts hormonal balance in both men and women.* The 2025 PubMed review on vegan nutritional deficiencies ranked zinc alongside B12 and iron as the highest-priority gaps.* Moringa is among the most zinc-dense plant foods available, alongside sea moss.*

Magnesium is technically present in many plant foods -- leafy greens, nuts, seeds, legumes, and wholegrains all contain it. Yet despite this, the majority of adults in developed countries are deficient, regardless of diet.* The USDA estimates that 48% of Americans consume less than the RDA for magnesium.* For vegans, the paradox is that while plant foods contain magnesium, soil depletion from modern agriculture and the phytate-binding problem mean that actual absorbed magnesium is frequently inadequate.*

Magnesium is a cofactor in over 300 enzymatic reactions -- including ATP synthesis (every cell's energy currency), protein synthesis, muscle contraction, nerve transmission, blood sugar regulation, and bone formation.* Deficiency presents as muscle cramps, poor sleep quality, anxiety, constipation, fatigue, and elevated blood pressure.* The form matters: magnesium oxide (cheap and common) has very low bioavailability.* Magnesium glycinate -- the chelated form -- has significantly higher absorption and is gentler on the GI tract.* Halea Life's Magnesium Glycinate 2500mg delivers the most bioavailable form at a clinically meaningful dose.*