Vegan diets can provide many health benefits but commonly require attention to several micronutrients that are less available or less bioavailable in plant foods. Winston J. Craig, Loma Linda University School of Public Health, has reviewed evidence showing that vitamin B12, iron, zinc, calcium, vitamin D, iodine, and long-chain omega-3 fatty acids are the nutrients most often of concern for people following strict vegan diets. The Office of Dietary Supplements, National Institutes of Health, provides detailed fact sheets corroborating these concerns and explaining physiological roles and signs of deficiency.
Key nutrients at risk
Vitamin B12 is produced by microorganisms and is naturally abundant in animal products but absent from unfortified plant foods. Deficiency can cause irreversible neurological damage and megaloblastic anemia, making B12 supplementation or consumption of reliably fortified foods essential for long-term vegans. Iron from plant sources is non-heme iron, which is less well absorbed than heme iron from meat; poor iron status can cause fatigue and impaired cognitive function. Zinc absorption is reduced by phytates in legumes and whole grains, which can affect immune function and wound healing if intake is inadequate. Calcium and vitamin D are central to bone health; some plant sources supply calcium but habitual low intake, limited sun exposure, or absence of fortified foods can raise the risk of lower bone mineral density. Iodine depends heavily on local soil and salt-fortification practices; insufficient iodine impairs thyroid function and can affect fetal neurodevelopment. Long-chain omega-3 fatty acids EPA and DHA are scarce in plants, and conversion from plant-based ALA is limited, which may influence cardiovascular and neurocognitive outcomes in certain life stages.
Causes, consequences, and context
Causes of these nutrient gaps include both absolute absence of certain nutrients in plant foods and lower bioavailability due to natural compounds in plants. Consequences vary by nutrient: neurological impairment for prolonged B12 deficiency, anemia and reduced work capacity from inadequate iron, skeleton fragility from insufficient calcium and vitamin D, and developmental risks from iodine shortfalls. Vulnerable groups include infants, children, adolescents, pregnant and breastfeeding people, and older adults, where the physiological demand and potential consequences are greater.
Cultural and territorial factors shape risk. In regions with routine food fortification and availability of fortified plant milks and nutritional yeast, deficiencies are less common. Conversely, communities relying on traditional unfortified staples or living in areas with iodine-poor soils face higher risk. Economic access to supplements and fortified products also influences outcomes. Environmentally, many choose vegan diets for sustainability reasons, but environmental benefits do not eliminate the need for targeted nutritional planning.
Practical prevention emphasizes deliberate dietary planning with attention to fortified foods and, when appropriate, supplementation under clinical guidance. Winston J. Craig, Loma Linda University School of Public Health, and the Office of Dietary Supplements, National Institutes of Health, both stress that well-planned vegan diets can be nutritionally adequate but require informed strategies to avoid these specific micronutrient shortfalls. Regular monitoring during life stages of higher need and culturally appropriate food policies that expand fortification can reduce population-level risk.