What Vitamin is Deficient in a Vegan Diet? The Full Guide

January 3, 2026 •

4 min read

According to the National Institutes of Health, vegans are at a higher risk of vitamin B12 deficiency because natural food sources of this essential nutrient are almost exclusively animal-based. A well-planned vegan diet requires careful attention to specific vitamins and minerals to ensure complete nutritional adequacy.

Quick Summary

A strict vegan diet eliminates all animal products, removing the primary sources of vitamin B12, making it the most critical deficient vitamin. Vegans also need to monitor other nutrients like vitamin D, calcium, iron, and omega-3 fatty acids, which can be less bioavailable or less common in plant-based sources. Careful meal planning, fortified foods, and supplements are essential to avoid potential long-term health risks associated with these deficiencies.

Key Points

Vitamin B12 is the primary concern for vegans due to its absence from unfortified plant-based foods, requiring supplementation or fortified food consumption.
Other critical nutrients for vegans include vitamin D, iron, calcium, iodine, zinc, and omega-3s, which may have lower bioavailability or availability in plant-based diets.
Fortified foods and supplements are reliable sources for nutrients like B12 and D, but labels should be checked carefully.
Enhance iron absorption by pairing iron-rich plant foods with sources of vitamin C.
Regular blood tests are recommended to monitor micronutrient levels and ensure a nutritionally complete diet.
Algae-based supplements are an excellent source for long-chain omega-3s (EPA and DHA), which are difficult to obtain from other vegan sources.
Pregnant or breastfeeding vegans and growing children need especially careful dietary planning and medical supervision due to increased nutrient requirements.

Why Vitamin B12 is the Most Crucial Concern for Vegans

Vitamin B12, or cobalamin, is a water-soluble vitamin vital for nerve function, red blood cell formation, and DNA synthesis. Unlike other vitamins, B12 is produced by microorganisms, not plants, and accumulates in the animal products humans typically consume. This makes unfortified plant-based foods an unreliable source, putting vegans who do not supplement at high risk for deficiency.

Deficiency can lead to serious health problems, including megaloblastic anemia, which causes fatigue and weakness, and irreversible nerve damage. Symptoms can manifest gradually, making it difficult to detect early without regular monitoring. Infants breastfed by B12-deficient vegan mothers are particularly vulnerable and can suffer severe, sometimes permanent, neurological damage.

Reliable Vegan Sources of Vitamin B12

To prevent deficiency, vegans must obtain B12 from reliable sources. These include:

Fortified foods: Many plant-based products, including nutritional yeast, plant milks (like soy and oat), and some breakfast cereals, are fortified with B12. Checking the product label is crucial to ensure adequate fortification.
Supplements: Vitamin B12 supplements are a dependable and often necessary source, especially for those who do not regularly consume fortified foods. Options include daily, sublingual, or weekly high-dose supplements.

Other Nutrients to Monitor on a Vegan Diet

While B12 is the most commonly cited, several other vitamins and minerals can be challenging to obtain sufficient amounts of on a vegan diet without careful planning and potentially supplementation. These include:

Vitamin D: Primarily synthesized by the body from sunlight exposure, vitamin D is crucial for bone health and calcium absorption. Dietary sources are limited, with animal products like fatty fish and eggs being common. Vegans must rely on sun exposure, fortified foods, and supplements.
Calcium: Essential for healthy bones and teeth, calcium intake can be lower in vegans, increasing the risk of bone fracture. Plant-based sources exist, but absorption can be hindered by oxalates and phytates found in some plants. Fortified plant milks and calcium-set tofu are excellent choices.
Iron: Plant-based iron (non-heme) is not as readily absorbed as the heme iron found in meat. While vegan diets can be high in iron, poor absorption can lead to lower iron stores. Consuming vitamin C with iron-rich plant foods like lentils and leafy greens significantly boosts absorption.
Iodine: This mineral is vital for thyroid function. Vegans who avoid iodized salt and rely on plant-based milks that are often not fortified can have low intake. Using iodized salt or taking an iodine supplement is recommended.
Zinc: Involved in immune function, cell growth, and metabolism, zinc absorption can be reduced by phytates in plant foods. While many plant foods contain zinc (legumes, nuts, seeds), supplementation may be necessary for some vegans, especially if they experience symptoms of deficiency.
Omega-3 Fatty Acids: The essential long-chain omega-3s, EPA and DHA, are primarily found in fish. While vegans can get ALA from sources like flax and chia seeds, the body's conversion to EPA and DHA is inefficient. Algae-based supplements are a reliable way to ensure adequate intake.

Comparison of Essential Nutrients: Vegan vs. Omnivore Diet


Nutrient	Primary Omnivore Sources	Primary Vegan Sources	Key Challenges for Vegans	Supplementation Strategy
Vitamin B12	Meat, dairy, eggs	Fortified foods, nutritional yeast, supplements	Not naturally found in plants	Essential, via fortified foods or supplements.
Vitamin D	Oily fish, egg yolks, fortified dairy	Sunlight, fortified plant milks, UV-exposed mushrooms	Limited natural dietary sources; depends on sun exposure	Advised, especially in winter or with limited sun.
Calcium	Dairy products	Fortified plant milks/yogurts, calcium-set tofu, leafy greens	Lower bioavailability due to phytates/oxalates	Consider supplement if intake from food is low.
Iron	Red meat, poultry, fish	Lentils, beans, leafy greens, fortified cereals	Non-heme iron is less easily absorbed	Pair plant-based iron with vitamin C to enhance absorption.
Iodine	Dairy, seafood, iodized salt	Iodized salt, seaweed, fortified foods	Lower intake can lead to thyroid issues	Use iodized salt or take a supplement.
Zinc	Meat, dairy, seafood	Legumes, nuts, seeds, tofu	Phytates in plants reduce absorption	May need a supplement to ensure adequacy.
Omega-3s (EPA/DHA)	Oily fish	Algae-based supplements	Inefficient conversion from plant-based ALA	Take an algae-based DHA/EPA supplement.

Conclusion

While a well-planned vegan diet can be healthful and nutritionally adequate, paying special attention to key micronutrients is critical. The most prominent deficiency risk is vitamin B12, which is not reliably present in plant foods, making supplementation essential. Beyond B12, careful consideration should be given to nutrients like vitamin D, calcium, iron, iodine, zinc, and omega-3 fatty acids. By consuming a varied diet rich in fortified foods and using targeted supplements where necessary, vegans can effectively mitigate these risks and enjoy a nourishing, plant-based lifestyle. Regular blood tests are also highly recommended to monitor levels and adjust intake as needed.

For more detailed nutritional guidelines, consult resources from reputable health organizations like the National Institutes of Health.

Frequently Asked Questions

The most common and significant vitamin deficiency in a vegan diet is vitamin B12. Since this vitamin is naturally produced by microorganisms and found almost exclusively in animal products, vegans must rely on fortified foods or supplements to meet their needs.

Vegans can get enough vitamin B12 by regularly consuming fortified foods like plant-based milks, nutritional yeast, and some cereals, or by taking a daily or weekly B12 supplement.

Yes, vegans can be at a higher risk of low vitamin D because primary dietary sources like fatty fish and eggs are excluded. Adequate sun exposure is key, but supplementation is often advised, especially during winter months.

Vegans need to focus on a variety of calcium-rich and fortified foods like fortified plant milks, calcium-set tofu, and leafy greens. A supplement may be needed if intake from these sources is insufficient, especially since calcium absorption from plant sources can be less efficient.

To increase iron absorption from plant-based (non-heme) sources, vegans should pair iron-rich foods such as lentils, chickpeas, and leafy greens with foods high in vitamin C, like bell peppers or citrus fruits.

While flaxseeds and chia seeds provide the shorter-chain omega-3 ALA, the most effective vegan sources for the longer-chain EPA and DHA are algae-based supplements. Walnuts and hemp seeds also contain ALA.

Yes, some studies suggest that a significant number of vegans may be zinc-deficient due to lower intake and reduced absorption from plant foods containing phytates. Regular intake of zinc-rich foods like legumes, nuts, and seeds is important, and a supplement may be beneficial.