Why do vegans take so many supplements? A guide to essential nutrients

October 20, 2025 •

5 min read

Approximately 40-50% of vegans who do not supplement show signs of vitamin B12 deficiency, a critical nutrient not reliably found in plants. This fact highlights a primary reason why vegans take so many supplements to ensure optimal health and prevent nutrient gaps that naturally occur on a plant-based diet.

Quick Summary

Vegans often need supplements to address specific nutrients like vitamin B12, vitamin D, iron, and omega-3s, which are less abundant or have lower bioavailability in plant foods. Supplementation is a reliable strategy for preventing deficiencies on a plant-based diet.

Key Points

B12 is essential for vegans: This vitamin is not reliably available in plant-based foods, making consistent supplementation or intake of fortified foods necessary for nervous system and red blood cell health.
Vitamin D requires extra attention: While sunlight is a primary source, vegans often need to use fortified foods or vegan D3 supplements, especially during darker months, as plant-based sources are limited.
Iron absorption is less efficient: Non-heme iron from plants is less bioavailable than animal iron. Vegans can enhance absorption by pairing iron-rich foods with vitamin C.
Algae-based Omega-3s are recommended: The body's conversion of plant-based ALA to active DHA and EPA is inefficient, so an algae oil supplement is the most reliable source for these crucial fatty acids.
Phytates impact mineral absorption: Compounds in many plant foods, called phytates, can inhibit the absorption of minerals like zinc and iron. Soaking or sprouting can help, but supplementation may still be needed.
Iodine intake is often unpredictable: The iodine content of plant foods varies based on soil quality, making a reliable intake difficult to achieve without iodized salt or a supplement.
Supplements are a proactive health choice: Taking supplements for key nutrients is not a sign of a deficient diet but rather a strategic and reliable way for vegans to ensure comprehensive nutrition.

A well-planned vegan diet is rich in a wide array of vitamins, minerals, and antioxidants, offering numerous health benefits. However, certain key nutrients are either not present in plant-based foods or are less bioavailable, meaning the body does not absorb and use them as efficiently. In this modern era, relying solely on food to meet all nutritional needs can be precarious, regardless of diet. For vegans, strategic and consistent supplementation is a smart, evidence-based approach to ensure optimal health and fill potential nutrient gaps.

The vitamin B12 imperative

Vitamin B12 is arguably the most crucial supplement for a vegan diet because it is not reliably supplied from unfortified plant foods. This essential nutrient is produced by microorganisms and is primarily found in animal products. Its vital functions include the formation of red blood cells, DNA synthesis, and maintaining a healthy nervous system.

Without a reliable source, deficiency can lead to severe health issues, including megaloblastic anemia and irreversible nervous system damage. The Vegan Society and other health bodies emphasize that consistent intake from fortified foods (such as plant milks and nutritional yeast) or a daily or weekly supplement is non-negotiable for vegans.

Vitamin D: The 'sunshine vitamin'

While the body can produce vitamin D from sun exposure, many factors—like geographical location, skin tone, and season—can limit production. Few foods, animal-based or plant-based, are naturally good sources of vitamin D. While some mushrooms grown under UV light can provide vitamin D2, the form found in animal products, D3, is often more bioavailable.

For vegans, ensuring adequate vitamin D intake requires a strategy. Options include relying on fortified foods, spending adequate time in the sun, or taking a vegan-friendly D3 supplement derived from lichen. Many health authorities recommend supplementation for everyone during winter months.

Navigating the complexities of iron

Iron is vital for producing red blood cells and transporting oxygen throughout the body. The iron found in plant foods (non-heme iron) is not as easily absorbed as the heme iron found in animal products. This lower bioavailability is compounded by plant compounds like phytates and tannins, which can inhibit absorption.

For vegans, particularly women and athletes, ensuring sufficient iron intake is a priority. Strategies to maximize iron absorption from plant sources include:

Pairing iron-rich foods with vitamin C sources (e.g., lemon juice on spinach salad).
Soaking and sprouting grains and legumes to reduce phytate content.
Cooking in cast-iron cookware can also increase iron content in food.

While many vegans can meet their needs through a varied diet, supplementation may be necessary, especially for those with low iron stores.

The need for long-chain Omega-3s

The omega-3 fatty acids EPA and DHA are crucial for heart and brain health. While plant foods contain alpha-linolenic acid (ALA), which the body can convert into EPA and DHA, this conversion process is notoriously inefficient. As a result, studies consistently show lower levels of DHA and EPA in vegans.

To ensure optimal intake, vegans should consume ALA-rich foods like walnuts, chia seeds, and flaxseeds. However, a daily algae-based supplement containing preformed DHA and EPA is widely recommended, particularly for pregnant and breastfeeding women, and for those with increased needs.

Calcium: More than just dairy

Calcium is essential for strong bones and proper muscle and nerve function. While numerous plant foods contain calcium, its bioavailability varies significantly due to compounds like oxalates. Vegans who consume less than 525 mg of calcium daily may face a higher risk of bone fractures.

Fortified plant milks, tofu set with calcium sulfate, and low-oxalate leafy greens are excellent vegan sources. However, supplements are a reliable way to ensure the recommended daily intake is met, especially if dietary intake falls short.

Other nutrients to consider

Zinc: Phytates in plant foods also interfere with zinc absorption. Although sources like legumes, nuts, and seeds contain zinc, vegans and vegetarians tend to have lower overall levels. A supplement might be beneficial, especially for those with lower zinc intake.
Iodine: The iodine content of plants is inconsistent, as it depends on the soil they are grown in. Vegans, who do not consume dairy or fish, often have lower iodine levels. Regular use of iodized salt or a supplement is recommended to maintain healthy thyroid function.

Nutrient Comparison: Vegan vs. Omnivore Sources


Nutrient	Primary Omnivore Sources	Primary Vegan Sources	Absorption and Conversion	Supplementation Note
Vitamin B12	Meat, dairy, eggs	Fortified foods, supplements	Reliable only from fortified sources; not naturally in plants	Essential. The most critical supplement for all vegans.
Vitamin D	Fatty fish, eggs, fortified dairy	Sunlight, UV-exposed mushrooms, fortified foods	D2 from plants can be less bioavailable than D3 from animals	Often recommended. Vegan D3 from lichen is available.
Iron	Red meat (heme iron)	Legumes, dark leafy greens, nuts (non-heme iron)	Non-heme iron is less bioavailable; absorption is improved with vitamin C	Beneficial. May be needed to avoid low iron stores.
Omega-3s (EPA/DHA)	Oily fish	ALA from seeds, nuts (low conversion)	Conversion from ALA to EPA/DHA is inefficient in the body	Strongly recommended. Algae-based supplements provide preformed DHA/EPA.
Calcium	Dairy products	Fortified milks, calcium-set tofu, leafy greens	Absorption can be inhibited by oxalates in some plants	May be necessary. Especially important for those with lower daily intake.
Zinc	Meat, dairy	Legumes, nuts, seeds	Phytates in plant foods can significantly impair absorption	Consider supplementing. Often recommended to ensure adequate levels.
Iodine	Fish, dairy	Iodized salt, seaweed	Varies widely based on soil content	Often needed. Using iodized salt or a supplement is the most reliable method.

The value of a planned approach

Ultimately, a vegan diet is not inherently deficient, but it does require more conscious planning to ensure all nutritional needs are met. Supplementation is not a sign of a flawed diet; rather, it is a proactive step that recognizes the nutritional realities of modern food systems. Even omnivores often benefit from supplements like vitamin D due to limited sunlight or B12 due to age or absorption issues. By taking targeted supplements, vegans can ensure their bodies receive these key nutrients in a reliable, absorbable form, allowing them to reap the full health benefits of a plant-based lifestyle.

For more information on vitamin B12, consult the guidelines provided by The Vegan Society.

Frequently Asked Questions

Vitamin B12 is crucial for maintaining a healthy nervous system and for the formation of red blood cells. Since it is produced by microorganisms and not reliably found in plants, vegans must obtain it from fortified foods or a supplement to prevent deficiency.

Sunlight is a primary source of vitamin D, but factors like season, location, and skin tone affect production. Vegans should not rely on sun alone, especially in winter. Fortified foods and vegan D3 supplements are recommended.

Vegans can improve the absorption of non-heme iron from plant foods by pairing them with sources of vitamin C. Squeezing lemon juice on a spinach salad or eating bell peppers with beans are effective strategies.

Since the body's conversion of plant-based ALA to active DHA and EPA is inefficient, an algae-based omega-3 supplement is the most reliable way for vegans to ensure optimal levels, particularly for brain and heart health.

Fortified foods, such as plant milks and cereals, can contribute significantly to a vegan's nutritional intake for certain vitamins. However, because content can vary, supplements often provide a more consistent and reliable dose to ensure needs are fully met.

Phytates, compounds found in legumes, nuts, and whole grains, can inhibit the absorption of minerals like zinc and iron. Soaking, sprouting, or fermenting foods can help reduce phytate content.

While many plant foods contain calcium, factors like oxalates can inhibit its absorption. Vegans who have a low calcium intake are at higher risk for bone fractures, making fortified foods or supplements important for bone health.

The most common and most serious deficiency in unsupplemented vegans is vitamin B12, as it is not reliably available in plant-based foods.