Which Nutrient Would the Vegan Patient Likely Have Nutritional Deficits In?

December 5, 2025 •

5 min read

According to a systematic review published in Nutrients, vegans often have lower levels of key micronutrients like vitamin B12, vitamin D, and iodine compared to meat-eaters. The primary nutritional concern for most vegan patients is vitamin B12, as it is almost exclusively found in animal products. Understanding and addressing these specific nutritional deficits is crucial for maintaining optimal health on a plant-based diet.

Quick Summary

This article explores the specific nutrient deficiencies common in vegan patients, focusing primarily on vitamin B12 and other critical vitamins and minerals. It details why these deficits occur and outlines practical strategies for supplementation and dietary planning to ensure a well-balanced vegan diet.

Key Points

Vitamin B12 is the primary concern: Vegans must supplement or eat fortified foods for B12, as it's not reliably available in unfortified plant foods.
Iron absorption is less efficient: Non-heme iron from plant sources is less bioavailable, necessitating strategic food combinations with vitamin C to enhance absorption.
Calcium intake can be low: While calcium is in many plant foods, compounds like oxalates can reduce absorption, making fortified products and supplements important.
Omega-3s require special attention: Conversion of plant-based ALA to EPA and DHA is inefficient; algae-based supplements are a direct source for these crucial fats.
Iodine and Zinc need planning: Deficits can occur due to lower intake or bioavailability, highlighting the need for iodized salt, seaweed, and zinc-rich foods.
Comprehensive blood testing is advised: Reliable assessment of B12 status should include MMA testing, as high folate levels can mask deficiency symptoms.
Risks for vulnerable populations are higher: Pregnant and breastfeeding women and children on vegan diets require heightened vigilance to prevent severe deficiencies.

The Primary Concern: Vitamin B12

Vitamin B12, or cobalamin, is arguably the most critical nutrient for any vegan patient to monitor. It is essential for nerve function, DNA synthesis, and red blood cell formation. Unlike other nutrients, vitamin B12 is produced by microorganisms and is not reliably present in unfortified plant foods. While some plant sources like algae have been anecdotally mentioned, they are not considered reliable sources of the active form of B12. The body can store vitamin B12 in the liver for several years, which is why a deficiency can take a long time to manifest after transitioning to a vegan diet. However, once stores are depleted, symptoms can range from fatigue and weakness to severe and irreversible neurological damage.

Reliable Sources of Vitamin B12 for Vegans

To prevent deficiency, vegans must consume B12 from fortified foods or supplements. Reliable vegan sources include:

Fortified Plant Milks: Many soy, almond, and oat milks are fortified with B12. Reading labels is essential.
Fortified Cereals: Certain breakfast cereals offer a significant percentage of the daily value.
Nutritional Yeast: Often a favorite of the vegan community, nutritional yeast is a reliable and tasty way to get B12, provided it is fortified.
B12 Supplements: Taking a daily supplement with at least 10 mcg or a weekly supplement of 2000 mcg is a widely recommended and highly effective strategy.

Other Potential Nutritional Deficits

Beyond vitamin B12, other nutrients may require careful planning and, in some cases, supplementation for vegan patients. The bioavailability of minerals from plant-based foods can be lower due to compounds like phytates and oxalates.

Iron

Iron is vital for oxygen transport and energy production. While vegan diets are often rich in iron from sources like lentils, beans, and spinach, this is non-heme iron, which is less easily absorbed than the heme iron found in meat.

Boosting Absorption: Pairing iron-rich plant foods with vitamin C-rich foods (e.g., bell peppers with beans or strawberries with cereal) significantly enhances non-heme iron absorption.
Inhibitors: Substances like tannins in tea and coffee can inhibit iron absorption, so it is best to avoid consuming these beverages with iron-rich meals.

Calcium and Vitamin D

These two nutrients are crucial for bone health, and vegans are often at a higher risk for insufficient intake. While leafy greens, almonds, and fortified plant milks are good sources of calcium, the presence of oxalates and phytates in some greens can hinder absorption. Vitamin D is also a concern, as it is primarily obtained through sun exposure or animal products. Many vegans may need to rely on fortified foods or supplements, especially in winter months.

Omega-3 Fatty Acids

The long-chain omega-3s, EPA and DHA, are primarily found in fatty fish. While vegans get ALA from plant sources like flaxseeds and walnuts, the body's conversion rate to EPA and DHA is often very low. This can impact brain and heart health. Algae-based DHA and EPA supplements are an excellent, direct source of these essential fats for vegans.

Iodine and Zinc

Iodine is critical for thyroid function, and vegans often have lower intake due to avoiding fish and dairy. Using iodized salt or consuming fortified plant-based products can help. Zinc is important for immune function and wound healing. Although present in legumes, nuts, and seeds, absorption can be inhibited by phytates.

Comparison of Nutrients: Animal vs. Plant-Based Sources

To highlight the differences in nutrient bioavailability, the following table compares key nutrients from animal-derived versus typical plant-based sources.


Nutrient	Primary Animal Source	Primary Plant Source	Bioavailability Factor
Vitamin B12	Meat, dairy, eggs	Fortified foods, supplements	High (animal); Requires fortification (plant)
Iron	Heme iron (meat)	Non-heme iron (legumes, leafy greens)	Higher (animal); Lower (plant, improved with vitamin C)
Calcium	Dairy products	Fortified milks, calcium-set tofu, greens	High (animal); Lower in some greens due to oxalates
Omega-3s (EPA/DHA)	Oily fish	Algae-based supplements	Direct source (animal); Conversion from ALA is inefficient (plant)
Vitamin D	Fatty fish, fortified dairy	Fortified milks, sun exposure, mushrooms	Direct source (animal); Less bioavailable without fortification (plant)

Long-Term Health Implications of Deficits

Untreated nutritional deficits in a vegan patient can lead to serious long-term health consequences.

Neurological Damage: A severe and prolonged vitamin B12 deficiency can result in irreversible nerve damage, memory loss, and cognitive decline. This is particularly concerning for infants breastfed by B12-deficient mothers.
Anemia: Iron deficiency is the most common nutritional deficiency globally, and the reduced bioavailability of non-heme iron can increase a vegan patient's risk of developing anemia. Symptoms include chronic fatigue, weakness, and impaired cognitive function.
Bone Health: Low calcium and vitamin D intake, along with the potential for lower bioavailability, can lead to decreased bone mineral density and an increased risk of fractures, especially in older adults.
Thyroid Function: Chronic iodine deficiency can lead to hypothyroidism, which negatively impacts metabolism, brain development, and overall energy levels.

Conclusion

While a well-planned vegan diet can be nutritionally adequate and offer numerous health benefits, it requires careful attention to a few key nutrients. Vegan patients are most likely to have deficits in vitamin B12, a nutrient almost exclusively found in animal products. Other potential deficits include iron, calcium, vitamin D, omega-3 fatty acids, iodine, and zinc due to bioavailability issues or limited plant sources. By utilizing fortified foods, strategic food pairing, and necessary supplementation, these nutritional gaps can be effectively bridged. For any vegan patient, regular monitoring and professional guidance are recommended to ensure a balanced and healthy plant-based lifestyle.

The Vegan Society's Guide to B12

The Vegan Society offers a wealth of information on nutrient intake for those on a plant-based diet, with a strong focus on the importance of vitamin B12 supplementation. For detailed guidance, including dosage recommendations, their resource, "What Every Vegan Should Know About Vitamin B12," is highly authoritative. Vegan Health: Iron

Essential Advice for Clinicians

When a vegan patient presents with symptoms, healthcare professionals should immediately consider a full nutritional panel to check for potential deficits. Focusing solely on common issues can lead to missed diagnoses. Clinicians should specifically assess vitamin B12 status using reliable tests like MMA testing, as serum B12 levels can be unreliable, especially if the patient consumes analogues from unfortified sources like certain algae.

This holistic approach ensures that any underlying deficiencies are addressed, providing the patient with the best possible care and support for their dietary choices. Educational materials and referrals to a registered dietitian specializing in plant-based nutrition can be invaluable tools for both the patient and the healthcare provider.

Frequently Asked Questions

No, a well-planned and varied vegan diet can provide all necessary nutrients. However, without proper planning and attention to sources like fortified foods or supplements, deficiencies in vitamin B12, iron, calcium, and omega-3s are possible.

Vitamin B12 is produced by bacteria and found almost exclusively in animal products. Since vegans consume no animal products, they must rely on fortified foods, such as plant milks and cereals, or supplements to meet their needs and prevent deficiency.

While spinach and other leafy greens contain iron, it is non-heme iron, which is not as well-absorbed as heme iron from meat. Pairing spinach with a vitamin C source, like lemon juice or bell peppers, can significantly improve absorption.

Since the conversion of plant-based ALA to the vital EPA and DHA is inefficient, the most reliable method for vegans to get these long-chain omega-3s is through algae-based supplements. Plant sources like flaxseeds still provide beneficial ALA.

Vegans can ensure adequate calcium by consuming fortified plant milks and yogurts, calcium-set tofu, and low-oxalate greens like kale. A supplement may be necessary, and sufficient vitamin D is also vital for proper calcium absorption.

Most vegans need to take a vitamin B12 supplement, as it is not reliably found in plant foods. For other nutrients like vitamin D, omega-3s, and iodine, supplementation depends on dietary variety, sun exposure, and careful planning.

Vitamin D is essential for absorbing calcium and is primarily synthesized from sun exposure or found in fortified products. Vegans may be at a higher risk of deficiency, especially in regions with limited sunlight, making fortified foods and supplements important.