Vegan Diet Deficiencies: Common Nutritional Gaps and How to Prevent Them

Plant-based diets offer many health benefits. However, research suggests that without careful planning, it is easy to develop vegan diet deficiencies and fall short of several critical nutrients (Akinwumi et al., 2025). A plant-based diet should be strategic rather than casual.

What Are the Most Common Vegan Diet Deficiencies?

The most common gaps in vegan and plant-based diets discussed in this review include vitamin B12, iron, calcium, and vitamin D. Other nutrients, such as iodine, may also require attention in some plant-based diets depending on food choices.

The review linked nutritional deficiencies in iron, vitamin B12, calcium, and vitamin D in plant-based diets to higher long-term risks of iron-deficiency anemia and osteoporosis. The iron in plant foods is harder for the body to absorb (see my guide to vegan iron-rich foods). Low levels of iron and B12 can reduce the production of healthy red blood cells. Insufficient calcium and vitamin D can weaken bones (Akinwumi et al., 2025).

This suggests that people following plant-based diets should pay close attention to these nutrients. They should actively include them in their daily diet, for example, by choosing fortified foods, combining foods to improve absorption (e.g., iron + vitamin C), and by supplementing.

Can You Have a Vitamin B12 Deficiency in a Vegan Diet with a Normal Blood Test?

Yes, it is possible to have a functional vitamin B12 deficiency even if serum B12 levels are within the normal range.

Vitamin B12 stores can fall before serum levels drop below the reference range. During this time, cellular function can be affected, symptoms may start, and only later do blood tests show the deficiency. (O’Leary and Samman, 2010).

Can Other Nutrient Deficiencies Be Missed on Routine Blood Tests?

Yes. Most routine tests measure what is circulating in the blood rather than what is within cells or tissues. As a result, the results may not reflect early-stage deficiencies.

Why are nutrient deficiency symptoms often overlooked?

Early signs of deficiency can be easily overlooked, as the symptoms may be attributed to other causes. For example, it is easy to attribute fatigue, brain fog, and restless legs to hormones or stress.

Who Is Most at Risk of Vegan Diet Deficiencies?

In general, people who experience greater iron losses, bone turnover, or recovery demands are at higher risk. This includes:

• Women who menstruate
• Physically active or athletic people
• Anyone over 40
• Anyone following a plant-based diet long-term
• Not supplementing vitamin B12 or vitamin D

The reason is that their nutrient needs are higher, so they have less scope to fall short. (Akinwumi et al., 2025). 

What are the long-term health risks of unaddressed deficiencies?

Chronic low iron can lead to:

• Chronic fatigue
• Lower energy levels and reduced concentration
• Problems with memory and thinking
• Increased stress on the heart
• A weaker immune system and disrupted hormone balance
• Reduced muscle strength and bone health
• Reduced fertility
• More health challenges in later life (Xu et al., 2012)

Untreated B12 deficiency can lead to:

• Damage to the brain and nerves
• Difficulties with concentration and mood
• Increased risk of heart problems
• Fertility problems and pregnancy complications
• Declines in health as you age (Shipton and Thachil, 2015)

Inadequate calcium and vitamin D intake over time can lead to:

• Reduced bone strength over time 
• Higher risk of osteoporosis and fractures as you get older (Akinwumi et al., 2025)

While this review focused primarily on micronutrient deficiencies, similar long-term risks can arise when overall protein and energy intake are consistently low. See my article on plant protein vs animal protein for a deeper look at how protein source influences ageing and metabolic health.

Chronic low protein and energy intake can lead to:

• Reduced muscle mass and strength
• Slower recovery
• Higher injury risk
• Earlier frailty as people move into midlife and older age (Granic et al., 2018)

Are plant-based diets safe without strategic planning?

Following a plant-based diet without adequate planning may increase the risk of nutritional deficiencies over time. With informed choices, appropriate supplementation, and regular monitoring, plant-based diets can support both short and long-term health. At a minimum, a well-planned plant-based diet should incorporate:

• Vitamin B12 (through supplements or reliably fortified foods)
• Iron, with attention to absorption (for example, pairing with vitamin C)
• Calcium (via fortified plant milks, yoghurts, or calcium-set tofu)
• Vitamin D, particularly in low-sun locations
• Adequate protein intake, with sufficient quantity and quality

 Key Takeaways

• Research shows that plant-based diets are associated with a lower risk of chronic disease such as cardiovascular disease, obesity, type 2 diabetes, and some cancers.
• However, poorly planned plant-based diets may increase the risk of inadequate intake of key nutrients, particularly vitamin B12, iron, calcium, and vitamin D.
• Early-stage deficiencies may not always be detected through routine blood tests. Symptoms can develop before laboratory results highlight the problem.
• Certain groups may be at higher risk of nutrient deficiencies, including people who menstruate, individuals with high levels of physical activity, older adults, and those who have followed plant-based diets for many years. These individuals may benefit from periodic monitoring of nutrient status.
• Long-term untreated deficiencies can affect neurological, cardiovascular, skeletal, and reproductive health.
• With intentional dietary planning, appropriate supplementation, and attention to nutrient intake, vegan and vegetarian diets can support long-term health.

Frequently Asked Questions

References

1. Akinwumi FE et al. (2025). Risk of osteoporosis and anemia in plant-based diets: A systematic review of nutritional deficiencies and clinical implications. Cureus. https://doi.org/10.7759/cureus.88461
2. O’Leary F, Samman S. (2010). Vitamin B12 in health and disease. Nutrients, 2(3), 299–316. https://doi.org/10.3390/nu2030299
3. Xu J et al. (2012). Impaired iron status in aging research. International Journal of Molecular Sciences, 13(2), 2368–2386. https://doi.org/10.3390/ijms13022368
4. Shipton MJ, Thachil J. (2015). Vitamin B12 deficiency: A 21st century perspective. Clinical Medicine, 15(2), 145–150. https://doi.org/10.7861/clinmedicine.15-2-145
5. Granic A et al. (2018). Low protein intake, muscle strength and physical performance in the very old: The Newcastle 85+ Study. Clinical Nutrition, 37(6), 2260–2270. https://doi.org/10.1016/j.clnu.2017.11.005
6. Neufingerl N, Eilander A. (2021). Nutrient intake and status in adults consuming plant-based diets compared to meat-eaters: A systematic review. Nutrients, 14(1), 29.