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Vegan/Vegetarian Possible Deficiencies & Ways To Prevent Them

Written by Biljana Novkovic, PhD | Last updated:
Puya Yazdi
Medically reviewed by
Puya Yazdi, MD | Written by Biljana Novkovic, PhD | Last updated:

A healthy diet is balanced and provides you with adequate amounts of all the essential nutrients. As a vegan or vegetarian, you may be at a higher risk of certain nutritional deficiencies, while having a lower risk of others. In this post, we summarize the most important risks together with lab tests you can take to make sure your diet is well balanced and your health is optimal.

What to Monitor on a Vegetarian/Vegan Diet

We know your diet is often more than just what you eat – it’s a deliberate choice, a lifestyle, and a part of who you are. Food can be the key to achieving your health goals, improving your wellbeing, and making you feel like a part of a movement or community. Some people do better on animal-based diets, whereas others feel better on plant-based diets. This article will not debate the benefits of one vs. the other. Instead, it will focus on how to maximize your health on vegetarian and vegan diets.

Vegans and vegetarians are more at risk of certain nutritional deficiencies while being less at risk from others. In this post, we summarize the most important risks, and the tests you can take to make sure your diet is well balanced.

Important Nutrients

1) Iron

Iron deficiency is the most prevalent nutritional deficiency worldwide, caused mainly by insufficient dietary intake. Vegetarians and vegans are especially prone to iron deficiency because their diets lack heme iron [1, 2, 3]. Heme iron is only found in animal foods (meat, seafood, and poultry) and is easily absorbed. Non-heme iron, on the other hand, is found in plants and is less-well absorbed in our gut [4].

In addition, plants are often rich in phytates and polyphenols, compounds that inhibit iron absorption. Other nutrients that inhibit iron absorption are calcium and certain animal (found in dairy and eggs) and plant proteins (soy proteins) [4]. Studies suggest that because of all these factors, people on vegetarian diets may have iron absorption reduced by as much as 85% compared to people on omnivorous diets [5].

If you are on a vegetarian or a vegan diet, it’s a good idea to check your iron once in a while. Better yet, check your ferritin levels. While blood iron can be influenced by recent meals, ferritin is not and is, therefore, a better indicator of your body’s overall iron stores. Unsurprisingly, it is often lower than optimal in people on plant-based diets [6].

If your iron is low, here’s a good hack to help you increase it – vitamin C. Vitamin C (ascorbic acid) can bind iron and make sure it is well absorbed in your gut [4]. A simple way to get more vitamin C is to sprinkle some lemon juice to your salads. Also, cut back on tea, coffee, and dairy around your meals – all of these decrease the amount of iron your gut can absorb.

2) Zinc

Zinc is found in seafood, meat, eggs, and dairy. But it’s also found in whole grains, legumes, and seeds [7, 8]. So if it’s present in plant sources, why are vegetarians and vegans more likely to experience zinc deficiency [9, 10]?

Because plant sources also contain phytates (already mentioned in the iron section) that inhibit zinc absorption. Studies suggest that vegetarian diets have about 35% lower zinc absorption compared to omnivorous diets [5]. Some suggest that vegetarians may need to consume up to 50% more zinc than non-vegetarians [11].

Are your zinc levels optimal? If you notice your zinc levels decreasing over time, it may be time to make changes to your diet. You can increase your zinc levels by eating pumpkin seeds, nuts, and beans, or supplementing. Remember to always talk to your doctor before taking any supplements – they may interfere with your health condition or your treatment/medications!

3) Vitamin B12

Vitamin B12 is essential for brain health and making DNA and red blood cells. It is mainly found in animal products such as meat, eggs, and dairy. When their diet is low in eggs and dairy, vegetarians can become B12 deficient, while vegans have to rely on vitamin B12 supplements [12, 13].

Some amounts of vitamin B12 can be found in vegetables, algae, and mushrooms. Significant amounts have been reported in fermented vegetables, such as sauerkraut, natto, and tempeh. However, the amount of vitamin B12 in all of these foods is either negligible or highly variable. Neither of these foods can be considered a constant and sufficient vitamin B12 source. That is because the presence of vitamin B12 in these foods depends on bacteria that can but don’t have to be present in the soil or among the fermenting microbes [14].

The liver can store vitamin B12, so it can take years before low B12 consumption becomes full-on B12 deficiency [15]. During this time, your B12 levels may be in the normal range, but actually suboptimal for health.

You can monitor your vitamin B12 levels by doing a simple blood test. If you follow a plant-based diet or used to be plant-based for many years, you may want to tweak your diet to keep your B12 optimal.

4) Vitamin D

It’s best if you get your vitamin D from the sun. But many people don’t get enough sunlight, often due to climate or their jobs. That’s when diet becomes important.

Vitamin D is important for mood, immune function, and muscle strength [16, 17]. Although a form of vitamin D is found in plants (vitamin D2), some studies suggest it is not as potent as cholecalciferol (vitamin D3), the type of vitamin D found in fish and dairy products [18].

Vegetarians, and especially vegans who don’t get enough sun, are at risk of having low vitamin D levels [19].

To increase vitamin D in your diet, opt for mushrooms [20].

5) Calcium

Calcium is a controversial nutrient. It is found in many plants, but so are oxalates and phytates that prevent calcium absorption. Low calcium decreases bone density and can lead to osteoporosis. Some studies indicate that vegans and vegetarians may be at a greater risk of having low bone mineral density [19, 21, 22].

On the other hand, there are studies that show plant sources to be adequate, and in some cases even preferred to dairy sources of calcium [23, 24, 25].

You can check your blood calcium levels – but these are often tightly maintained within a narrow range by the parathyroid hormone and vitamin D. If blood levels drop, calcium is taken from bone tissue [26]. That’s why it may be prudent to occasionally also check your bone mineral density (z-score, t-score) as you get older.

6) Iodine

Iodine is necessary for proper thyroid function. Both excessively low and excessively high intakes can lead to thyroid dysfunction. What’s interesting is that vegans fall into either of these groups, depending on their dietary choices [11].

Iodine is more commonly found in animal products than plants. Plant iodine content will depend on the iodine content of the soil. In a small-scale study, 80% of vegans and 25% of vegetarians had low iodine compared to 9% of people on an omnivorous diet [27].

However, occasionally, vegans can also have abnormally high iodine levels [28]. These cases are due to excessive seaweed consumption and can result in high TSH (thyroid-stimulating hormone) levels [29, 30].

Goitrogens, compounds found in raw cruciferous vegetables such as cabbage and cauliflower, can interfere with iodine use and may negatively affect thyroid function if consumed in excessively large amounts [11].

The easiest way to check your iodine is to do a quick urine iodine test. Low iodine levels? Talk to your doctor. Iodized table salt will usually do the trick [11].

7) Omega-3 fatty acids: DHA and EPA

We’ve all heard of the many benefits of fish oil, which is rich in omega-3 fatty acids DHA and EPA. Studies have shown that it protects against heart disease and depression and is great for your brain function. It turns out that vegetarians have much lower DHA and EPA intakes, while in vegans the intake of omega-3s is close to zero [31, 32, 33]. This is because DHA and EPA are mainly found in fish and seafood, with small amounts present in dairy.

While there are many studies that prove the benefits of DHA and EPA, there are no studies showing that their lack has adverse effects on vegetarians and vegans. To supplement or not – that’s currently a question open to debate [34].

It’s easy enough to get your EPA and DHA levels tested – usually as a part of an omega-3 index or omega-3/omega-6 panel that will also give you an estimated risk of heart disease. However, as already mentioned, the effect of low EPA and DHA in plant-based eaters is unknown.

How can you increase EPA and DHA in your diet? Another omega-3 acid, ALA (alpha-linolenic acid) can be converted to EPA at ~8-20% efficiency and to DHA at 0.5 – 9% efficiency [11, 35, 36, 37]. ALA is found in foods such as flax seeds, walnuts, and chia seeds.

Recently, DHA and EPA supplements derived from microalgae became available – and they have been shown to effectively increase blood DHA and EPA levels [38].

8) Cholesterol

Vegetarians and vegans usually have lower cholesterol levels [39]. This is great in terms of heart disease risk.

However, cholesterol is needed to produce hormones such as pregnenolone, DHEA, testosterone, and estrogens. Pregnenolone, for example, is also known as a “neurosteroid,” because it helps with various brain functions (cognition, memory, mood, etc.) [40]. Some studies have linked lower cholesterol levels to depression and anxiety [41, 42, 43]. It’s debatable whether or not lower cholesterol leads to decreased testosterone levels [44, 45].

Low cholesterol and the associated negative effects are most often linked to malnourishment – and less to a specific type of diet [46]. If your cholesterol is on the low side, you can always boost your levels by eating more oils, avocados, nuts, and seeds [11].

9) Protein

Plant-based protein is less digestible than animal protein. Again, plants contain anti-nutrients such as phytic acid and trypsin inhibitors, which reduce protein absorption. That’s why vegetarians and vegans should consume more protein in total than meat-eaters [11].

BUN (Blood urea nitrogen) levels are a measure of the amount of protein in your diet.

10) Selenium

Vegetarian and vegan diets may be lower in selenium [47, 48, 49]. Plants take in selenium from the soil; thus, people around the world eat different amounts of selenium daily, depending on the concentration of the mineral in the surrounding areas [50, 51].

Selenium is important for proper immune and cognitive function. If your selenium is on the low side, increase selenium-rich foods such as Brazil nuts, oats, and shiitake and button mushrooms.

About the Author

Biljana Novkovic

Biljana Novkovic

Biljana received her PhD from Hokkaido University.
Before joining SelfHacked, she was a research scientist with extensive field and laboratory experience. She spent 4 years reviewing the scientific literature on supplements, lab tests and other areas of health sciences. She is passionate about releasing the most accurate science and health information available on topics, and she's meticulous when writing and reviewing articles to make sure the science is sound. She believes that SelfHacked has the best science that is also layperson-friendly on the web.


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