Plant-Based Diets, Micronutrients and Mental Health
Do vegetarian and vegan diets contain the micronutrients our brains need to function properly? Or do they put people at risk for serious deficiencies that increase the likelihood of developing psychiatric disorders?
In my last post, Food Fights: Are Vegan Diets Healthier for the Brain? we compared big-picture health effects of plant-based diets to meat-based diets, and discovered more similarities between them than many might have expected. Today, we go micro! We will explore each nutrient’s function in the brain, and the psychiatric symptoms that can develop if we don’t get enough of each one. I created this comprehensive summary of the science to be a resource for everyone, regardless of chosen diet, so that we may all improve our understanding of how to help our brains function at their absolute best.
You will notice that certain essential nutrients are missing. This is because those nutrients are generally easy to obtain from both plant-based and omnivorous diets. I also chose to reserve coverage of deficiency testing and supplementation for future posts, as complete discussion of any one of these fascinating nutrients would have been pages long (and believe me, I was going there…)
Before we get started, a few definitions:
- Vegan = completely avoids all animal foods, including dairy and eggs
- Vegetarian = avoids all animal foods except for dairy products and/or eggs
- Omnivore = eats plants and animals (may or may not eat eggs or dairy); pescatarians are included in this category
- Meat = the meat of any animal—red meat, poultry, seafood, etc.
- Animal foods = meat, eggs, dairy products
Ready? Onward!
Plant Micronutrients
Most people think of fruits and vegetables as teeming with the vitamins, minerals, and powerful antioxidants we need to live and thrive. It is true that many plant foods are rich in many of these substances, but just because a food contains a particular nutrient doesn’t mean we can access it. Unfortunately, plant nutrients often suffer from low “bioavailability”—which means that they are hard for us to extract, absorb, and utilize. Below I summarize the most important potential brain nutrient deficiencies that ALL plant-eaters—vegans, vegetarians and omnivores— need to be aware of, as well as key deficiency risks unique to vegans and vegetarians.
Fat-Soluble Vitamins (A, D, K2)
Vegan diets increase risk for certain fat-soluble vitamin deficiencies. Low-fat vegan diets further increase risk for these deficiencies, because sufficient fat must be eaten with every meal in order to absorb these vitamins from food.
Vitamin A
Contrary to popular belief, plant foods are lousy sources of vitamin A. In fact, they contain no vitamin A at all! Instead, they contain carotenoids, which we must then convert into retinol, the form of vitamin A our bodies can use. This is 12 to 24 times more difficult than obtaining retinol from animal foods. This helps to explain why childhood blindness due to vitamin A deficiency is rampant in dozens of developing countries, particularly in Africa and South-East Asia:
“Poor bioavailability plays a predominant role in the development of [Vitamin A deficiency] among communities that mainly rely on plant-based foods.” 1)
Fortunately, vitamin A deficiency in the U.S. and other developed countries is very rare, due to the abundance of animal foods and because many processed foods are fortified. Although vitamin A is important to many aspects of brain function including vision, learning, and memory, I’m not aware of any human studies demonstrating that vitamin A deficiency causes psychiatric disorders.
Vitamin D
The form of vitamin D our bodies need is vitamin D3 (cholecalciferol). We can make Vitamin D3 from sunshine or obtain it from animal foods.
The form of vitamin D found in plant foods is vitamin D2 (ergocalciferol). Our bodies can convert some D2 to D3, but D2 is less potent, doesn’t last as long in the bloodstream, and may be harder to store in our body fat for rainy days and dark winters.2) If we spend enough time in the sun, we don’t need to obtain any vitamin D from our diet at all, yet many people (regardless of chosen diet) are deficient. Most studies have found that vegans have lower blood levels of vitamin D3 and are more likely to drop to deficient levels during winter months than omnivores.3)
Vitamin D3 is important in brain growth and development, regulates calcium levels within the brain, helps protect brain cells from damaging oxidation, and supports the health of the hippocampus (the brain’s memory center). Lower levels of vitamin D3 are associated with an increased risk for schizophrenia, autism, depression, and dementia.4) But that doesn’t mean deficiency causes those conditions. Can D3 supplements help with psychiatric disorders? I did not find any clinical trials studying D3 supplementation and psychosis or dementia, and found only one study showing slight improvement in depression symptoms.5) However, several recent studies of Vitamin D3 supplementation have shown promising improvements in autism symptoms.6)
Vitamin K2
When most people think of vitamin K they think of vitamin K1, which is abundant in many plant foods, but vitamin K2 is just as important and often overlooked. Vitamin K2 is confusing because it comes in many forms, but the essential form we need is called MK-4, which only exists in animal foods. In the brain, MK-4 is required to build critical cell membrane components called sphingolipids, as well as to support the overall health and function of brain cells.7) It stands to reason that MK-4 deficiency could cause mental health problems, but I’m not aware of any human studies exploring the potential connection between K2 deficiency and any psychiatric disorder (K2 is poorly studied in general).
The body can convert a little bit of K1 into MK-4 (vitamin K2), but not nearly enough to fully meet our needs. Therefore, savvy vegans turn to natto (fermented soy), which contains a bacterial form of vitamin K that our bodies can turn into MK-4 a little more easily. For an excellent education on vitamin K, please see Chris Masterjohn PhD’s article The Ultimate Vitamin K2 Resource. He recommends that vegans take special supplements instead of relying solely on natto to meet their K2 requirements.
B Vitamins
Vitamin B12 (Cobalamin)
Vegan diets contain virtually no vitamin B12. Without this essential vitamin, the body cannot synthesize DNA, RNA, red blood cells, or myelin (the substance that wraps around and insulates our brain circuitry). Not surprisingly, B12 deficiency can CAUSE a whole host of serious psychiatric problems, including depression, psychosis, memory problems, mania, and changes in behavior or personality.8)
Severe, prolonged B12 deficiency is fatal. Most vegans and vegetarians are aware of this danger and either take supplements or consume fortified yeast (yeast doesn’t naturally contain any vitamin B12). Unfortunately, deficiency is still far more common than it should be, with some studies finding that as many as 86% of adults (regardless of chosen diet) are deficient. Researchers report wide ranges of values, but overall, vegetarians tend to have lower B12 levels than omnivores, and vegans on average tend to have the lowest B12 levels.9) Unfortunately, B12 blood levels often don’t always tell the whole story, so proper assessment requires additional tests, most commonly methylmalonic acid and total homocysteine levels.10) [More on the nuances of proper B12 testing and supplementation in a future post.]
Other B vitamins
Vitamin B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin) and B9 (folate) all work together to extract energy from food and build vital molecules. The brain is a high-energy organ, so even temporary, mild deficiencies of a single B vitamin can significantly disrupt normal brain function. All B vitamins are water-soluble, so what isn’t used is lost in the urine rather than stored in body fat. This means we need to eat good sources of B vitamins as often as several times per week in order to keep our brains functioning at their best.
All of the B vitamins except for B12 can be found in plant foods, yet some studies find that vegans are more likely to be deficient in vitamin B3 (niacin), B6 (pyridoxine).11), and B2 (riboflavin). Riboflavin seems to be the one that vegans need to pay the most attention to, as studies have more consistently shown higher risk of deficiency of this B vitamin in vegans compared to vegetarians and omnivores.
“Riboflavin deficiency is endemic in populations who exist on diets lacking dairy products and meat.”12)
All three of these B vitamins can be found in plant foods, but often in smaller amounts than animal foods, so it can be challenging to obtain adequate amounts from a vegan diet unless great care is taken to include just the right mixture of foods.
Riboflavin (Vitamin B2)
Riboflavin deficiency disrupts normal serotonin metabolism and brain energy production.13) Serotonin is a key neurotransmitter (brain communication chemical) that helps to regulate mood, appetite and sleep, among other things. Deficiency can cause fatigue, personality changes and general brain dysfunction.14)
Niacin (Vitamin B3)
Niacin is also required for proper serotonin metabolism and brain energy production. Severe niacin deficiency leads to pellagra, a disease which can cause depression, psychosis, delirium and dementia. Pellagra was common over a century ago in communities living on corn-based diets. Corn happens to contain a form of niacin our bodies can’t use, AND is low in tryptophan (the amino acid needed to form serotonin) resulting in a one-two punch to serotonin activity in the brain.15)
Pyridoxine (Vitamin B6)
Pyridoxine is essential for the synthesis of numerous neurotransmitters, including serotonin, dopamine, GABA, norepinephrine, and melatonin. The primary symptoms of vitamin B6 deficiency are depression, difficulty concentrating, and dementia.16)
Essential Minerals
Iodine
Most plant foods are quite low in iodine compared to many animal foods. Iodine is a required building block in thyroid hormone, which is critical in brain development and maintenance. Lack of iodine, particularly in early life, stunts body and brain growth. Iodine deficiency affects two BILLION people, and is the most common preventable cause of intellectual disabilities in the world.
Little is known about how simple iodine deficiency (without hypothyroidism) might affect brain function beyond infancy, although a recent Polish study found a correlation between lower iodine levels and certain symptoms of autism.17) Two randomized placebo-controlled clinical trials found that replenishing iodine to normal levels in schoolchildren improved their cognitive function.18)
Fortunately, iodine deficiency in the United States is uncommon due to the widespread use of iodized salt. Vegans, on average, have lower iodine levels than vegetarians, and are more likely to meet criteria for iodine deficiency on paper, but nevertheless appear to have normal thyroid function.19)
Iron
Many plant foods are lower in iron than animal foods, and to make matters worse, plants contain a form of iron that is far more difficult to absorb than heme iron, the form found in animal foods.20) Most vegans and vegetarians have about the same amount of iron in their blood as omnivores do, but their total body iron stores (how much they have in reserve) do tend to be lower.21)
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