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Today we’re going to talk about vitamins. Specifically, the two vitamins plant-based eaters might not be getting enough of — vitamin B₁₂ and vitamin D.

But how can we be low in any nutrients when we’re following the healthiest diet on earth?

Great question.

But before we get to the ‘essential’ answer, let’s examine our vitamin friends in a bit more detail.

What — Exactly — Is a Vitamin?

Polish biochemist Kazimierz Funk coined the term “vitamine” in 1912. The word is a combination of the words vital and amine and was later shortened in English to vitamin. (The first isolated substance had an “amine” group, but the “e” at the end was removed when it was shown that vitamins do not need to be nitrogen-containing amines.)

Vitamins are organic chemical compounds that can’t be synthesized by our bodies.  Since they must be obtained through our diet, they are considered essential.

Vitamins (and minerals) are called micronutrients, because they are required in much smaller amounts than other ‘essential’ nutrients, i.e. essential fatty acids or essential amino acids.

However vitamins differ from minerals in one significant way– minerals are durable inorganic compounds while vitamins are more fragile organic compounds–exposure to air along with cooking and/or storage can render them inactive.

The Perfect 13

There are 13 vitamins necessary for human health.

Four of these are fat soluble (A, D, E and K), which means they’re absorbed through the intestinal tract with a little help from our lipids or fats. The remaining 9 vitamins (8 B vitamins and C) are water soluble, which means they dissolve in water and are easily excreted by the body through urination.

Is something missing?

You might have noticed that the set of micronutrients we call vitamins skip over the letters F-J. There is an interesting reason for that; over the years those vitamins (F-J) were renamed, reclassified or discarded.

For example, essential fatty acids were initially called “Vitamin F”.  Over time, scientists became aware that essential fatty acids resembled fats and were not strictly micronutrients because we need them in much higher amounts.

You can easily get most of the vitamins your body needs (and in the amounts required for good health) by following a whole food, plant-based diet — except two: vitamin B₁₂ and vitamin D.  Let’s first focus on Vitamin B₁₂…

Why Vitamin B₁₂ Matters

Your body needs vitamin B₁₂ to perform a wide range of critical roles including normal functioning of the brain and nervous system, DNA synthesis, fatty acid and amino acid metabolism, and proper red blood cell formation.

Vitamin B₁₂ deficiency therefore may lead to anemia or potentially cause serious and permanent damage to the brain and nervous system.  A mild deficiency may be asymptomatic; poor memory, fatigue and depression may be experienced when B₁₂ levels are low.

Homocysteine is a non-protein amino acid that can be converted into cysteine or methionine through a reaction facilitated by vitamin B₁₂.  When B₁₂ levels are low, homocysteine starts to build up in the blood increasing the risk of endothelial cell injury, which in turn may lead to inflammation and atherosclerosis.  So lower vitamin B₁₂ and higher homocysteine levels may actually “attenuate” the benefits of a whole food, plant-based diet on cardiovascular health and become a possible risk for coronary artery disease.

Indeed, studies reveal that plant-based eaters that do not supplement their diet with vitamin B₁₂ seem to have higher levels of homocysteine and similar levels of carotid atherosclerosis than omnivores. However, B₁₂ supplementation in vegetarians with suboptimal vitamin B₁₂ status has been shown to significantly enhance arterial endothelial function.

Even though a plant-based lifestyle seems to be the best diet around, it is nevertheless naturally low in vitamin B₁₂.   In fact, a recent study of vegans in the UK revealed that over 50% of them presented vitamin B₁₂ deficiency!

Why so many of us may be low or deficient of this essential vitamin?

The answer is actually quite simple.

Vitamin B₁₂ must be obtained directly or indirectly from bacteria.

Before the days when we washed and scrubbed our vegetables until they are squeaky clean, it was easier to get B₁₂ from ‘dirty’ plant foods.

While today’s food hygiene practices do help us prevent a myriad of food-borne illnesses, they also explain why we have low intake of the essential vitamin B₁₂.

[Side note: herbivorous animals (e.g. cows) obtain B₁₂ from bacteria in their rumens (one of the chambers in their four-compartment ‘stomach’).  Animal-based foods indirectly provide B₁₂ because of those bacteria.]

So What Is the Best Way to Get Your Vitamin B₁₂?

There is a heated debate about whether you should source your vitamin B₁₂ through supplements or fortified foods.

I prefer supplementation for one simple reason. If you take a supplement, you can choose to take the bioactive form of B₁₂, in the amounts you need, and be certain you’re getting enough of it.

You can get B₁₂ through certain fortified foods, but it’s important to note that they usually contain a semi-synthetic form (cyanocobalamin) of the vitamin, which is converted by the body into the active form (methylcobalamin).

Fortified foods use cyanocobalamin because it is more stable and allows for longer shelf life. The problem however is that most fortified foods (like nutritional yeast or plant-based milks) are used for cooking which in effect may inactivate B₁₂.  Fortified foods should also be eaten daily, and preferably more than once a day.  In the end, you might not be getting what you think you’re getting. If you’re getting any B₁₂ at all.

How Much B₁₂ Does a Plant-Based Eater Need?

So if so many of us may be low in vitamin B₁₂ and supplements are an easy solution, the next question is how much do we actually need?

The good news is only tiny amounts are needed because the human body does a great job of recycling and storing B₁₂.

The current recommendation is about 4-7 micrograms (mcg) per day as a liquid, chewable or sublingual supplement. However it is important to note that you actually need to take more than 4-7 mcg in order to absorb that much into your body.

Here are two alternative ways to ensure you are getting the vitamin B12 that you need:

  • Daily: if you take a daily supplement, take at least 250 mcg per day.
  • Weekly: or you can take 2,500 mcg every week, which is the simplest method for most people.

It’s important to note that since B₁₂ is water soluble, it does you no good to take more than the recommended dosage. Your body will eliminate the excess through urination. Don’t overdo it then–you’ll simply be wasting money!

What About Vitamin D?

Let’s now turn to a second essential vitamin–Vitamin D.

Vitamin D enhances the intestinal absorption of minerals like calcium, magnesium, iron and zinc, and its bioactive form, calcitriol regulates the concentration of calcium and phosphate in the blood and the remodeling of bone.

Though some foods may contain vitamin D, 80% to 90% of our vitamin D is produced in the skin through sun exposure, i.e. UVB radiation. That is why vitamin D has long been called the “sunshine vitamin”.

The problem? For starters, given the current sedentary indoors lifestyles (or desk jobs), most of us can’t get enough of it like that.

Secondly, what’s the best way to prescribe how much sun any individual might need?   It depends on a lot of variables, including the latitude where you live, your age, your skin color, how much skin you expose, what time of day, what time of year, whether or not you use sunscreen…and on and on. That’s why it’s not easy to make a sun exposure recommendation that fits everyone.

And, it’s not fail-safe, either. Low vitamin D levels have even been recorded in young skateboarders in Honolulu who are mostly Caucasian and run around half-naked in the sun for about 30 hours every week.

Among plant foods, only mushrooms have been shown to contain small levels of vitamin D; but for mushrooms to produce vitamin D, they also need to be exposed to ultraviolet light. That means most mushrooms bought at the grocery store won’t have any vitamin D because they are grown in the dark.

So Do We Need Vitamin D Supplements?

It depends.

Ideally, we would get enough vitamin D from sunlight exposure (or food intake). But that may not always be possible, especially during the winter months and at higher latitudes.  If we do choose to take supplements, two questions remain–how much do we need and which Vitamin D (D₃ or D₂) should we take?

How much vitamin D do we need is a crucial question. Unlike B₁₂, which you can start taking without much worry, too much vitamin D may be harmful to your health. That’s why you should get your D levels checked by a doctor to find out if you need supplementation.

Having said that, the current recommendation from the National Academy of Medicine (formerly the Institute of Medicine) is that you take about 600 IU of Vitamin D a day. Their recommendation is based on bone health and it prescribes the amount necessary to bring serum levels to 20 ng/mL. This dietary reference intake (DRI) presumes a combined total intake from food and supplements.

Vitamin D exists in several forms, and the two most important ones are vitamin D₃ or cholecalciferol and vitamin D₂ or ergocalciferol. Ergocalciferol is the main form derived from irradiated mushrooms, while cholecalciferol is the natural form of vitamin D made by your body from exposure to sunlight. For that reason, many health professionals believe D₃ to be the best form for supplementation.

Nonetheless, a randomized, placebo-controlled, double-blinded study of healthy adults showed that identical daily doses of vitamin D₂ or D₃ (or a combination of D₂ and D₃) seem to be equally effective in increasing serum levels and maintaining vitamin D status.

A recent systematic review and meta-analysis reached similar conclusion. Daily supplementation of up to 4,000 IU of either D₂ or D₃ is similarly effective in raising serum levels of vitamin D. However, the study also showed that, when vitamin D is supplemented weekly or monthly, in doses up to 50,000 IU, D₃ seems to work better.

In a Nutshell

Vitamins B₁₂ and D are critical to brain, heart, and bone health.

Because they are not naturally found in plant foods, supplementation may be recommended or even necessary (in the case of B₁₂).

Choose a B₁₂ supplementation plan you can follow and have your vitamin D levels checked by your doctor for a long, healthy, plant-based life.

Rosane Oliveira, DVM, PhD

President & CEO, Plant-Based Life Foundation | Dr. Rosane Oliveira combines a lifelong passion for nutrition with 25 years of genetics research to create programs that help people develop healthy habits on their journey towards a more plant-based lifestyle. She is a Visiting Clinical Professor in Public Health Sciences and was the founding director of the first Integrative Medicine program at the UC Davis School of Medicine. She completed her postgraduate studies in Brazil and did her postdoctoral training in immunogenetics and functional genomics at the University of Illinois at Urbana-Champaign.