Friday Jun 16 | BY |
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The accepted belief is that we get all the vitamin D we need from sunlight. But does the sun make enough? Vegetarians and vegans believe they get plenty of vitamin D from the sun and plants. Is that true?

Sunlight exposure triggers a two-step process that creates vitamin D3 (cholecalciferol), an essential vitamin for health. The second step in vitamin D synthesis is performed in the liver to produce 25(OH) D, a metabolite of cholecalciferol. 25(OH) D is the form of vitamin D measured in a blood test and is the best indicator of overall vitamin D status. Eventually, it makes its way to the kidneys where it becomes 1,25-dihydroxvitamin D (calcitriol). This form of vitamin D can also be measured in a blood test, but is mainly used to assess parathyroid status.

VItamin D

To get enough vitamin D from sunlight alone, you need 1,500 hours from late spring to fall when the sun is strongest. But, sunlight exposure alone does not provide adequate amounts of vitamin D3. Even in sun-drenched parts of the world, vitamin D levels are low when tested.

A 2012 study found that at least one-third of Australian adults were vitamin D deficient. Another study found that over 70% of Indian adults were low in vitamin D. A study of vegetarians in Pakistan found vitamin D levels low even in those from rural areas that had lots of sun exposure.

Since vitamin D from supplements and food is already metabolized, it is a more direct source than sunlight. So if most people, even in sunnier climates, don’t get enough vitamin D, do vegetarians fare better or worse?

Vegetarianism is increasingly popular in Western countries. Recent estimates suggest that at least 5% of the population consumes vegetarian diets, and this proportion is growing. Extreme forms of vegetarianism like raw food veganism are widespread in liberal urban centers like Austin, Miami, Santa Monica, and even New York City. Vegetarianism is regarded as a healthier lifestyle because vegetarians have a lower risk of chronic diseases than the general population. Vegetarianism is also considered more environmentally friendly.

Because of the increasing popularity of avoiding animal products, researchers are studying vegetarians around the globe to learn if they get enough vitamin D.

More than 50% of people worldwide don’t get enough vitamin D. Health experts acknowledge that vitamin D deficiency is a global concern, and may be a more significant concern for vegans and vegetarians.

Eastern Orthodox monks on Mount Athos in Greece eat simply plant-based diets and fast a lot of the time. Researchers found them healthy with optimal body mass index, nearly no cardiovascular disease, and no insulin resistance, but with profound vitamin D deficiency. Their average vitamin D level was about 8.8 ng/mL. That’s exceptionally low.

In a 2009 study of Seventh Day Adventist vegetarians, lower vitamin D intake was about 40% below recommended dietary allowance for vitamin D3. In the typical vegetarian diet, naturally occurring vitamin D is in trivial amounts. Vitamin D3 supplementation is recommended. But, according to the Adventist study, the RDA for vitamin D3 of 400 IU is inadequate to sufficiently raise vitamin D blood levels. The new recommendation is 1,000 IU daily. But is that enough for those eating a plant-based diet?

A 2012 study published in the European Journal of Clinical Nutrition reported that vegans had lower 25(OH) D than omnivores, but vitamin D status was also low among non-vegetarians.

It’s true that mushrooms and sea algae make vitamin D2 (ergocalciferol). Though vitamin D2 supplements are useful, a 2013 study found that taking a D3 supplement sustains 25(OH) D levels better than D2. It is also nearly twice as effective in raising low levels.

Among my vegetarian and vegan patients who don’t take supplements, 25(OH) D is usually below 30 ng/mL. The laboratory reference range is 30-100 ng/mL. Even those from sun-drenched places like Hawaii, Southern California, and South Florida have low vitamin D levels.

My clinical data agrees with the research studies: vegans tend to have the lowest vitamin D levels, but even non-vegetarians who don’t take vitamin D3 supplements still have levels below the desirable range. But, those who take vitamin D3 supplements or eat lots of cold water fish have healthier levels.

I’ve also measured vitamin D levels among Peruvian Andean indigenous people who spend most of their lives outdoors. Their vitamin D levels also tend to be low. A study of Ecuadorian Andeans found vitamin D insufficiency in more that 80% of children. Though not well understood, high altitude, even in tropical climates, doesn’t improve vitamin D status.

Risks for Vitamin D Deficiency:

  • Environmental conditions: latitude and altitude, pollution, cloud cover
  • Clothing style: headscarves, concealed clothing
  • Sunscreen
  • Breastfeeding: human milk is low in vitamin D
  • Dark skin complexion
  • Genetic variations
  • Age: older people have reduced ability to synthesize vitamin D
  • Chronic kidney or liver disease
  • Fat malabsorption
  • Inflammatory bowel disease like Crohn’s
  • Obesity: vitamin D is locked away in adipose tissue
  • Magnesium deficiency
  • Vegetarianism

Vegans are particularly susceptible to low vitamin D. Those who spend a lot of time indoors, live in cloudy regions, and who cover their body with clothing or sunscreen are most susceptible to vitamin D deficiency.

Because of the importance of vitamin D for health, I recommend everyone have a blood test to check Vitamin D, as 25(OH) D. That way you have a baseline.


I recommend at least two hours of daily sunlight exposure, consuming vitamin D dietary sources like fish and eggs at least twice weekly, and a vitamin D3 supplement daily. For vegetarians, I recommend a combination of sunlight and a vitamin D3 supplement.

It takes several months to improve your vitamin D status. Start with vitamin D3 2,000 IU daily. If you prefer vitamin D2, start with 2,400 IU daily. In three months, retest 25(OH) D. Aim for at least 55 ng/mL. Increase your vitamin D3 dosage as needed up to 5,000 IU daily. For my patients, I recommend a target of 70 ng/mL.

Vitamin D toxicity is rare. I lived a winter with the Siberian Yupik people in the Bering Sea. We ate large amounts of walrus and polar bear liver, and I never saw a case of vitamin D toxicity. However, some experience vitamin D hypersensitivity, which can raise the calcium level in your blood. If you suspect hypersensitivity, check you calcium and parathyroid hormone levels.

Dr. J. E. Williams


Dr. Williams is a pioneer in integrative and functional medicine, the author of six books, and a practicing clinician with over 100,000 patient visits. His areas of interest include longevity and viral immunity. Formerly from San Diego, he now resides in Sarasota, Florida and practices at the Florida Integrative Medical Center. He teaches at NOVA Southeastern University and Emperor’s College of Oriental Medicine.

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  1. Steve says:

    There is a special UVB sunlamp designed and made for the purpose of generating Vitamin D naturally in the body. The Vitamin D Lamp by SPERTI is tested, proven effective for generating vitamin d, and a session takes only five minutes. Convenient for those who cannot get outdoors into the sunshine, and especially for the darker winter months.

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