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Vitamin D Supplement: Worthwhile or Worthless?

“Even the nation's top infectious disease doctor, Anthony Fauci, embraced the idea of using vitamin D to help keep COVID-19 at bay, saying in September [2021] that he takes a supplement to avoid being deficient and ‘would not mind recommending’ it to others.”

- Will Stone, health and science news reporter


“The great tragedy of science - the slaying of a beautiful hypothesis by an ugly fact.”

- Thomas Huxley, English biologist and educator



Between 1913 and 1948, scientists identified all 13 of the known vitamins. Once discovered, marketers actively promoted taking vitamins to supplement the allegedly deficient diets of Americans. By 1942 the appeal of vitamins to the American general public was described as “vitamania” even though there was little or no evidence that supplemental vitamins offered any benefits beyond that of eating a nutritional diet.

To this day, Americans seem to have an obsessive desire to supplement their diets with more vitamins. Yet, there still is no evidence that supplemental vitamins offer any benefits beyond that of eating a healthy diet. In this Germ Gems post, I focus on one vitamin, Vitamin D, and the results of recent research regarding whether taking a vitamin D supplement proved worthwhile.


Why we need vitamin D. Vitamin D has many biological effects including increasing intestinal absorption of calcium, magnesium and phosphate. Vitamin D is an essential vitamin that the human body uses for bone development and maintenance, but it also plays a role in the nervous, musculoskeletal, and immune systems of humans.


Vitamin D is a group of fat-soluble secosteroids, and for humans, Vitamin D2 and Vitamin D3 are the most important compounds in this group. Calcium is crucial for keeping bones healthy and Vitamin D3 stimulates the absorption of calcium from the gut. A deficiency of Vitamin D can cause rickets—a bone disease known since antiquity.


It’s called “the sunshine vitamin” for a reason. Most humans get their vitamin D from exposure to the sun, that is, cells in one’s skin can manufacture their own vitamin D when exposed to ultraviolet B (UVB) light from the sun giving rise to vitamin D3. This is the reason why vitamin D is dubbed the “sunshine vitamin,” and it explains why vitamin D deficiency is much higher in regions of the world where exposure to the sun is limited.

People can also get vitamin D2 and vitamin D 3 naturally from certain foods such as salmon, beef liver, and egg yolks. Since the 1930s some foods—milk, cereal, and some orange juices— have been fortified with vitamin D2 and D3. And, of course, there are vitamin D supplements.

Does vitamin D do anything for other organ systems? Over the past several decades, a plethora of observational studies suggested that vitamin D deficiency plays a role in cancer, cardiovascular diseases, diabetes, diseases of the immune system, and neuropsychiatric disorders. The results of two long-anticipated randomized placebo-controlled clinical trials cast serious doubt on this hypothesis.


One study named VITAL (Vitamin D and Omega-3 Trial) involved older adults (see the New England Journal of Medicine July 28, 2022 article, “VITAL Findings—A Decisive Verdict on Vitamin D Supplementation”). The second trial, carried out in children in Mongolia, is slated for publication in Journal American Medical Association Pediatrics. (See Dr. F. Perry Wilson’s Commentary in the November, 2022 Medscape, “The Surprising Failure of Vitamin D in Deficient Kids.”)


The conclusions of two experts who commented on the negative results of these clinical trials were similar. Jo-Ann Manson, M.D, Ph.D. and professor of medicine, Harvard Medical School and Brigham and Women’s Hospital, who was involved with VITAL, concluded that “Overall, it’s recommended that small to moderate amounts of vitamin D are adequate, and among the healthy population, most people do not need screening or supplements.” (See her October 12, 2022 Commentary in MedScape, “Vitamin D: Recent Findings and Implications for Clinical Practice.)


In his Commentary, Yale University Professor F. Perry Wilson suggests, “My basic gripe that you’ve got all these observational studies linking lower levels of vitamin D to everything from dementia to falls to cancer to COVID infection, and then you do a big randomized trial of supplementation and don’t see an effect. . . suggesting that your money is better spent on a day at the park rather than buying D3 from your local GNC.”


To help explain this conundrum, Dr. Perry proposes “that vitamin D is not necessarily the thing causing these bad outcomes; it’s a bystander—a canary in the coal mine. Your vitamin D level is a marker of your lifestyle; its higher in people who eat healthier foods, who exercise, and who spend more time out in the sun.”


Does vitamin D have immunomodulatory and antimicrobial activities? There’s no shortage of research-backed publications on the impact of vitamin D on the immune system and on its potential benefits in fighting infectious diseases. Of particular relevance to the ongoing COVID-19 pandemic, the results of most studies support the hypothesis that vitamin D attenuates the deleterious effects of the “cytokine storm” that is triggered by SARS-CoV-2. the cause of COVID-9.


Although some small clinical trials point to a therapeutic role of vitamin D in COVID-19, there are at least two randomized trials that left researchers “extremely disappointed.” (See the September, 2022 review in MedPage Today, “Vitamin D Failed to Stop COVID, Other Respiratory Infections.”)


In her review of the disappointing results of the VITAL trial, Dr. Manson points out that the results of a separate trial called “VIVID for COVID” will be published by the end of 2022. While she awaits the results of this trial, she advises that it’s reasonable to take 1000-2000 IUs of vitamin D daily, a dosage that’s known to be very safe.

What’s a person to do? Vitamin D insufficiency occurs in around 50% of the global population making it a global pandemic. Yet according to the recent studies referenced above, screening for a vitamin D deficiency or taking a supplemental vitamin D even at a low dose may be of little or no value.


I suggest, therefore, that you ask your personal doctor for advice before taking supplemental vitamin D. You may already have an underlying bone disorder calling for extra vitamin D, such as osteoporosis. But if not, skip the visit to your local vitamin store and instead concentrate on eating a healthy diet and exercising, especially out of doors where you can get “the sunshine vitamin” free of charge.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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