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A Daily Vitamin D Supplement Can Help Prevent Autoimmune Disease, Huge Study Shows


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

vitamin d

The doses are higher than you'll likely find in the supermarket though. Image Credit: VH-studio/

A daily vitamin D supplement could reduce the rate of autoimmune disease by 22 percent – at least in the over-50s, a new study published this week in the BMJ has shown

Vitamin D – technically a type of steroid – is created naturally in the body from exposure to the sun. Even though its job description is to regulate the levels of calcium and phosphate in the body, making it nominally a bones-and-teeth kinda vitamin, it’s long been suspected to have a beneficial effect on the immune system as well.


While researchers have long had reason to think vitamin D supplements could be used to treat or prevent autoimmune disease, a causal link between the two has never been established – until now.

“We know vitamin D does all kinds of wonderful things for the immune system in animal studies,” senior author Karen Costenbader told New Scientist. “But we have never proven before that giving vitamin D can prevent autoimmune disease.”

In a huge, long-term randomized and double-blind trial – pretty much the gold standard – researchers from Brigham and Women’s Hospital set out to investigate two potential supplements’ ability to prevent autoimmune disease: vitamin D, and omega 3 fatty acids. Nearly 26,000 participants, all above the age of 50, were recruited from across the US and randomly assigned one of four daily regimens: either one vitamin D and one placebo supplement, one omega 3 and one placebo supplement, one vitamin D and one omega 3 supplement, or two placebo supplements.

“The great thing about randomized trials is they really answer the question of causation,” Costenbader told New Scientist.


While the group taking only omega 3 supplements also saw a reduction in the five-year incidence of autoimmune disease, the effect was not as large as for either group assigned vitamin D supplements.

The effect was even more pronounced after the first two years, rising from 22 percent to 39 percent – an overall reduction of nearly two fifths.

“It is exciting to have these new and positive results for non-toxic vitamins and supplements preventing potentially highly morbid diseases,” Costenbader said in a statement.

“Now, when my patients, colleagues, or friends ask me which vitamins or supplements I’d recommend they take to reduce risk of autoimmune disease […] I suggest vitamin D 2000 IU a day and marine omega-3 fatty acids (fish oil), 1000 mg a day – the doses used in [this study].”


Originally, the study – called VITAL – intended to investigate whether vitamin D and omega 3 fatty acid supplements could reduce the risk for developing cancer, heart disease, and stroke in people without a history of the conditions.

Just before the project was launched, however, the team decided to run an extra study looking at the rates of autoimmune diseases – conditions like rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease, and psoriasis – in the study participants.

“Given the benefits of vitamin D and omega-3s for reducing inflammation, we were particularly interested in whether they could protect against autoimmune diseases,” co-author JoAnn Manson, director of the parent VITAL trial, said.

While the results are certainly encouraging, the researchers know there is still more work to do. The team hopes their study will encourage professional societies to update guidance on supplements – the doses in the trial are much higher than those commonly recommended by health bodies such as the USA’s Food and Nutrition Board or the UK’s NHS – and they also hope to extend the study to include a younger demographic.


“Autoimmune diseases are common in older adults and negatively affect health and life expectancy. Until now, we have had no proven way of preventing them, and now, for the first time, we do,” first author Jill Hahn said.

“It would be exciting if we could go on to verify the same preventive effects in younger individuals.”


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