Vitamin D supplements really reduce the risk of autoimmune disease

It’s long been suspected that vitamin D might help reduce the risk of developing an autoimmune disease, and now we have proof that it does – at least for people over 50.

Through Carissa Wong

Vitamin D supplements do prevent people from developing an autoimmune disease, at least for those over 50, in a study providing the first evidence of a causal link between the two.

Previous studies on the effect of vitamin D on autoimmune diseases have looked at vitamin D levels in people with an autoimmune disease or in those who develop one. Other studies have hinted at the beneficial effects of the supplement on the immune system.

“We know that vitamin D does all kinds of wonderful things for the immune system in animal studies,” says Karen Costenbader at Brigham and Women’s Hospital in Boston. “But we’ve never proven before that giving vitamin D can prevent autoimmune disease.”

Costenbader and his colleagues randomly divided nearly 26,000 people in the United States aged 50 or older into two groups, giving them either vitamin D supplements or a placebo.

“The great thing about randomized trials is that they really answer the question of causation,” Costenbader says.

The team followed the participants for about five years to measure the development of autoimmune diseases, including rheumatoid arthritisautoimmune thyroid disease and psoriasis.

This revealed that a dose of 2,000 international units (IU) of vitamin D per day reduced the development of autoimmune diseases by 22%, compared to placebo. This is a higher dose than the standard 400 IU recommended by health bodies such as the UK. Department of Health and Social Affairs.

It is not known how vitamin D prevents autoimmune diseases, but we do know that it is transformed in the body to produce an active form which can alter the behavior of immune cells.

“There are tons of potential mechanisms,” Costenbader says. “It could be that vitamin D helps the immune system to distinguish between itself [normal body tissue] and not self [such as disease-causing microbes]or that it helps to decrease inflammatory responses towards oneself.

Costenbader now advises his patients to take 2000 IU of vitamin D daily, if they are the right age and can do so safely. However, she does not recommend it to everyone. “You should let your doctor know if you’re starting a supplement,” she says. “There might be reasons why you shouldn’t take them.”

The researchers are now extending the trial to see how long the benefits last and hope to start a new trial in younger people. “I’m very excited and really overwhelmed by these results,” Costenbader said.

Journal reference: British medical journal, DOI: 10.1136/bmj-2021-066452

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