Does vitamin D or fish oil affect the risk of autoimmune diseases?

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When you have an autoimmune disease, your immune system mistakenly attacks your own organs, tissues, and cells. Can vitamin D or fish oil help? The VITAL trial tested both.

In older people, rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease, and psoriasis are among the most common autoimmune disorders. (Type I diabetes, lupus, and multiple sclerosis typically strike at younger ages.)

Medications or other treatments can help manage them, but “there are no known effective therapies to reduce the incidence of autoimmune diseases,” says Karen Costenbader, a rheumatologist at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School.

So her study took advantage of the planned Vitamin D and Omega-3 Trial (VITAL) led by JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School. VITAL randomly assigned nearly 26,000 people in their 50s or older to take either vitamin D (2,000 IU), fish oil omega-3s (460 mg of EPA plus 380 mg of DHA), both, or two placebos every day for roughly five years.

Why test vitamin D and fish oil?

“Vitamin D is a hormone that goes into the nucleus of the cell and regulates a wide array of immune function genes,” explains Costenbader.

As for fish oil, “there’s evidence that omega-3 fats are anti-inflammatory, but no one had ever done a trial showing that taking a supplement would prevent or reduce the incidence of autoimmune disease.”

So every year of the VITAL trial, the researchers asked participants to report any new autoimmune diagnoses. They tried to confirm those reports with medical records.

The results

“After five years, we saw a 22 percent reduction in new cases of autoimmune disease in people taking vitamin D,” says Costenbader.

The omega-3 group did not have a significantly lower risk. However, when the researchers included not just confirmed cases, but also probable cases, they found an 18 percent lower risk of autoimmune disease in the omega-3 group. But those results need to be tested in a future trial.

“In particular, we had trouble confirming autoimmune thyroid disease because doctors don’t do a great job of pursuing whether a patient’s thyroid disease has an autoimmune cause,” explains Costenbader.

“Low thyroid levels in an older person usually have an autoimmune cause, but when doctors see a low or a high level of thyroid stimulating hormone, many just start treatment without confirming that the patient has autoantibodies.”

The researcher’s takeaway

“These are relatively rare diseases, so roughly 230 people would have to take vitamin D and fish oil for five years to prevent one new diagnosis,” says Costenbader.

“But I think it might be worth it, especially if you have a family history or are worried about autoimmune disease, because after rigorous testing in 25,000 adults for five years, we didn’t see any safety problems.”

However, adds Costenbader, “I’d say talk to your doctor before you start to take anything.” In some trials, large doses of vitamin D, especially when taken with calcium supplements, have increased the risk of kidney stones.

“And our results don’t apply to younger people,” she notes.

What about people with early symptoms of autoimmune disease?

“We don’t know the answer to that question,” says Costenbader. “It may be too late at that point.”

“But if people have early joint pains without a lot of swelling and some autoantibodies are elevated, I think these supplements may be worth taking.”