Taking daily supplements of vitamin D at 2,000 IU and 1,000 mg of omega-3 fatty acids resulted in a 22% reduced risk of developing a plethora of autoimmune diseases compared to taking a placebo, according to a National Institutes of Health-funded review of the large-scale VITAL study. Results were published in BMJ.

“Given the benefits of vitamin D and omega-3s for reducing inflammation, we were particularly interested in whether they could protect against autoimmune diseases,” JoAnn Manson, co-author and director of the parent VITAL trial at Brigham and Women’s Hospital, Harvard University, told the Harvard Gazette.

“Autoimmune diseases are common in older adults and negatively affect health and life expectancy,” Jill Hahn, first author and postdoctoral fellow at Brigham and Women’s Hospital, told the Gazette. “Until now, we have had no proven way of preventing them, and now, for the first time, we do. It would be exciting if we could go on to verify the same preventive effects in younger individuals.”

VITAL, a study which independently assessed high doses of vitamin D and omega-3 fatty acids and their associations with health outcomes, recruited 25,871 participants aged 55 and older and followed up with them for a median 5.3 years. The authors of the review followed medical records during the study duration, tracking for autoimmune diseases like rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease, and psoriasis.

For the vitamin D arm of the study, 123 participants in the treatment group and 155 in the placebo group had a confirmed autoimmune disease, representing a 22% reduction. In the omega-3 fatty acids arm, 130 participants in the treatment group and 148 in the placebo group had a confirmed autoimmune disease, the authors of the study said. While omega-3 fatty acid supplementation alone didn’t make a statistically significant difference, the rate was reduced by 18% among participants with probable autoimmune disease, pointing to an increased effect after longer duration of supplementation, the authors said.

“When only the last three years of the intervention were considered, the vitamin D group had 39% fewer participants with confirmed autoimmune disease than the placebo group, while the omega-3 fatty acid group had 10% fewer participants with confirmed autoimmune disease than the placebo group. In this two-by-two trial, supplementation with both vitamin D and omega-3 fatty acids decreased autoimmune disease by about 30% versus placebo alone,” the authors wrote.

Senior author Karen Costenblader, of the Brigham and Women’s Hospital’s division of rheumatology, inflammation, and immunity, told the Harvard Gazette that the team intends to determine if the effect of longer-term vitamin D supplementation results in a pronounced effect.

While the study was observational in nature, the authors proposed that a range of inflammatory-regulating activities exhibited by vitamin D, EPA, and DHA could in sum suppress certain inflammatory cytokines and chemokines, reduce antigen presentation capacity, increase the production of regulatory T cells (vitamin D), inhibit the production of C-reactive protein and inflammatory cytokines, decrease T cell proliferation and activation, and serve as substrate for specialized pro-resolving lipid mediators which promote the resolution of inflammation.

The authors of the study said that while the large and diverse sample of participants was strong, the results might not be generalizable to younger individuals who experience AD earlier in life. Additionally, the trial only tested one dose and one formulation of each supplement, and more follow-up is needed to determine whether the effects observed in this study could be long-lasting.