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Vitamin D and omega-3 fatty acids reduce autoimmune disease incidence

2nd February 2022

Vitamin D and omega-3 fatty acids when taken for a period of 5 years have been found to reduce the incidence of new autoimmune disease

Vitamin D and omega-3 fatty acids taken by adults over a 5-year period led to a 22% reduction in the incidence of autoimmune disease compared to placebo. This was the conclusion of a randomised trial by researchers from the Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, USA.

An autoimmune disease develops due to an immune-mediated attack on the body’s own organs although the underlying pathology for most conditions remains uncertain. Moreover, an estimated 4% of the global population is affected by one of the 80 different autoimmune disease which include conditions such as type 1 diabetes, rheumatoid arthritis, lupus, Crohn’s disease and scleroderma. Although epidemiological evidence indicates a potential preventative role for vitamin D in autoimmune diseases, prospective data are lacking. In addition, a Danish cohort study found that each additional 30g intake of fatty fish containing omega-3 oils was associated with 49% reduction in the risk of rheumatoid arthritis.

However, little is known about the potential synergistic effect of vitamin D and omega-3 fatty acids on the development of an autoimmune disease and this was the purpose of the present study by the US team. They undertook a randomised, placebo-controlled trial, VITAL, which was designed to investigate whether taking daily supplements of vitamin D3 (2000 IU) or omega-3 fatty acids reduced the risk of developing cancer, heart disease, and stroke in people who do not have a prior history of these illnesses. However, for the present analysis, the team focused on the development of the autoimmune diseases such as rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease and psoriasis. For the trial, participants were randomised to vitamin D or matching placebo and omega-3 fatty acids or matched placebo and self-reported all incidence autoimmune diseases which were confirmed by a review of their medical records. The primary outcome of interest was the incidence of all autoimmune diseases.

Vitamin D and omega-3 fatty acids and autoimmune diseases

A total of 25,871 individuals with a mean age of 67.1 years (50.6% female) were enrolled and followed for a median of 5.3 years. In the vitamin D arm, 123 individuals and 155 in the placebo group had a confirmed autoimmune disease (hazard ratio, HR = 0.78, 95% CI 0.61 – 0.99, p = 0.05). In the separate omega-3 fatty acids arm, 130 compared with 148 in the placebo group developed an autoimmune disease although this difference was non-significant (HR = 0.85, 95% CI 0.67 – 1.08, p = 0.19).

Using a Cox model adjusted for age, sex and race, the authors found that among those randomised to both vitamin D and omega-3, the incidence of confirmed autoimmune disease was lower (HR = 0.69, 95% CI 0.49 – 0.96) compared with placebo.

They concluded that vitamin D supplements with or without omega-3 fatty acids reduced the development of autoimmune diseases.


Hahn J et al. Vitamin D and marine omega 3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial BMJ 2022