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Vitamin D and omega-3 fatty acids reduce development of autoimmune diseases

Vitamin D and omega-3 fatty acids when consumed over a 5-year have been found to reduce the incidence of new autoimmune diseases.

Vitamin D and omega-3 fatty acids consumption by adults for a period of at least 5 years, resulted in a 22% reduction in the incidence of new autoimmune diseases 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 because of an immune-mediated attack on the body’s own organs although the underlying pathology behind this process remains uncertain.

An estimated 4% of the global population is affected by one of the 80 different autoimmune diseases and which includes 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.

The role of fish in the development of autoimmune disease development is also not well defined though a Danish cohort study found that for each additional 30g intake of fatty fish containing omega-3 oils, there was an associated 49% reduction in the risk of rheumatoid arthritis.

However, whether there is a potential synergistic effect of vitamin D and omega-3 fatty acids on the development of an autoimmune disease is unknown and was the focus 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.

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