LONG COVID: Harvard Study Finds That Vitamin D Supplements Decreased Risk Of Autoimmune Diseases


A new study by researchers from Harvard T.H. Chan School of Public Health, Brigham and Women’s Hospital, and Harvard Medical School have found that vitamin D supplements with or without Omega fatty acids decreased risk of autoimmune diseases.

The study involved a nationwide American randomized Vitamin D and omega 3 trial (VITAL), double blind, placebo-controlled trial with a two-by-two factorial design.

The trial involved a total of 25 871 participants, consisting of 12 786 men ≥50 years and 13 085 women ≥55 years at enrollment. The participants were followed for a median of 5.3 years. 18 046 self-identified as non-Hispanic white, 5106 as black, and 2152 as other racial and ethnic groups. The mean age was 67.1 years.


The study findings were published in the peer reviewed British Medical Journal. 


Autoimmune diseases, characterized by an inflammatory autoimmune response to self-tissues, are the third leading cause of morbidity in the industrialized world and a leading cause of mortality among women.12

Autoimmune diseases are chronic conditions with increasing prevalence with age and major societal and economic burdens due to a lack of effective treatments.34

Vitamin D and marine derived, long chain omega 3 fatty acids are two nutritional supplements investigated as potential autoimmune disease treatments. In vitro, the lipid soluble active form of vitamin D (1,25-hydroxyvitamin D) regulates genes involved in inflammation and acquired and innate immune responses.5

Animal models of autoimmune disease have reported vitamin D to be beneficial because it inhibits the development or progression of disease,5678 but observational studies have found conflicting results9101112; small trials of vitamin D supplementation in people with established autoimmune disease have mainly reported disappointing results.1314

Whether vitamin D supplementation can prevent autoimmune disease onset is still unknown and has not been tested in clinical trials. Randomized controlled trials of people with prevalent rheumatoid arthritis, systemic lupus erythematosus,15 and psoriasis16 have also shown improvements in outcomes with omega 3 fatty acids, but few studies have examined omega 3 fatty acids in autoimmune disease prevention.

A Danish observational study found a 49% reduction in rheumatoid arthritis risk for each 30 g increase in daily fatty fish intake (≥8 g fat/100 g fish).17 However, randomized controlled trials examining omega 3 fatty acid intake and autoimmune disease risk are lacking.

We report the effects of vitamin D and omega 3 fatty acid supplementation on autoimmune disease incidence (including rheumatoid arthritis, polymyalgia rheumatica, autoimmune thyroid disease, and psoriasis) within the large scale vitamin D and omega 3 trial (VITAL) over approximately five years of randomized follow-up.

We assessed whether the effects differed by age, sex, race, body mass index, and by baseline concentrations of vitamin D, or by eicosapentaenoic acid plus docosahexaenoic acid or dietary fish intake.

Clinical implications

This study of more than 25 000 older adults in the US provides evidence that daily supplementation with 2000 IU/day vitamin D or a combination of vitamin D and omega 3 fatty acids for five years reduces autoimmune disease incidence, with more pronounced effects found after two years of supplementation.

Autoimmune diseases are a group of heterogeneous conditions with similar underlying pathogenetic mechanisms and together are associated with considerable morbidity and mortality.

The clinical importance of these findings is high because these are well tolerated, non-toxic supplements, and other effective treatments to reduce the incidence of autoimmune diseases are lacking.

Additionally, we saw consistent results across autoimmune diseases and increasing effects with time. We are continuing to follow participants for two years in an extension study to test the time course of this autoimmune disease reduction effect. Further trials could test these interventions in younger populations, and those with high autoimmune disease risk.


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