Longevity Briefs: Does Taking Vitamin D Reduce Your Risk Of Autoimmune Disease?

Posted on 14 October 2022

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Vitamin D is a chemical compound that is synthesised when the skin is exposed to sunlight. Vitamin D is best known for its role in bone health, with vitamin D deficiency being associated with increased bone fragility. Vitamin D is also important for the immune system, generally suppressing inflammation and reducing the activation of the T and B cells, with the exception of a special type of T cell called a regulatory T cell (Treg). Tregs block the activation of rogue T cells that might attack the body’s own cells, an event that leads to autoimmune disease.

Scientists don’t understand exactly how autoimmune diseases are triggered, but higher levels of chronic inflammation seem to make them more likely. The effects of vitamin D on the immune system suggest that higher levels of vitamin D could reduce one’s risk of autoimmune disease, but few clinical trials have tried to study this possibility in humans.

What did the researchers do: In this paper, researchers looked at data from VITAL, a large clinical trial of vitamin D and omega 3 fatty acid supplementation. The trial had 25 871 participants in the US, aged 67 on average. Participants were randomised to receive either vitamin D (50 micrograms/day), 1 gram of fish oil per day (460mg eicosapentaenoic acid, 380mg docosahexaenoic acid), both of the above, or a placebo. They were asked to limit their vitamin D intake from other sources, and to avoid using other fish oil supplements. The trial was double blind, meaning neither the participants nor the people giving them the supplements knew who was in the placebo group. The participants were followed up for about 5 years.

Key takeaway(s) from this research: Vitamin D supplementation was associated with a 22% reduction in autoimmune disease by the end of the study when compared to placebo. Omega 3 fatty acid supplementation was associated with a 15% reduction in autoimmune disease, but this wasn’t a statistically significant effect. Taking both vitamin D and omega 3 fatty acids was associated with a 30% reduction in autoimmune disease. Most of this reduction occurred during the last three years of the trial.

Graph showing incidence of autoimmune disease for people taking vitamin D (blue line) and people taking the placebo (yellow line) over the course of 5 years.
Vitamin D and marine omega 3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial

The results of this study are quite encouraging for several reasons. Since this trial was randomised, double-blind and placebo-controlled, we can be confident that the vitamin D supplements caused the reduction in autoimmune disease frequency. There are over 80 different types of autoimmune disease that have a large collective impact on public health, but the researchers found vitamin D supplements to be consistent in preventing many conditions. Vitamin D also proved effective in people from a range of different ethnicities, though as participants were primarily older adults, we don’t know whether supplementation would be similarly effective in younger people.


Vitamin D and marine omega 3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial: https://doi.org/10.1136/bmj-2021-066452

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