It was long thought that vitamin D could reduce the incidence of autoimmune diseases such as rheumatoid arthritis, psoriasis and lupus in the population. There were hints but no hard evidence, until now.

In a new study, US investigators found that people who took a high dose of vitamin D, or vitamin D and omega-3 fatty acids, for five years had a “significantly lower rate” of autoimmune diseases than people who took a placebo.

This was a large, randomised, double-blind, placebo-controlled trial, the “gold standard” study design that proves causation, and not merely association.

If the results hold true to the real-world, the incidence of these diseases, among the older population at least, would be cut by 22 per cent.

Where popular brands of vitamin D supplements have a daily dose of 1000 IU, the trial participants were given 2000 IU daily.

‘Never proven before’

The corresponding author of the study is Dr Karen Costenbader, a rheumatologist at Brigham and Women’s Hospital, and Professor of Medicine, Harvard Medical School.

She told New Scientist magazine: “We know vitamin D does all kinds of wonderful things for the immune system in animal studies.

“But we have never proven before that giving vitamin D can prevent autoimmune disease.”

Results confirmed in older people

The study participants came from a well-represented range of racial and ethnic groups. All participants were over 50 (mean age 67), so the results can’t be automatically generalised to a younger population.

However, there are hints that young people might be protected from autoimmune diseases by more exposure to vitamin D in sunlight.

In December, The New Daily reported that children, teens and young adults who spend at least 30 minutes outdoors during the summer months – when the sun is at its most potent – have a lower risk of developing multiple sclerosis (MS) as children.

First author, Dr Jill Hahn, a postdoctoral fellow at the Brigham, told the Harvard Gazette:

“Autoimmune diseases are common in older adults and negatively affect health and life expectancy. 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.”

The study

About 26,000 people in the US were recruited. The participants were given either vitamin D supplements only, or vitamin D and marine-derived long-chain omega 3 fatty acids, or omega 3 on its own, or a placebo.

Being a double-blind trial, neither participants nor researchers knew who was getting what.

The participants were tracked for five years.

Over that time, they answered questions about new diagnoses of diseases, including rheumatoid arthritis, polymyalgia rheumatica (an inflammatory disorder that causes muscle pain and stiffness, especially in the shoulders and hips), autoimmune thyroid disease, psoriasis, and inflammatory bowel disease.

They also recorded any and all other new onset autoimmune diseases.

Physicians reviewed patients’ medical records to confirm these reported diagnoses.

The results, as reported in the British Medical Journal:

“Vitamin D supplementation for five years, with or without omega 3 fatty acids, reduced autoimmune disease by 22 per cent, while omega 3 fatty acid supplementation with or without vitamin D reduced the autoimmune disease rate by 15 per cent (not statistically significant).”

The trial is still in play because the researchers want to see how long the benefits last. They hope to start a new trial in younger people.