It has long been suspected that vitamin D could help reduce the risk of developing an autoimmune disease, and now we have evidence this is the case – at least for people over 50
26 January 2022
Vitamin D supplements really do prevent people developing an autoimmune disease, at least for those over 50, in a study providing the first evidence of a causal link between the two.
Previous studies on the effect of vitamin D on autoimmune conditions have looked at vitamin D levels in those with an autoimmune disease or in those who go on to develop one. Other studies have hinted at the supplement’s beneficial effects on the immune system.
“We know vitamin D does all kinds of wonderful things for the immune system in animal studies,” says Karen Costenbader at the Brigham and Women’s Hospital in Boston. “But we have never proven before that giving vitamin D can prevent autoimmune disease.”
Costenbader and her colleagues randomly split nearly 26,000 people in the US who were 50 or over into two groups, giving them either vitamin D supplements or a placebo.
“The great thing about randomised trials is they really answer the question of causation,” says Costenbader.
The team tracked the participants for around five years to measure the development of autoimmune conditions, including rheumatoid arthritis, autoimmune thyroid disease and psoriasis.
This revealed that a dose of 2000 international units (IU) of vitamin D per day reduced the development of autoimmune disease by 22 per cent, compared with the placebo. This is a larger dose than the standard 400 IU recommended by health organisations such as the UK’s Department of Health and Social Care.
It is unclear how vitamin D prevents autoimmune disease, but we know it is processed in the body to produce an active form that can alter the behaviour of immune cells.
“There are tonnes of potential mechanisms,” says Costenbader. “It could be that vitamin D helps the immune system to distinguish between self [normal body tissue] and non-self [such as disease-causing microbes], or that it helps to decrease inflammatory responses to self.”
Costenbader now advises her patients to take 2000 IU of vitamin D a day, if they are the right age and it is safe for them to do so. However, she doesn’t recommend this for everyone. “You should tell your doctor if you start a supplement,” she says. “There could be reasons you shouldn’t take them.”
The researchers are now extending the trial to see how long the benefits last and hope to start a new trial in younger people. “I’m very excited and really quite bowled over by these results,” says Costenbader.
Journal reference: British Medical Journal, DOI: 10.1136/bmj-2021-066452
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