People who are genetically predisposed to have higher vitamin D levels may be less likely to develop psoriasis, an autoimmune condition where the skin develops inflamed and itchy patches. Until now, a similar link had only been seen between these gene variants and multiple sclerosis (MS), another autoimmune condition.
In many countries, people are advised to take vitamin D supplements, especially if they get little sun exposure, because the vitamin is made by skin cells in response to ultraviolet light.
But vitamin D has been the subject of many health claims that were later overturned. For instance, the belief that it can protect against and respiratory infections, including covid-19, has failed to be supported by randomised trials of supplements, the best kind of medical evidence.
Advertisement
鈥淰itamin D has been proposed to have effects on everything under the sun,鈥� says at the University of Cambridge.
Now, Burgess鈥檚 team has used a different kind of study to investigate vitamin D鈥檚 potential benefits. Called 鈥淢endelian randomisation鈥�, it uses random genetic variation in people鈥檚 natural vitamin D levels to stand in for the randomisation process used in trials of the supplements, for example if participants are randomly assigned to take vitamin D or a placebo.
There are at least four sites in our DNA where different genetic variants influence people鈥檚 natural vitamin D levels. The new analysis used genetic data on these variants and health records from more than 300,000 participants in UK Biobank, a large study that analysed people鈥檚 DNA and their health.
The team looked at whether the participants had ever been diagnosed with any of 28 autoimmune conditions, analysing these results for each condition.
Being genetically predisposed to having higher vitamin D levels was linked with a lower risk of psoriasis. The results also hinted that these variants protect against lupus, when the immune system attacks a range of tissues, including joints and the skin, but a statistical analysis suggests this finding may have arisen by chance.
Backing up a , Burgess and his colleagues also found that being genetically predisposed to having higher vitamin D levels is linked to a lower risk of MS, where the immune system attacks nerves and causes weakness and paralysis.
But the vitamin doesn鈥檛 seem to protect against other autoimmune conditions, such as rheumatoid arthritis. This may be because these different conditions are driven by different branches of the immune system, says team member at the University of Manchester, UK.
A previous randomised trial recently found that in people over 50, taking vitamin D supplements lowers the risk of developing a new autoimmune condition, but it wasn鈥檛 large enough to show whether the effect applied to all autoimmune conditions or just some of them. The latest study suggests the latter, says Zhao.
at McGill University in Montreal, Canada, says there should now be a randomised trial to see if vitamin D supplements can reduce the incidence of psoriasis. 鈥淲hen a Mendelian randomisation paper comes out with a positive result, you have to take it seriously.鈥�
MedRxiv
