Lack of vitamin D may be a direct cause of multiple sclerosis (MS), a genetic study has found.

The discovery may have “important public health implications” since so many people have insufficient levels of the essential vitamin, say researchers.

It helps explain why rates of MS, a potentially disabling auto-immune disease that damages nerve fibres, are higher in high-latitude regions such as Northern Europe which have fewer sunny days.

Sunshine triggering a chemical reaction in the skin is the primary source of vitamin D.

Previous studies have suggested an association between lower vitamin D levels and a higher risk of MS. But now scientists have demonstrated a genetic correlation that points strongly to a causal link.

Scientists who scoured the DNA of 33,996 participants identified four single-letter variants in the genetic code that were closely associated with a vitamin D blood marker.

A comparison between thousands of MS sufferers and healthy individuals found that people whose genetic make-up was associated with a lack of vitamin D – meaning they had fewer of the biomarker variants – were at least twice as likely to have multiple sclerosis.

Writing in the online journal Public Library of Science Medicine, the authors, led by Brent Richards from McGill University in Canada, wrote: “The identification of vitamin D as a causal susceptibility factor for MS may have important public health implications, since vitamin D insufficiency is common, and vitamin D supplementation is both relatively safe and cost-effective.

Whether vitamin D sufficiency can delay or prevent multiple sclerosis onset merits further investigation

“The importance of these findings may be magnified in high-latitude countries, which have disproportionately higher rates of MS and also higher rates of vitamin D insufficiency.”

The research showed that every ‘standard deviation’ decrease in genetic variants linked to the vitamin D biomarker doubled the risk of MS.

Standard deviation is a statistical measurement of variation from an average.

The finding provided “strong evidence in support of a causal role of vitamin D in MS susceptibility”, said the scientists.

They added: “Whether vitamin D sufficiency can delay or prevent multiple sclerosis onset merits further investigation in long-term randomised controlled trials.”

Vitamin D generated by sunlight is converted in the body into the blood marker 25-hydroxyvitamin D (25OHD). This is then further converted into the ‘active’ form of the vitamin, calcitriol, which acts as a powerful hormone.

25OHD levels in the blood are considered the best indicator of a person’s clinical vitamin D status.

MS occurs when the immune system attacks the protective myelin sheath that surrounds nerve fibres and acts as an insulator.

Nerve signals are disrupted, leading to symptoms that can range from mild tingling sensations to full-blown paralysis. In rare cases that progress rapidly, the disease can be fatal.

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