Image copyright SPL Image caption This brain scan shows characteristic MS damage in the brain (highlighted in green)

People genetically prone to low vitamin-D levels are at increased risk of multiple sclerosis, a large study suggests.

The findings, based on the DNA profiles of tens of thousands of people of European descent, add weight to the theory that the sunshine vitamin plays a role in MS.

Scientists are already testing whether giving people extra vitamin D might prevent or ease MS.

Experts say the jury is still out.

It is likely that environmental and genetic factors are involved in this disease of the nerves in the brain and spinal cord, they say.

And if you think you may not be getting sufficient vitamin D from sunlight or your diet, you should discuss this with your doctor. Taking too much vitamin D can also be dangerous.

Vitamin D

Is important for healthy bones

We make it in our skin when we are exposed to sunlight, but some of it comes from our diet

Good food sources include oily fish, eggs, fortified breakfast cereals and fortified fat spreads

Some people - the elderly, pregnant and breastfeeding women, babies, children under the age of five, and those who do not get much sun - may not get enough and need supplements

Research around the world already shows MS is more common in less sunny countries, further from the equator.

But it is not clear if this relationship is causal - other factors might be at play.

To better understand the association, investigators at McGill University in Canada compared the prevalence of MS in a large group of Europeans with and without a genetic predisposition to low vitamin D.

Image copyright Science Photo Library Image caption People can get extra vitamin D from their diet or supplements

This type of genetic variation is pretty random and so the assumption is that any link found should be trusted.

The findings, published in the journal PLoS Medicine, indicated people with lower blood levels of a marker of vitamin D, due to their genetic predisposition, were significantly more likely to have MS than individuals without these genes.

Dr Susan Kohlhaas, from the MS Society, said: "There are many unanswered questions around what causes MS, so this large scale study is an exciting step towards understanding more about the complex nature of the genetic and environmental factors that contribute to it.

"There are government guidelines around how much vitamin D people should take, and taking too much can lead to side-effects, so we'd encourage people to talk to their health professional if they're thinking of doing this.

"We'd also welcome more research into this area, as we know it's really important to people living with MS."

Immunologist Prof Danny Altmann, from Imperial College London, said: "Vitamin D is relatively cheap, safe and many of us would be all the healthier if we could achieve the serum levels that our ancient ancestors presumably acquired when roaming outdoors in temperate climates, unclothed and eating a diverse diet including oily fish.

"While it may be too much to expect therapeutic vitamin D to treat or reverse ongoing MS, this paper will add to the weight of argument for routine vitamin-D supplementation of foodstuffs as a broad, preventative, public health measure."

The government is currently debating whether to recommend that all people in the "not so sunny" UK consider taking extra vitamin D.