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