A new study has shown that vitamin D helps to control a gene that increases a person's risk of multiple sclerosis (MS).
Around 85,000 people in the UK have MS, which is the most common disabling neurological condition in young adults.
A number of previous studies have suggested a link between vitamin D deficiency and a higher risk of MS, but this is the first to provide evidence of why this might be.
The study, which is published in the journal PLoS Genetics, found that proteins which are activated by vitamin D switch a specific gene on, and that if too little vitamin D is available, the gene may not function properly, increasing the likelihood of MS.
Simon Gillespie, chief executive of the MS Society, commented: 'These remarkable results tie together leading theories about the environment, genes and MS, but they are only part of the jigsaw.
'Future experiments will help put the pieces together.'