A study of multiple sclerosis (MS) rates in 30 countries worldwide suggested a link with lower exposure to sunlight, and thus with less production of vitamin D by the body. The scientists suspected that it was the ultraviolet B in sunlight which had a beneficial effect. It appeared central to the body's production of vitamin D. Sunlight has also been found to reduce blood pressure, helping to protect against heart disease and stroke.

The scientists nevertheless cautioned against overdoing sunbathing. The evidence that over-exposure to UVB increases the risk of skin cancer is currently stronger than the evidence of its beneficial properties.

This possible link is supported by a study into levels of oily fish in national diets (oily fish are rich in vitamin D). This found that countries like Norway and Japan, which have similar sunshine levels to the UK but where far more oily fish is eaten, have only half the UK incidence of MS.