How can sun exposure reduce the risk of multiple sclerosis (MS)?

The British Medical Journal reported that children and adolescents who had high sun exposure had a decreased risk of multiple sclerosis (MS) later in life. "Sun exposure during childhood and early adolescence seemed to be most effective against MS, and higher sun exposure during winter months, when minimum ultraviolet (UV) radiation and vitamin D exposures occur, was particularly important," researchers wrote. Investigators at the University of Wisconsin -Madison saw similar results in an animal model of MS called experimental autoimmune encephalomyelitis (EAE).

Their studies showed that low-sunlight conditions can result in a higher risk of EAE in mice. These findings correlate with the reality that MS is almost nonexistent along the equator, while incidence rates increase as you move farther in each direction. More sunlight near the equator allows the body to produce more vitamin D, which scientists have hypothesized may account for the lower rates of MS there.

Just five to 30 minutes of casual sunlight exposure each day is enough to provide most people with the vitamin D they need, but 40 percent of people with MS may not get any sunlight exposure during an average week. Because clothing covering the skin and sunscreen can affect vitamin D absorption, the benefits of sun exposure have to be balanced with the risks. While some time in the sun may be helpful, burns or long-term exposure may be harmful to your health. UV radiation is believed to contribute to skin cancers, including melanoma.