People who spent more time in the sun as children may have a lower risk of developing multiple sclerosis, finds a small but intriguing study published in Neurology.
Researchers surveyed 79 pairs of identical twins who had the same genetic risk for MS yet in which only one twin had developed the disease.
The twins were asked to specify whether they or their twin spent more time outdoors during hot days, cold days, and summer, and which one spent more time suntanning, going to the beach and playing team sports as a child.
The study found the twin with MS spent less time in the sun as a child than the twin who did not have MS. Depending on the activity, the twin who spent more hours outdoors had a 25 to 57 per cent reduced risk of developing MS. For example, the risk of developing MS was 49 per cent lower for twins who spent more time suntanning than their siblings.
"Sun exposure appears to have a protective effect against MS," said study authors Talat Islam and Dr. Thomas Mack with the Keck School of Medicine of the University of Southern California in Los Angeles.
The study authors did not know the biological mechanism explaining the benefit of the sun but offered a couple of theories.
One is that exposure to ultraviolet rays may induce protection against MS by altering the cellular immune response. Or time in the sun may help the body produce more vitamin D, which may protect against the disease.
The study found the protective effect of sun exposure was seen only among female twin pairs, but Mack says this novel finding must be viewed with caution since only a few male twins were involved in the study.
Mack says high priority should be given to further research into how sun exposure reduces MS risk "if we are to unravel the mystery of what causes MS."
