Multiple sclerosis (also known as disseminated sclerosis) is an inflammatory and chronic disease that affects the central nervous system of the human body. It causes such symptoms as muscle weakness, coordination problems, fatigue, sensory problems, and overall general pain.

What the study basically states is that the further from the equator a person lives, the higher risk a person has of contracting multiple sclerosis. In other words, the less sunshine a person receives while a child, the more chance of getting MS later in life. The research team found that people from the Scandinavian countries, for example, had higher risk from MS than people who lived further south—nearer to the equator.

The theory, which has been stated for over fifty years, is informally called the “latitude hypothesis” or the “sunshine theory”.

The Mack team study is important in deciding if this theory is true or not because it has eliminated the variability of a person’s genes. Heredity plays a part in MS, but with the genetic side removed, the environment, specifically sunshine, also plays an important role.

The team accomplished the hurdle of removing genetics by searching databases for identical twins. They found 179 identical twins in which one adult had MS while the other one did not. Based on childhood exposure to the Sun—from an independent 1993 questionnaire given to the twins on exposure to sunshine—the twin that was exposed to less sunshine as a child was the one that in adulthood was more likely to have MS.

Statistically, the twin who was outdoors 25 to 57% more of the time than his/her twin sibling had lower risk of developing MS.

The study by the Mack team was written up in the July 24, 2007 issue of the journal Neurology. The article is titled “Childhood sun exposure influences risk of multiple sclerosis in monozygotic twins”. Mack’s fellow collaborators are Talat Islam, W. James Gauderman, and Wendy Cozen, all from the Department of Preventive Medicine at the University of Southern California (Los Angeles).

The study is a good step toward better understanding MS. It does not show, however, why small doses of sunshine seem to counter the negative affects of MS on a person’s muscular system. It also does not state why this association is not valid after adolescence. Further studies are recommended in order to understand these yet-to-be-known mysteries.


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