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Winter Months Spent in Sunny Climates Can Lower MS Risk

July 2, 2018

Greater exposure to sunlight during the winter months — part of a person’s lifetime exposure to ultraviolet radiation — can help to lower the risk of multiple sclerosis (MS), a large U.S. cohort study suggests.

The study, “Lifetime exposure to ultraviolet radiation and the risk of multiple sclerosis in the US radiologic technologists cohort study,” was published in the Multiple Sclerosis Journal.

Increasing evidence suggests that poor exposure to ultraviolet radiation from sunlight, especially during childhood, is a potential risk factor for MS.

The mechanisms underlying this association are thought to be linked to the impact of the sun’s ultraviolet radiation on the immune system, or in the synthesis of vitamin D — whose deficiency is suggested to increase the risk of MS, although this connection was recently challenged.

“There is epidemiological evidence suggesting that low exposure to ambient UVR [ultraviolet radiation] during early life may be associated with MS and earlier symptom onset,” the researchers wrote.

A total of 39,801 participants also completed a series of questionnaires about places of residence and sun exposure — specifically, time spent outdoors on weekends and weekdays, history of sunburns and skin sensitivity to sunlight — and general health and lifestyle questions. The study also analyzed those with MS, including year of diagnosis.

Among participants, there were 569 self-reported MS cases, with medical records available for 203 of them. A review by MS-specialized neurologists confirmed an MS diagnosis in 148 cases.

The study population was predominately female (more than 90%), with a mean age of 44 at MS diagnosis. Results showed a trend for an increased risk of MS with lesser exposure to the sun’s ultraviolet radiation during winter months, but no effects were detected during summer months. The effects were consistent across groups younger than age 40.