A woman’s risk of developing multiple sclerosis (MS) during her lifetime is doubled if she was obese at age 18, new research shows.

“This is the first study to link MS risk with obesity,” study co-author Dr. Kassandra L. Munger of the Harvard School of Public Health in Boston told Reuters Health in a telephone interview.

MS is a disease of the central nervous system. Up to half a million Americans have MS, with about 10,000 new cases diagnosed every year. While it is not usually fatal, it’s a chronic unpredictable disease with no known cure. The symptoms, including dizziness, blurred vision, slurred speech, sexual dysfunction, incontinence, shakiness, loss of coordination, and weakness, can be debilitating when flare-ups occur.

It’s not a common disease. According to Munger, women, generally, have a 1 in 200 risk of developing MS during their lifetime compared to the 1 in 8 lifetime risk of breast cancer.

Munger and her colleagues studied women enrolled in the Nurses’ Health Study and Nurses’ Health Study II over a 40 year period. Participants answered questions throughout the study about weight, height, body size, smoking and exercise habits, and disease status.

Among the more than 200,000 participants in the two groups, there were 593 cases of MS.

The study found no association between MS risk and having a large body size at ages 5 and 10 or as an adult. However, obesity at age 18 was associated with a greater than twofold increased risk of MS and a large body size at age 20 was associated with a 96% increased risk of MS, the study team found.

The findings, reported in the medical journal Neurology, underscore the obesity threat, Munger said. “We have another disease which being obese is associated with.”

The findings also provide another reason to encourage a healthy weight in young people.

“The prevention of adolescent obesity may contribute to reduced MS risk,” they conclude in their report.

The investigators caution that the study has its limitations. The findings need to be validated with further research and only apply to white women.

“There’s no reason to believe that the biological mechanisms would be different” in boys, Munger said, but the same can’t be said about the racial differences in the disease.

It’s possible that any genetic protection that may be at work for African Americans and Asians, who have a lower incidence of MS, may be “stronger than obesity would be at increasing their risk,” Munger said.

Weight is not the most significant risk factor for MS, Munger pointed out. The three top ranking risks are environmental: infection with the Epstein Barr virus, vitamin D deficiency, and cigarette smoking, she said.

SOURCE: Neurology, online November 12, 2009.