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Body size and risk of MS in two cohorts of US women

From the Departments of Nutrition (K.L.M., A.A.) and Epidemiology (A.A.), Harvard School of Public Health, Boston; and Partners Multiple Sclerosis Center, Department of Neurology (T.C.), and Channing Laboratory, Department of Medicine (A.A.), Brigham and Women’s Hospital, Harvard Medical School, Boston, MA.

Address correspondence and reprint requests to Dr. Kassandra L. Munger, Harvard School of Public Health, Department of Nutrition, 655 Huntington Ave, Building 2, 3^rd floor, Rm 312, Boston, MA 02115 kgorham{at}hsph.harvard.edu

Objective: To examine whether obesity during childhood, adolescence, or adulthood is associated with an increased risk of multiple sclerosis (MS).

Methods: Women in the Nurses’ Health Study (n = 121,700) and Nurses’ Health Study II (n = 116,671) provided information on weight at age 18 and weight and height at baseline, from which body mass index was derived. Women also selected silhouettes representing their body size at ages 5, 10, and 20. Over the total 40 years of follow-up in both cohorts combined, we confirmed 593 cases of MS. Cox proportional hazards models, adjusting for age, latitude of residence, ethnicity, and cigarette smoking, were used to estimate the rate ratios and 95% confidence intervals (CI).

Results: Obesity at age 18 (body mass index 30 kg/m²) was associated with a greater than twofold increased risk of MS (multivariate relative risk_pooled = 2.25, 95% CI: 1.50-3.37, p trend <0.001). After adjusting for body size at age 20, having a large body size at ages 5 or 10 was not associated with risk of MS, whereas a large body size at age 20 was associated with a 96% increased risk of MS (95% CI: 1.33-2.89, p trend = 0.009). No significant association was found between adult body mass and MS risk.

Conclusions: Obese adolescents have an increased risk of developing multiple sclerosis (MS). Although the mechanisms of this association remain uncertain, this result suggests that prevention of adolescent obesity may contribute to reduced MS risk.

25(OH)D = 25-hydroxyvitamin D; BMI = body mass index; CI = confidence interval; MS = multiple sclerosis; NHS = Nurses’ Health Study; NHSII = Nurses’ Health Study II; RR = relative risk.

Supported by grant NS047467 from the National Institute of Neurological Diseases and Stroke.

Disclosure: Author disclosures are provided at the end of the article.

Received May 12, 2009. Accepted in final form July 27, 2009.