Harvard Study Links Teen Obesity in Girls to Increased Risk of Developing MS
A study of more than 200,000 female nurses suggests that those who were obese at the age of 18 were twice as likely to develop MS later in life. Obesity during earlier childhood or in adulthood was not associated with increased MS risk. Based on this study in women, it is not clear whether the same would hold true for teenaged boys. Kassandra L. Munger, ScD, Alberto Ascherio, MD, DrPH, and colleagues (Harvard School of Public Health, Boston) report their findings in Neurology (2009;73:1543-1550).
Background: While MS is not contagious or directly inherited, epidemiologists—the scientists who study patterns of disease—have identified factors in the distribution of MS around the world that may eventually help determine what causes the disease. These factors include gender, genetics, age, geography, and ethnic background. This study explores whether weight is a factor that affects MS risk.
The Study: The Harvard team collected information from women aged 25 to 42 who enrolled in the Nurses’ Health Study (a cohort of 121, 700 female registered nurses) and Nurses’ Health Study II (116,671 female nurses). During the course of the study, women reported their height and weight currently, and at age 18, and if there was a diagnosis of MS. Also, women selected a silhouette that described their body size at ages 5, 10, and 20. The investigators computed the body mass index (BMI), a measure of body fat based on height and weight. A BMI greater than or equal to 30 (kg/m2) is considered obese. Over the course of 40 years of follow-up, 444 cases of definite MS and 149 cases of probable MS developed among the nurses.
Women who had a BMI of more than 30 at age 18 were more than twice as likely to develop MS. Having a large body size (based on silhouettes) at age 5 or 10 was not associated with an increased MS risk, but a large body size at age 20 was associated with a 96% increase in MS risk. Adult BMI was not associated with increased MS risk.
Comment: Based on this study in women, it is not clear whether the same would hold true for teenaged boys. The authors comment that while a strength of this study is the large sample size, the reliance on “self-report” is a limitation. They hypothesize that if an association between teen obesity and MS is confirmed, a possible biologic mechanism might be the lower levels of vitamin D associated with obesity. Growing evidence indicates that vitamin D may help protect against the development of MS.
