Being obese at 18 years of age can double a woman's later risk for multiple sclerosis, according to an analysis of data from two large, longitudinal cohorts.
The finding that weight during adolescence but not childhood or adulthood is associated with a twofold increased risk for MS further supports a growing body of evidence that the teenage years are important in the etiology of the demyelinating disorder, reported Kassandra L. Munger, Sc.D., of Harvard School of Public Health, Boston, and her associates.
According to previous research, the mechanism of the association might hinge on the low levels of serum 25-hydroxyvitamin D, a marker of vitamin D status, in obese individuals. Vitamin D is an immunomodulator that has been found to reduce the incidence and progression of MS in animal studies when present in high levels. Current thinking holds that the relatively low levels in obese adolescents could be an important risk factor, according to Dr. Munger.
The Nurses' Health Study (NHS) began in 1976 and involved 121,700 female, married registered nurses aged 30-55 years and living in 1 of 11 states at the time of enrollment.
The Nurses' Health Study II (NSHII) involved 116,671 female, married registered nurses who enrolled in 1989 when they were between the ages of 25 and 42 years, and lived in 1 of 14 states. Participants completed questionnaires on their health behavior and medical information every 2 years.
The researchers identified 241 women diagnosed with MS between 1976 and June 2002 in the NHS cohort. Of these, 166 cases were defined as definite and 75 as probable in the assessment by the patients' neurologists. Among the NHSII cohort, 352 women were diagnosed with MS between 1989 and June 2003; of these, 278 cases were definite, 74 probable.
Obesity during adolescence and adulthood was assessed using body mass index. The baseline questionnaires in 1976 (NHS) and 1989 (NHSII) included current weight and height. A later questionnaire completed in 1980 for the NHS cohort and 1989 for the NHSII cohort included data on their weight at age 18. In 1988 (NHS) and 1989 (NHSII), childhood BMI was determined by having women select which of nine silhouettes ranging from very thin to extremely obese best represented their body size at ages 5, 10, and 20 years.
Women with a BMI of 30 kg/m
Women who reported having larger body silhouettes at age 20 also had a twofold greater risk for MS, compared with those who reported a thinner body.
The risk for MS was not affected by obesity in childhood or at the age at the time of enrollment in either study.
Women with MS weighed less than did unaffected women. The decrease in relative weight occurred after the diagnosis, a finding that is consistent with those of previous studies.
Dr. Munger reported receiving travel and speaker honoraria from the Consortium of Multiple Sclerosis Centers and speaker honoraria from the National Multiple Sclerosis Society. Her associates reported several disclosures.