Physical Activity and the Incidence of Multiple Sclerosis

Background: There is some evidence that exercise might modify disease progression in individuals with multiple sclerosis (MS), but little research has focused on whether physical activity is associated with the incidence of MS.

Objectives:  To study whether physical activity at multiple points in life is associated with a lower rate of incident MS in two large cohorts of women, the Nurses’ Health Study (NHS; n=121,701) and the Nurses’ Health Study II (NHSII; n=116,430).

Methods: Women reported information on recent physical activity in 1986 (NHS) and 1989 (NHSII) and on selected follow-up questionnaires. After excluding participants with missing or incomplete baseline physical activity information and those diagnosed with MS before baseline, there were 82,978 women in NHS (follow-up 1986–2004) and 116,002 women in NHSII (follow-up 1989–2009). Participants also reported early-life activity. There were 568 confirmed MS cases with MS diagnosis after baseline (117 in NHS, 451 in NHSII). To estimate relative rates (RRs) and 95% confidence intervals (CI), we used Cox proportional hazards models, adjusting for age, latitude of residence at age 15, ethnicity, cigarette smoking, supplemental vitamin D intake and body mass index at age 18. We carried out analyses separately in each cohort and then calculated pooled RR estimates.

Results: Women who reported 7–12 months per year of regular strenuous activity at ages 18–22 had a lower multivariable-adjusted rate of incident MS than those who reported no regular strenuous activity (RR_pooled = 0.75, 95% CI: 0.58, 0.98, p trend = 0.01). Physical activity at baseline was also inversely related to MS risk—compared with women in the lowest quintile of baseline physical activity, women in the highest quintile had a 30% reduced multivariable-adjusted rate of incident MS (RR_pooled = 0.70, 95% CI: 0.54, 0.90; p trend: 0.01).

Conclusions: These findings suggest that greater physical activity is associated with lower MS risk. However, we were unable to adjust for confounding due to UV light exposure, a major source of vitamin D, and cannot rule out the possibility that women reduce their physical activity in response to pre-clinical MS.