Physical Activity, Disability, and the Risk of Hospitalization for Breast Cancer Among Older Women

Background. A recent investigation of physical activity, disability, and the risk of breast cancer among older women in the Iowa 65 1 Rural Health Study reported a decreased risk of breast cancer among women with any disability compared with physically capable but inactive women (relative risk [RR] 5 0.4, 95% confidence interval [CI] 0.2‐0.9). Because of the intriguing nature of that association, those investigators urged replication before drawing any conclusions. Methods. We replicated the Iowa approach using the Longitudinal Study on Aging (LSOA), a nationally representative, prospective cohort study. The 3131 community-dwelling women for whom we had complete data for these analyses ranged in age from 70 to 98 years old at baseline in 1984. Using ICD9-CM 174 codes, linked Medicare hospital claims identified 77 women with hospitalizations for breast cancer between 1984 and 1991. Multivariable proportional hazards regression was used to model the risk for this event among disabled, inactive, moderately active, and highly active women. Results. No significant association between disability in older women and the risk of hospitalization for breast cancer relative to inactive older women was detected (adjusted hazard ratio [AHR]-0.78, 95% CI 0.41‐1.5). Highly active older women had a significantly reduced risk of hospitalization for breast cancer (AHR-0.42, 95% CI 0.19‐0.95). Conclusion. The intriguing finding from the Iowa 65 1 Rural Health Study that disabled older women’s risk for breast cancer was reduced could not be replicated in the LSOA, although power was limited. Highly active older women, however, had a significantly lower risk for breast cancer in both studies. AST year, a review of more than 20 studies on the association between physical activity and breast cancer yielded inconsistent conclusions and underscored the need for standardized methods for measuring physical activity in women (1). At the same time, this Journal published an intriguing finding from an investigation of physical activity, physical function, and the risk of breast cancer among women aged 65 years or older in the Iowa 65 1 Rural Health Study, one of the four sites of the Established Populations for Epidemiologic Studies of the Elderly (EPESE) (2). In addition to observing that higher levels of physical activity in older women were inversely associated with breast cancer risk, Cerhan and colleagues found a markedly decreased risk of breast cancer among older women with any disability compared with physically capable, but inactive older women (relative risk [RR] 5 0.4, 95% confidence interval [CI] 0.2‐0.9). Because the researchers had no clear reason for this protective effect exhibited in disabled older women, it was recognized that “this finding needs to be replicated before drawing any conclusions” (2). Accordingly, this brief report attempts to replicate that intriguing finding by using the Longitudinal Study on Aging (LSOA), a prospective cohort study that enrolled a nationally representative sample of community-dwelling persons ranging in age from 70 to 98 years old in 1984 (3). Medicare hospital claims were used to identify women with hospitalizations for breast cancer between 1984 and 1991, and vital status was taken from the National Death Index (NDI) for the same period. Although the Iowa EPESE and LSOA baseline interview items are not identical, they are sufficiently similar to facilitate a reevaluation of the association between physical activity, disability, and the risk of breast cancer hospitalizations among older women.