Introduction: Few longitudinal studies have examined physical activity (PA) levels in breast cancer survivors and how those levels change following cancer diagnosis and treatment.
Methods: We conducted a longitudinal cohort study of 315 female residents of Washington State, aged 21-74 years, diagnosed with a first primary invasive breast cancer between 2002 and 2004, and identified by a population-based cancer registry. Recreational PA was assessed for the 2-year period before diagnosis and at three intervals after diagnosis (1-12, 13-18, and 19-30 months). We calculated average metabolic equivalent task (MET) hours/wk of total, low-, moderate-, and vigorous-intensity PA.
Results: Mean PA levels decreased by 50% in the 12 months after diagnosis relative to before diagnosis (from 18.8 to 9.2 MET-hours/wk). At 19-30 months post-diagnosis, overall PA levels had increased from the low levels reported in the first year after diagnosis, but remained approximately 3 MET-hours/wk lower than before diagnosis. Reductions were limited to moderate- and vigorous-intensity activities. Declines in PA differed according to certain characteristics of the study population, with the greatest reductions observed in women <40 years at diagnosis and with a pre-diagnosis body mass index <25 kg/m(2); these women were also more likely to report the greatest activity before diagnosis.
Conclusions: These results, if replicated in other studies, suggest that effective intervention strategies to increase PA in breast cancer survivors may differ according to patient characteristics.
Implications for cancer survivors: Younger, normal weight, and relatively active women may benefit most from interventions to minimize the decline in PA following diagnosis, while women who are older, overweight, and relatively inactive at diagnosis may benefit from interventions to increase long-term PA.