Effect of Diet and Physical Activity on Breast Cancer Survival

Clinical researchers, epidemiologists, and, especially, breast cancer survivors are interested in whether lifestyle modifications can influence breast cancer outcomes. Results of multiple studies have suggested that certain changes — including optimizing body weight, improving diet (reducing red meat intake and increasing vegetable and fruit [VF] intake), increasing physical activity, ceasing smoking, and moderating alcohol intake — are associated with better quality of life and longer survival. Because both diet and physical activity modify circulating gonadal hormone levels, such lifestyle modifications are intuitively appealing, but few objective data support a survival benefit for these habits.

To test the hypothesis that lifestyle changes affect clinical outcomes, investigators initiated a prospective study of 1490 women (mean age, 50) with early-stage breast cancer (diagnosed and treated from 1991 through 2000). All patients had been assigned randomly to the control group in a dietary trial (Women’s Healthy Eating and Living study). At baseline, participants provided four 24-hour dietary recalls on random days during a 3-week interval. Plasma carotenoid concentrations were used to validate reported VF intake. Physical activity was assessed at baseline using a validated questionnaire that queried about frequency, duration, and speed of walking outside the home, as well as frequency and duration of participation in strenuous, moderate, or mild exercise. Average follow-up was 6.7 years after baseline data collection.

In univariate analyses, higher tumor stage and grade were associated strongly with earlier mortality. High VF intake, high physical activity, and body-mass index within the normal range were associated weakly with later mortality. In a multivariate Cox model that included baseline VF intake and physical activity, the combination of consuming five or more servings of VF daily plus activity equivalent to walking 30 minutes daily was associated with a significant relative reduction in mortality (hazard ratio, 0.56). This survival benefit was observed in both obese and nonobese women, although a smaller proportion of obese women than nonobese women were physically active. The survival benefit of high VF intake plus high physical activity was noted in patients with estrogen-receptor (ER)-positive breast cancers but not in those with ER-negative tumors.