CHAPEL HILL, N.C. -- A high level of physical activity in the year before a diagnosis of breast cancer seems to bestow a benefit for overweight and obese women but not for those of normal weight, according to researchers here.
CHAPEL HILL, N.C., Sept. 11 -- A high level of physical activity in the year before a diagnosis of breast cancer seems to bestow a benefit for overweight and obese women but not for those of normal weight, according to researchers here.
The 30% increase in breast cancer survival among the overweight subset of patients contributed to a modest overall exercise-survival benefit for 1,264 patients followed for eight to 10 years, reported epidemiologist Page E. Abrahamson, Ph.D., of the University of North Carolina, and colleagues, in the Oct. 15 issue of Cancer.
Although overweight and obese women later benefited from regular exercise, there was no benefit for normal weight and underweight women. As a result, after adjusting for other factors such as stage at diagnosis and income, the overall exercise benefit, was 22% (hazard ratio 0.78 [95% confidence interval 0.56-1.08] versus 0.70 [95% CI0.49-0.99] for overweight and obese women and 1.08 among ideal weight or underweight women [95% CI, 0.77-1.52]).
The findings were based on a follow-up study of 1,264 women who where diagnosed with invasive breast cancer from 1990 through 1992. The median age of the women was 42 (range 20 to 54), and 75% of the sample were white.
The women lived in New Jersey or the metropolitan Atlanta area at the time of diagnosis.
The epidemiologists interviewed women within months of diagnosis to determine their frequency of moderate or vigorous activity at age 13, age 20 and during the 12 months prior to cancer diagnosis.
There was no apparent benefit for exercise at age 13 or age 20.
The authors assessed physical activity by assigning metabolic equivalent scores to various activities, for example a vigorous activity such as running was assigned 9 METS and a moderate activity such as walking was assigned 5 METS. The quartiles were assigned by totaling the METS.
Women in the highest quartile had totals ranging from 35.1 to 98 METS while those in the lowest quartile had scores that ranged from 1.6 to 3.4 METS.
The authors did not assess changes in physical activity over a lifetime and they point out that could be a limitation of their findings. Moreover, they said that early symptoms of breast cancer in the year before diagnosis could alter activity and postdiagnosis behavior at the time of the interview could have influenced responses, both of which could have biased the observed hazard ratios.
Another potential limitation was the decision by 14% of the eligible women to opt out of the study. "Bias may have been introduced into this study if the relation between physical activity and survival in the nonresponders differed from that of the women who chose to participate," they wrote.
The study's strengths are its long term follow-up and the diversity of a population-based sample.
The authors concluded that although the benefit was modest, the finding that exercise may contribute to survival is encouraging "because few modifiable risk lifestyle factors for improving prognosis have been identified."