Population attributable risk (PAR%) reflects the preventable fraction of disease. However, PAR% estimates of cancer have shown large variation across populations, methods, and data sources.
We evaluated variations in PAR% of postmenopausal breast cancer by obesity, alcohol, fruit and vegetable intake, and physical activity in the Nurses’ Health Study (NHS). For the low-risk method, the age-standardized incidence rate in the low-risk group was compared with the overall rate. The partial PAR% method estimated the PAR% by the risk factors while adjusting for other covariates. The conventional method estimated the PAR% based on the exposure distribution and relative risks in the NHS, or from US national surveys and meta-analyses. For each model, we compared the results obtained using baseline or repeated measurements.
When considering the risk factors simultaneously, within the NHS, the low-risk method yielded overall PAR% for the baseline, simple update, and cumulative average models of 17.4%, 25.2%, 29.3%; the partial PAR% method yielded estimates at 13.7%, 28.0%, 31.2%. When considering each risk factor individually and then combined, the estimates by the partial PAR% were 12.5%, 20.7%, 18.9%; while the conventional method gave corresponding PAR% of 13.8%, 21.1%, 18.6%. The estimated PAR% based on meta-analyses and US national surveys was 25.6%.
The three methods provided similar PAR% based on the same data source, timing of measurements, and target populations. However, sizable increases in the PAR% were observed for repeated measures over a single measure and for calculations based on achieving all recommendations jointly rather than individually.