Body mass index, physical activity, and risk of renal cell carcinoma

Objective: To investigate the association between obesity and risk of renal cell carcinoma and to examine whether the association is modified by physical activity. Subjects: A population-based case-control study of 406 patients with renal cell carcinoma and 2434 controls conducted in Iowa. Methods: Information was collected on weight at the ages 20-29, 40-49, and 60-69 years, height, nonoccupational physical activity, diet, and other lifestyle factors. Renal cell carcinoma risk was estimated by odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for age, total energy intake, and other confounding factors. Results: Height and total energy intake were not associated with risk in either sex. In men, neither physical activity nor level of obesity in any period of life was significantly associated with risk. In women, lower physical activity was associated with higher risk (OR 2.5; 95% CI 1.2-5.2 comparing exercise < 1 time/month to > 1 time/day). Compared with women in the lowest quartile for BMI, the risks of renal cell carcinoma for women in the highest 10% of BMI in their 20s, 40s, and 60s were 1.4 (CI = 0.6-3.1), 1.9 (CI = 0.9-4.2), and 2.3 (CI = 0.9-6.0), respectively. When analyses were limited to self-respondent data, the corresponding ORs were 2.9 (CI = 1.2-7.4), 3.2 (CI = 1.3-7.5), and 2.1 (CI = 0.7-6.4), respectively. There was little evidence that physical activity modifies the association of BMI with renal cell carcinoma. Conclusion: Nonoccupational physical activity was inversely associated and obesity was positively associated with risk of renal cell carcinoma among women. The risk appeared to be greater for women in the highest 10% of BMI in their 40s. Our finding of little evidence of an interaction between physical activity and BMI requires confirmation.