Renal cell cancer : the role of physical activity and body size
Abstract: The aim of this thesis was to explore how physical activity, obesity, weight change, and birth weight influence the risk of renal cell cancer. The relation between occupational physical activity and risk of renal cell cancer was studied in a cohort of Swedish men and women identified in the nationwide censuses in 1960 and 1970, and followed for the occurrence of cancer by linkages to the Swedish Cancer Registry 1971-1989 (Paper I). We identified 2,704 male and 587 female cases with the same level of occupational physical activity in 1960 and 1970 (n=674,025 men and 253,336 women). In multivariate models, men with long-term sedentary jobs had a 25% increased risk compared to men with physically demanding occupations. In contrast, we found no clear evidence of an association between occupational physical activity and renal cell cancer risk among women. The association between occupational and leisure time physical activity and renal cell cancer risk was further studied in a prospective cohort of 17,241 Swedish twins (Paper II). Exposure information was obtained through a mailed questionnaire. During follow-up from 1967 through 1997 we identified 102 renal cell cancer cases. We found no evidence of a significant association between either occupational or leisure time physical activity and risk of renal cell cancer in this cohort. To evaluate the existing evidence that obesity increases the risk of renal cell cancer among both men and women, we conducted a quantitative summary analysis of published studies (Paper III). Fourteen studies on each sex assessed obesity as body mass index (BMI, kg/m 2 ), or equivalent, and were included in our analysis. In contrast to previous qualitative reviews, our quantitative summary showed that increased BMI is equally strongly associated with renal cell cancer risk among both men and women. The risk increased by 7% per one unit of increase in BMI (1 kg/m2 , corresponding to about 3 kg body weight increase for a subject of average height). The relation between body size and renal cell cancer was evaluated in more detail in a population-based case-control study with 877 patients with newly diagnosed renal cell cancer and 1,508 control subjects, frequency-matched by age (Paper IV). Exposure information was obtained through a mailed questionnaire. General and abdominal obesity (measured as BMI and waist-to-hip ratio, respectively) were independently associated with increased risk of renal cell cancer among both men and women. Furthermore, tall height was associated with an increased risk among both sexes. Weight gain and repeated weight changes in adult life were associated with an increased risk, especially among those with a high BMI already at age 20. The relation between birth weight, a marker of fetal nutrition and growth, and renal cell cancer was evaluated in the case-control study described above (Paper V). A total of 648 cases and 900 control subjects reported their birth weight and were included in the analyses. An increased risk of renal cell cancer was suggested among men with a high (>3500 g ) birth weight, compared to men with a birth weight between 3000 and 3499 g. We found no clear association among men with a low (<3000 g) birth weight, or among women. Our study shows that conditions in utero, reflected by birth weight, might affect the risk of renal cell cancer in adulthood.
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