In the first study, Dr. Boukje A. C. van Dijk, from Maastricht University in the Netherlands, and colleagues analyzed data from the Netherlands Cohort Study on Diet and Cancer, covering more than 120,000 older men and women.

During 9 years of follow-up, a total of 275 confirmed cases of renal cell carcinoma (RCC) were identified, the researchers report in the American Journal of Epidemiology.

For each 1 point in BMI above normal at the start of the study, the risk of RCC rose by 7 percent in men and women. Also, if BMI increased since age 20, the risk of RCC was elevated.

Unexpectedly, in women, for each 5-cm increase in height above 160 cm there was a 23 percent increase in RCC risk, the team notes. This was not seen in men, and it runs counter to what has been seen in most other studies, the researchers add.

In the second study, published in the same journal, Dr. Anders Engeland from the Norwegian Institute of Public Health in Oslo and colleagues conducted a similar analysis involving two million men and women living in Norway. During follow-up between 1963 and 2001, a total of 6453 cases of RCC were recorded.

In a separate analysis of 227,000 adolescents, 154 cases of RCC were seen.

In both age groups, the risk of RCC increased as BMI rose. The risk of the malignancy also increased with height, but further analysis showed this finding was confined to smokers and former smokers. In contrast, the link between BMI and RCC risk was strongest in those who never smoked.

"An effort should be undertaken to elucidate possible underlying mechanisms between factors such as BMI, BMI gain in adulthood, physical activity, and energy intake and cancer risk, specifically RCC risk," van Dijk's team notes.