Background: The relationships between body mass index (BMI) during early and middle-late adulthood and incidence of prostate cancer (PCa) by subtype of the disease (localised, advanced) and fatal PCa is unclear.
Methods: A population-based cohort of 36,959 Swedish men aged 45-79 years was followed up from January 1998 through December 2008 for incidence of PCa (1530 localised and 554 advanced cases were diagnosed) and through December 2007 for PCa mortality (225 fatal cases).
Results: From a competing-risks analysis, incidence of localised PCa was observed to be inversely associated with BMI at baseline (middle-late adulthood; rate ratio (RR) for 35 kg m(-2) when compared with 22 kg m(-2) was 0.69 (95% CI 0.52-0.92)), but not at age 30. For fatal PCa, BMI at baseline was associated with a nonstatistically significant increased risk (RR for every five-unit increase: 1.12 (0.88-1.43)) and BMI at age 30 with a decreased risk (RR for every five-unit increase: 0.72 (0.51-1.01)).
Conclusion: Our results indicate an inverse association between obesity during middle-late, but not early adulthood, and localised PCa. They also suggest a dual association between BMI and fatal PCa--a decreased risk among men who were obese during early adulthood and an increased risk among those who were obese during middle-late adulthood.