Abstract
Prostate cancer (PCa) incidence has steadily increased in Sweden, more steeply in the mid-1990s caused by increased opportunistic prostate-specific antigen (PSA) testing. Tallness, normal weight, and non-smoking are associated with more PSA testing, which increases detection of low-risk and localised PCa. We investigated time trends of height, body mass index (BMI), and smoking with PCa risk in 171,889 men in Sweden aged 50-64 years at baseline, who were linked to nationwide cancer registers during follow-up. Cox regression determined the association of these factors assessed before 1980, 1980-1994, and 1995-2004 with PCa risk. During 15 follow-up years, 8,049 men were diagnosed with PCa. The association of height with PCa was weakly positive across all calendar periods. For obesity (BMI ≥30 kg/m(2)) vs. normal weight (BMI 18.5-24.9 kg/m(2)) and current vs. never smoking, the associations changed from null before 1980 (HR 1.03, 95% CI 0.86-1.23, and 1.11, 95% CI 0.97-1.27) to negative in 1995-2004 (HR 0.83, 95% CI 0.74-0.93, and 0.86, 95% CI 0.79-0.93; p(interaction) between periods = 0.05 and 0.001). In men with clinical characteristics available, height was positively associated with both aggressive and non-aggressive PCa whilst obesity and smoking showed negative associations only with non-aggressive PCa. These findings likely reflect differences in PSA testing by BMI and smoking habits and contribute important knowledge for etiological studies of PCa.