Obese men appear to have an increased risk of being diagnosed with advanced prostate cancer and of dying from the disease. Few studies have examined the impact of weight gain during adulthood on prostate cancer risk and mortality and these have reported conflicting results. We analysed data from 20,991 Norwegian men who participated in two phases of the Nord-Trøndelag Health Study in 1984/1986 (HUNT-1, when aged at least 20 years) and 1995/1997 (HUNT-2). Weight and height were measured at both HUNT-1 and HUNT-2, allowing each man's change in weight and body mass index (BMI) to be computed. During a median of 9.3 years of follow-up after the end of HUNT-2, 649 (3%) men developed prostate cancer. We observed no increase in prostate cancer incidence amongst men who put on weight between HUNT-1 and HUNT-2. In multivariable models, including adjustment for weight at HUNT-2, the hazard ratio (HR) for prostate cancer per one standard deviation, SD (6.2 kg) gain in weight was 0.98 (95% confidence interval [95% CI]=0.87-1.10, p-trend=0.70) and per one SD gain in BMI (1.9 kg/m(2) ) was 0.99 (95% CI=0.90-1.10, p-trend=0.88). Amongst men diagnosed with prostate cancer (any stage), there was no evidence that gain in weight before diagnosis was positively associated with subsequent all-cause mortality (HR per one SD increase in weight=0.98; 95% CI=0.81-1.19, p-trend=0.86). We conclude that weight gain in adulthood had no effect on prostate cancer incidence or survival in this population.
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