The findings come from a study of 287,760 men aged between 50 and 71.
During five years of follow-up, 9,986 cases of prostate cancer and 173 deaths from the disease were noted.
Analysis showed that prostate cancer patients with a BMI of 35 or more had double the risk of mortality of men with a BMI below 25. Compared with normal weight, death risk was 46 per cent higher in those with a BMI of 30–34.9 and 25 per cent higher in men with a BMI of 25–29.9.
Incidence of prostate cancer was 33 per cent lower in men with a BMI over 40 than those with a BMI below 25. This may be because obesity makes the disease difficult to detect and a low uptake of prostate-specific antigen tests and digital rectal examination was noted among obese men in the study.
High BMI could be associated with a higher risk of death due to altered levels of circulating hormones, suggest researchers from the US National Institutes of Health. They said that depressed testosterone levels and increased levels of insulin-like growth factor and leptin in obese men could increase tumour progression.