Obesity has been linked to more than a dozen types of cancer.
Previous studies have suggested that excess body fat could increase the risk of fatal prostate disease. But until now, there has been little research examining the timing of weight gain over the life course, the aggressiveness of the disease or on the overall chance of prostate cancer.
Experts said that the findings showed the “terrible impact that weight gain in early adulthood can have on men in later life”, saying young men were being bombarded with junk food adverts that made a healthy lifestyle hard to achieve.
The study could not show why early weight gain had such an effect, but said obesity appears to affect growth hormones in young adulthood, which may raise the risk of deadly prostate cancer.
NHS figures show that among men aged between 25 and 34 in England, 61 per cent are overweight or obese – almost twice the 32 per cent figure for those aged 16 to 24.
The study tracked men for an average of 43 years. In all, 23,348 participants were diagnosed with prostate cancer, with an average age at diagnosis of 70 years, and 4,790 men died from prostate cancer.
Weight gain at any stage of life was associated with both the development of prostate cancer and its aggressiveness. Further analysis found the link was driven by weight gain between the ages of 17 and 30.