If there’s anything good to say about bowel cancer, it’s that there are some clues for prevention. Being physically active, not packing on the kilos and – maybe – a fibre rich diet can help reduce the risk. But for heading off prostate cancer, now the most commonly diagnosed cancer in Australian men, handing out useful advice isn’t easy.
Lifestyle is a suspect in the development of this disease and may partly explain why prostate cancer rates are higher in the US and Australia and lower in Asia, but nailing specific culprits is difficult, says Professor Graham Giles, Director of the Cancer Epidemiology Centre at the Cancer Council Victoria. Despite headlines linking more coffee and fewer dairy foods to a lower prostate cancer risk, the evidence is inconsistent.
This may be to do with the Jekyll and Hyde nature of the tumours that grow in the prostate.
“If they live long enough, most men will develop microscopic changes in their prostate that look like cancer,” says Giles. “Most of these tumours will be slow growing and unlikely to pose a real threat. Most men will die with this form of prostate cancer not from it. These tumours are like pussycats that just snooze away and don’t do any harm if you leave them alone, but a minority will be like tigers – they’ll be aggressive and they’ll spread. The problem is we’re not good at telling the two types of tumour apart and I think a lot of the uncertainty in research results is because we’re studying both slow growing and aggressive cancers together as if they are one disease.”
So far, obesity is one of the strongest preventable factors linked to aggressive prostate cancer – it may be one of the triggers that turns pussycats into tigers, says Giles who’s involved in a study of aggressive prostate cancer to learn more about the influence of lifestyle.
Smoking may play a part. It’s linked to increased mortality with aggressive prostate cancer - but we’re a long way off knowing for sure, he adds.
Interestingly, although diabetes can increase the risk of other types of cancer, it may be an advantage for prostate cancer - men with diabetes are less likely to be diagnosed with this cancer.
“Possible reasons are that high levels of insulin are thought to help cancer grow – and having diabetes long term results in lowered insulin levels,” says Giles. “Men with long term diabetes also tend to have lower testosterone levels which may also help protect against prostate cancer – but it’s speculative.”
Although some studies implicate a high consumption of dairy products, Giles says the evidence is still ‘soft’.
"There are so many dietary factors that come up but at this stage there’s no certainty. But a diet with more emphasis on vegetables and fruit, that includes fish, uses small amounts of meat and keeps your weight down isn’t going to do any harm," he says. "It’s healthy for the heart and may help protect against cancer generally. But there are no absolutes in this.
“With exercise the research gives mixed results – again this may be the effect of studying pussycats and tigers together. If we accept that obesity is part of the equation, then exercise may help ... and we know that most middle aged Australian men don’t exercise enough."
But there’s an argument for having more sex. A 2003 study by Giles linked more frequent ejaculation with a lower risk of prostate cancer, a finding backed up by other research.
"We don’t know why this is the case but there’s no harm in giving it a go," he says. "The prostate is there to produce seminal fluid and it’s there to be used," he says. "It may be like breast cancer. When breasts are used for their biological purpose – feeding babies – breast cancer risk is reduced."