There have been question marks about taking supplements to prevent health problems ever since research into beta-carotene in the 1990s dropped a bombshell.
Back then beta-carotene, the red-orange pigment that colours plant foods like mango and carrots, was a rock star of the nutrient world, with studies suggesting that a beta-carotene-rich diet reduced lung cancer risk.
But research giving beta carotene to smokers in the form of supplements, not food, delivered a nasty shock - these supplements appeared to increase lung cancer risk, not reduce it.
There was another surprise last year when US researchers linked a high intake of fish oil from both fish and fish oil supplements to a higher risk of prostate cancer.
Until then fish oil had one of the shiniest haloes of any supplement on the shelf - along with evidence that it could help protect the heart and reduce inflammation in rheumatoid arthritis, it was considered generally safe.
"We know that many lifestyle factors associated with heart disease, including being overweight, also increase cancer risk - so it may be that the men with a high intake of fish oil also had risk factors like being overweight."
This study left many men wondering what to do with their fish oil capsules - keep taking them in the hope of a health benefit or toss them out? Complicating things even more was another smaller study reported last November suggesting that fish oil might help slow prostate cancer growth. So what's a man to do?
Both studies do more to raise questions about fish oil than provide any answers, says Dr David Winkle, President of the Urological Society of Australia and New Zealand.
"Neither study tells us whether fish oil supplements are good for us or not in respect to prostate cancer - they just demonstrate that we need more research," he says, adding that the study linking fish oil to more prostate cancer didn't prove fish oil caused the disease, just that the men in the study with the highest level of fatty acids from fish oil in their blood also had a higher risk of prostate cancer.
"The study underscores the importance of looking critically at whether you need to take supplements generally and also the value of talking to your doctor to help assess what the risks and benefits of taking any supplement, including fish oil, are. Most men who have prostate cancer don't die of that disease and they often have a higher risk of dying from heart disease rather than prostate cancer."
Meanwhile, Dr Garry Jennings Director of the Baker IDI Heart and Diabetes Research Institute has stopped taking fish oil capsules himself - not because of concerns about prostate cancer but because the current evidence shows little benefit for people with a low risk for heart disease.
"However for people with high levels of triglycerides (unhealthy blood fats), fish oil in both supplements and food can help bring these levels down. Fish oil also has a mild blood thinning effect, although not as potent as aspirin," he adds.
Like David Winkle, Jennings was surprised at the finding linking fish oil with cancer.
"Most work I've seen in this area suggests fish oil is generally protective against cancer. But it can be difficult to nail down the reason for associations in some studies. We know that many lifestyle factors associated with heart disease, including being overweight, also increase cancer risk - so it may be that the men with a high intake of fish oil also had risk factors like being overweight. I'm being very speculative but often this can be a reason for a surprising finding in a study.
"But where there is consistent evidence is that people who eat fish appear to be less at risk from heart disease and cancer than people who don't," he says.
As for lifestyle measures that might lower prostate cancer risk, the Urological Society recommends regular exercise and sticking to a healthy weight.
"Poor exercise habits and a poor diet can increase the risk of metabolic syndrome - a cluster of symptoms including obesity and pre-diabetes that can increase the risk of cancer generally," says Dr Winkle.
- Sydney Morning Herald
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