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March 02, 2020

Fish oil supplements may not protect against cancer – as previously believed

They may slightly increase the risk of prostate cancer, studies find

Adult Health Supplements
Fish oil supplements don't protect against -- may even increase prostate cancer risk Steve Buissinne/Pixabay

Fish oil supplements, which contain omega-3 fatty acids, may not protect against cancer, as previously believed, according to a pair of studies from the University of East Anglia in the United Kingdom.

The fats found in foods like fish, nuts and leafy vegetables have long been touted for their health benefits. But they may not play a role in preventing cancer – as previously believed, according to two new studies. 

Those essential fats, formally known as omega-3 fatty acids, must be obtained through food sources or supplements. The human body does not produce them. 

Previous studies have found omega-3 fatty acids help prevent heart disease and stroke and may offer some protection against cancer and other medical conditions.

The latest studies – both systematic reviews – affirmed that omega-3 fatty acids provide some heart health benefits, but they also found that the fats do not protect against cancer. They may even slightly increase the risk of prostate cancer. 

Still, the studies – completed by researchers at the University of East Anglia in the United Kingdom – found the fats' benefits and risks to be relatively small. 

For every 1,000 people taking omega-3 supplements for about four years, three people will avoid dying from heart disease, researchers found. Six people will avoid suffering a heart attack or another coronary event and three people will be diagnosed with prostate cancer. 

"Our previous research has shown that long-chain omega-3 supplements, including fish oils, do not protect against conditions such as anxiety, depression, stroke, diabetes or death," said lead author Lee Hooper, of the University of East Anglia's medical school.

The data shows that "if we take omega-3 supplements for several years we may very slightly reduce our risk of heart disease, but balance this with very slightly increasing our risk of some cancers," he said. "The overall effects on our health are minimal."

As part of the reviews, researchers examined 86 clinical trials of adults with evidence on cardiovascular events or deaths and 47 trials involving adults who didn't have cancer, were at increased risk of developing cancer or previously had cancer. 

Since most of the trials focused on fish oil supplements, the health effects of oily fish, which are also an important source of selenium, iodine, vitamin D and calcium, remain unclear, Hooper said.

The research was funded by the World Health Organization, and published in the British Journal of Cancer and the Cochrane Database of Systematic Reviews.

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