Omega 3 is a type of fat. Small amounts are essential for good health and can be found in the food that we eat including nuts and seeds and fatty fish, such as salmon.
Increased consumption of omega 3 fats is widely promoted globally because of a common belief that it will protect against, or even reverse, diseases such as cancer, heart attacks, and stroke.
Currently, omega 3 fats are also readily available as over-the-counter supplements and they are widely bought and used.
But in two recent studies from the University of East Anglia, the researchers found that there is no strong value in people taking omega 3 oil supplements for the prevention or treatment of cancer.
Instead, the supplements may slightly increase cancer risk, particularly for prostate cancer.
The two studies are published in the British Journal of Cancer and the Cochrane Database of Systematic Reviews. The lead author is Dr. Lee Hooper.
In the studies, the team looked at 47 trials involving people who didn’t have cancer, who were at increased risk of cancer, or had a previous cancer diagnosis, and 86 trials with evidence on cardiovascular events or deaths.
More than 100,000 participants were randomized to consume more long-chain omega-3 fats (fish oils), or maintain their usual intake, for at least a year for each of the reviews.
The team examined the number of people who died, received a new diagnosis of cancer, heart attack, or stroke and/or died of any of the diseases.
They found that omega 3 supplements may slightly reduce coronary heart disease mortality and events, but slightly increase the risk of prostate cancer.
Both beneficial and harmful effects are small.
If 1,000 people took omega 3 supplements for around four years, three people would avoid dying from heart disease, six people would avoid a coronary event (such as a heart attack) and three extra people would develop prostate cancer.
The team’s previous research had shown that long-chain omega 3 supplements, including fish oils, do not protect against conditions such as anxiety, depression, stroke, diabetes, or death.
These large systematic reviews included information from many thousands of people over long periods.
This large amount of information has clarified that if people take omega 3 supplements for several years they may very slightly reduce their risk of heart disease, but balance this with very slightly increasing our risk of some cancers. The overall effects on health are minimal.
The team says evidence on omega 3 mostly comes from trials of fish oil supplements, so the health effects of oily fish, a rich source of long-chain omega 3, are unclear.
Oily fish is a very nutritious food as part of a balanced diet, rich in protein and energy as well as important micronutrients such as selenium, iodine, vitamin D, and calcium—it is much more than an omega 3 source.
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