Taking omega-3 (fish oil) supplements does not protect against cancer, and may even slightly increase the risk of prostate cancer, according to a large systematic review published this past weekend in the British Journal of Cancer.
A second “sister” review published Sunday in the Cochrane Database of Systematic Reviews, found that omega-3 supplements may reduce the risk of coronary heart disease and related events (such as a heart attack), but that the benefit is marginal.
The Cochrane review updates an earlier version, published in 2018. It reported omega-3 supplements have little or no effect on reducing the risk of heart disease, stroke or premature death.
“These large systematic reviews included information from many thousands of people over long periods,” says Lee Hooper, the principal investigator for both of the new studies and an epidemiologist at Great Britain’s University of East Anglia, in a released statement. “This large amount of information has clarified 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.”
“The overall effects on our health are minimal,” she adds.
Popular but unproven
Health claims for omega-3 dietary supplements have been made for years, primarily based on the results of observational studies. Once the findings of randomized clinical trials (considered the gold standard of medical research) started coming in, however — and, particularly, once those findings were pooled into meta-analyses — the claims for omega-3 supplements began to look more and more dubious.
Other researchers have found the supplements do nothing to help ward off macular degeneration.
Yet, despite these compelling findings, people continue to spend their money on omega-3 supplements. And they are doing so in increasing numbers. The global market for omega-3 products — primarily dietary supplements, but also milk and other foods to which omega-3 has been added as a marketing tool by manufacturers — was estimated at $4.1 billion in 2019.
That figure is expected to reach $8.5 billion by 2025.
Many studies, many people
For the current review on omega-3 supplements and cancer, Hooper and her colleagues analyzed data from 45 clinical trials in which more than 100,000 people took part.
The participants included individuals who didn’t have cancer (although some were at high risk for the disease), as well as people with a previous cancer diagnosis.
For the review on omega-3 supplements and cardiovascular disease, the researchers examined 86 clinical trials, including three recent ones published in late 2018 and 2019.
The participants in these studies, who numbered more than 160,000, had varying risks of cardiovascular disease.
In all the studies reviewed, participants were randomly assigned to either an intervention group whose members increased their consumption of omega 3 (most often by taking a supplement) or to a placebo group of some kind.
Putting the numbers into perspective
Both reviews found that taking daily omega-3 supplements is unlikely to have any impact on an individual’s health.
“We found that there is no demonstrable value in people taking omega 3 oil supplements for the prevention or treatment of cancer,” says Hooper. “In fact, we found that they may very lightly increase cancer risk, particularly for prostate cancer.”
“This risk is offset by a small protective effect on cardiovascular disease,” she adds.
The key word is small, however. Very small.
To help put the reviews’ findings into perspective, Hooper and her colleagues offer this calculation: If 1,000 people took omega 3 supplements for around four years, three of them would avoid dying from heart disease, six would avoid a coronary event (such as a heart attack), one would avoid developing arrhythmia (heart irregularities) and three would develop prostate cancer.
For comparison, 30 people need to take a statin drug for 10 years to prevent one person from developing atherosclerosis (which is the primary cause of heart attacks, strokes and peripheral vascular disease), the researchers say.
“Long-chain omega-3 fats are much less effective than these drugs. … And almost all the people who take the supplements will not gain from them,” they write in a supplementary Q&A released with the reviews. (The benefits of taking statins to prevent cardiovascular disease among low-risk people is, however, a matter of controversy).
Eat food, not supplements
The two reviews were unable to determine if eating greater amounts of foods that contain naturally high levels of omega-3 fatty acids, such as nuts, seeds and oily fish (like salmon and tuna) has any effect on health.
“The evidence on omega 3 mostly comes from trials of fish oil supplements, so health effects of oily fish, a rich source of long-chain omega 3, are unclear,” Hooper points out.
“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,” she adds. “But we found that there is no demonstrable value in people taking omega 3 oil supplements for the prevention or treatment of cancer.”
Hooper also notes that the multi-billion-dollar omega-3 supplement industry is putting environmental strains on the world’s oceans.
“Considering the environmental concerns about industrial fishing and the impact it is having on fish stocks and plastic pollution in the oceans, it seems unhelpful to continue to take fish oil tablets that give little or no benefit,” she says.