Two recent large-scale studies found that increasing intake of omega-3 can slightly increase the risk of prostate cancer. A slight decrease in cardiovascular risk does however offset this impact.
Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs) commonly found in nature. One of these fatty acids, called alpha-linolenic acid (ALA), is an “essential fat” that is required for our bodies to function.
The human body can’t produce it though. The ingestion of omega-3s is also the best way to increase ALA levels in the body.
Omega-3 fatty acids are part of the cell membranes and play a role in the development of certain hormones, among other things.
For human health, three types of omega-3 have a role to play:
- ALA, which occurs in plant oils
- eicosapentaenoic acid (EPA), which commonly occurs in marine sources
- docosahexaenoic acid (DHA), which also occurs in marine sources
Because these fatty acids are found in a range of foods, the omega-3 deficiency among healthy adults in the United States is “virtually non-existent,” according to the National Institutes of Health (NIH).
Most people believe that omega-3, which is available as a supplement over the counter, can stave off a multitude of chronic conditions, such as cardiovascular disease and cancer.
There is a general assumption that raising the intake of PUFAs enhances wellbeing, but these assumptions are “scientifically uncertain” as the writers of one of the new reviews report. The writers set out to test some of these ideas.
Omega-3 and cancer
A number of studies have been looking over the years for links between omega-3 consumption and cancer. The results have thus far been inconsistent.
The authors conducted a analysis of existing research to give a clearer picture. We now have their findings published in the British Journal of Cancer.
The scientists have taken data from 47 randomized control trials which included 108,194 participants in all. They researched whether or not omega-3, omega-6 (another essential fatty acid), or total intake of PUFA may affect the risk of incidence of cancer, breast cancer, or prostate cancer.
Both the research studied included cancer-free adults and lasted for at least 1 year.
Overall, the authors conclude that increased intake of omega-3 or ALA has little or no impact on the risk of cancer growth. It may however very slightly increase the risk of prostate cancer.
They also found that that the total intake of PUFAs could marginally increase the risk of cancer diagnosis and death from cancer.
Omega-3 and heart disease
The other review, which appears in Cochrane Database of Systematic Reviews, examined results from 86 trials, including data from 162,796 people. As with the cancer review, each study was a randomized control trial and was running for at least 1 year.
The authors have analyzed the data, and conclude:
“Increasing EPA and DHA has little or no effect on deaths and cardiovascular events (high-certainty evidence) and probably makes little or no difference to cardiovascular death, stroke, or heart irregularities.”
“High confidence” in this context means the authors are relatively confident that the impact is not induced by conflicting variables or other factors.
Raising the intake of EPA and DHA, however, according to the authors, slightly reduced the “risk of coronary mortality and cardiac injuries.” That said, the authors note that these results may not translate into effect.
Eating more ALA does not appear to affect the risk of cardiovascular deaths, coronary deaths, or coronary events, but may reduce the risk of cardiovascular events and arrhythmia slightly.
Small effects
To put these results into perspective, the cancer study authors clarify that if 1,000 males increased their intake of omega-3, this will result in three additional prostate cancer cases.
Conversely, if 1,000 people upped their intake of omega-3, three would prevent death from coronary heart disease, six would avoid an incident of coronary heart disease, and one would avoid arrhythmias.
The findings, taken together, contradict the notion that the omega-3 is a cure-all. It has no effect on cardiovascular disease and cancer.
The cancer and cardiovascular reviews are part of a series of studies performed by the same research group.
Lead author Dr. Lee Hooper, of the Norwich Medical School of the University of East Anglia in the United Kingdom, describes some of their earlier findings:
“Our previous research has shown that long-chain omega-3 supplements, like fish oils, do not protect against conditions such as anxiety, depression, stroke, diabetes or death.”
It is worth noting that if a doctor has prescribed fish oil, before making any changes, it is best to discuss this with them.
“Given the environmental concerns about industrial fishing and the effect it has on fish stocks and plastic pollution in the oceans, it seems unhelpful to continue taking fish oil tablets that offer little or no value,” he concludes.