Of all the supplements that people take, most have been shown to be either useless, or even harmful once they are studied in well-run clinical trials.
But, one of the most popular supplements, omega-3 fish oil, has generally been regarded as safe and beneficial to health. But an observational study published this week in the Journal of the National Cancer Institute raises some potentially alarming concerns about consuming large amounts of the supplement.
Researchers at the world renowned Fred Hutchinson Cancer Research Center in Seattle found that men who took the supplement were 71 percent more likely to develop high-grade (the most dangerous form) prostate cancer, and 44 percent more likely to develop all forms of the disease.
The team, led by Dr Alan Kristal concluded: There is really no evidence that taking dietary supplements is beneficial to health, and there is increasing evidence that taking high doses is harmful.
This is hardly the first strike against fish oil. Indeed, a 2012 paper in JAMA reviewed 20 studies involving the effectiveness of omega-3 supplements in preventing heart disease, and found that there was no benefit in reducing strokes or heart attacks.
Taken together, all of this sounds quite damning. However, as ACSH friend Dr. David Seres, director of medical nutrition at Columbia University Medical Center cautions, This kind of study a rehashing of data obtained from another study in which the variable in the current study was not either part of the original design nor part of a randomized intervention is only valid for raising questions. Regardless of whether the subjects were chosen at random, the amount of fish oil consumed was not randomized.
He adds, So, you cannot say anything about whether the intake of fish oil had anything to do with the development of prostate cancer, just that higher levels in the blood were associated with disease. Often as not, these sorts of associations turn out to result from the disease, rather than the other way around. It is easily conceivable that there is a metabolic consequence of prostate cancer or even a metabolic predeterminate for developing prostate cancer, that causes higher levels in the bloodstream. Until a trial that randomizes fish oil intake is done, we have no idea whether it is causal, or an innocent bystander, in the development of prostate cancer.
Despite the limitations of the study, ACSH s chief supplement hater Dr. Josh Bloom says, The more you read, the worse the entire concept of dietary supplements looks. This is not surprising, since the legislation that provided supplements with immunity from FDA regulation (the Hatch Act of 1994) was so obviously anti-scientific and money-driven that it was inevitable that untested junk in a bottle would turn out to be useless and sometimes harmful.