The minefields that are meta-analyses came into fuller view as an omega-3 expert dissected the infamous omega-3 / prostate cancer study at the Council for Responsible Nutrition’s annual conference earlier this month.
The type of study known as a meta-analysis is when researchers look at a group of studies already conducted to try to come to larger truths about how a substance might work. Although sometimes effective, the risk lies when studies do not all look at the same end points, with the same population, with the same dosage, with the same time frame. And that’s not to mention potential researcher bias.
William Harris, Ph.D., a research professor at the Sanford School of Medicine at the University of South Dakota, is an omega-3 expert who developed the Omega-3 Index – a measure of the omega-3 fatty acids EPA and DHA present in red blood cells. He gave a session at the CRN conference, dissecting in particular the meta-analysis finding that omega-3s led to increased prostate cancer incidence. The study is thought responsible for the large drop-off in consumers purchasing omega-3 supplements.
To see what the industry is doing to counter the downturn, and how to position your brand for success, check out the Nutrition Business Journal / Engredea report on the omega-3 market here.
To recap, the study gave another look at data compiled in the SELECT Trial, which looked at selenium and vitamin E on prostate cancer incidence. (There was nothing positive found, although the researchers used selenomethione and not high-selenium yeast, which is thought to be a significant factor.) Researchers went back to the blood work and looked at omega-3 status and prostate cancer incidence. The researchers concluded, “This study confirms previous reports of increased prostate cancer risk among men with high blood concentration of PUFAs.”
“The entire problem is interpretation,” said Harris. “Association does not mean causation. That should be the first thing a reporter should ask on TV. But they never asked it.”
Harris said the control group had omega-3 index equivalents of 3.62 percent, while the index was 3.67 percent in the low-grade cancer group and 3.74 percent in the high-grade cancer group.
“These are not high omega-3 levels by any means,” said Harris. “The study did not track fish intake nor supplement use. To say supplements caused it is irrational.”
Harris noted other significant studies that belie the notion that omega-3s cause prostate cancer.
- No increase in prostate cancer incidence was seen in eight randomized controlled trials with omega-3 fatty acids.
- Other studies report higher omega-3 or fish intake is associated with reduced prostate cancer risk.
- The risk for death from cardiovascular disease is eight times higher than the risk from prostate cancer.
- The prostate cancer incidence in Japan – where fish consumption is high – is considerably lower than in the U.S.
Finally, a more recent meta-analysis, from September 2014, concluded there is “no strong evidence that circulating fatty acids are important predictors of prostate cancer risk.”
“This study did not make it onto evening news reports because they are not sensational,” Harris said.