Omega 3 Fatty Acids and Cancer: Dissecting the Headlines this Morning
POSTED ON 7/14/2013 IN Archive BY Christopher Centeno
A connection between Omega 3 fatty acids and cancer has been big news of late. But don't ever believe the news headlines when they comment on only one salvo in a scientific pissing match. This week the headlines read that omega 3 fatty acids were associated with a higher prostate cancer risk based on this study
by Brasky from Ohio state. Based on those headlines, the readers of this blog are likely concerned about the high dose omega 3's that they're taking to replace the need for NSAID drugs like Motrin, Aleve, and Celebrex.
To understand a little more about the "behind the scenes" in the omega 3 fatty acid debate, a little background is needed. First Omega 3's are found in high concentrations in fish oil and in other plant sources. Ever since it was noted that Iceland Eskimo's, who were quite heavy, didn't suffer from many of the same diseases that were prevalent in the rest of the world, researchers wondered if it was the fish. They traditionally eat a a lot of fish and then put fish oil on their meals as if it were ketchup or salt. In addition, since Greenland is controlled by Denmark, the government has both populations in a socialized medical care system, where tracking data on disease is easier. Scientists eventually decided that it was the omega 3 fatty acids and their components like EPA and DHA that were helping the Eskimos avoid the chronic diseases that were so prevalent in the rest of the industrialized world. However, after two decades of glowing studies and press on the health benefits of fish oil, the pendulum was ripe for swinging the other way.
To fully understand what's happening, you also need to understand a bit about how our research system works. Researchers who rely on government funding make their careers by picking a topic and then submitting grants for that topic. In epidemiology research, where studies looking to find whether x is associated with y can take 3-10 years to complete and cost many millions of dollars, once you find a good topic, you often ride that one horse for your whole career. This is because it's easier to get the second grant in the same area and still easier to get the third, etc... The good news is this this allows for very bright people to deeply study a topic and tie up all of the loose ends on their theories. The bad news is that once a researcher gets funding on a topic, there's a tendency to want to get more funding on the topic. A great way to do that is to make a splash, like the one for fish oil and prostate cancer this week.
Enter the fish oil pendulum swing. The researcher who has published this week's paper has been adamant in the research journals that physicians aren't looking at fish oil hard enough. As an example, he laid down a challenge in a letter to the editor last year
, upset about a 2011 study that seemed to suggest that there wasn't a firm link between consumption of omega 3 fatty acids and cancer. This was likely because he had published an earlier 2011 study showing that high DHA in the blood
is associated with a greater prostate cancer risk.
Brasky's main research theme has been that most of the large dietary studies rely on a patient's memory of what they ate, which is a flawed way to see if food A causes disease B. To some extent that's true, but in well funded government studies like the kind that have been looking at fish oil benefits, the data is gathered by an army of people who track what people have eaten with meticulous care. Brasky believes that in the fish oil debate, it's better to measure the levels of certain types of oil metabolites in the blood and use these as a proxy for what the person ate. So if you eat more steaks with saturated fats, your blood metabolites should look one way and if you ate more fish or took more fish oil supplements, they should look another. The problem is that this approach opens up a new can of worms, like whether we really know enough about these profiles to predict consumption with the very high accuracy that would be needed.
So are there papers on the other side of the fish oil/cancer debate?
Absolutely. I've tried to summarize just the last few years of that research below. There's actually more than I have listed. so I'm just touching on the recent highlights.
This Harvard study
from February of this year found that eating more fish and omega 3 fatty acids
was associated with a lower risk
of fatal prostate cancer, while this Danish study
did find an association between more omega 3's in the blood and prostate cancer risk. This Wake Forrest lab study
showed that the DHA component of fish oil actually killed off prostate cancer cells. This earlier Harvard study
showed that while a high intake of saturated fat worsened prostate cancer survival, high omega 3 consumption improved prostate cancer survival
. This french study
from last year that looked at many different studies about many cancer types including prostate cancer concluded there wasn't enough evidence that omega 3's were protective or harmful, while this french study
concluded that the research showed that they were protective for cancer. A 2011 study by Aronson
showed that in a small randomized controlled trial, giving men with prostate cancer
fish oil supplements reduced tumor size after prostate cancer surgery
. This 2006 study
found that prostate cancer wasn't associated with omega 3 fatty acid consumption
. This 2006 JAMA study
that reviewed 38 other studies concluded, "A large body of literature spanning numerous cohorts from many countries and with different demographic characteristics does not provide evidence to suggest a significant association between omega-3 fatty acids and cancer incidence."
So getting back to the Eskimos, there's a burning question that may settle the debate with some authority. Do Greenland Eskimos who consume a traditional very high omega 3 diet have more prostate cancer? A 2008 study
showed that prostate cancer rates among "circumpolar" Inuits (Eskimos in many regions) were lower than non-Eskimos. What happens when Greenland Eskimos leave their traditional lifestyle and migrate to Denmark to live a more traditional industrialized lifestyle? This study
shows their prostate cancer rates go up. This study
going farther back in time also shows that Eskimos have a low prostate cancer risk and that when they take on the behaviors of the rest of the industrialized world, they develop the same cancers that we get. Perhaps you can't beat the title from this 2003 study
for a definitive answer on the fish oil and prostate cancer debate, "Inuit Are Protected Against Prostate Cancer". So much for the theory that fish oil causes prostate cancer!
After the break there's a bunch more on omega 3's and fish oil, most showing glowing benefits for fish oil and cancer risks. The upshot? There's research on both sides of this debate with most studies showing that fish oil is protective against prostate cancer. The best natural experiment we have in this regard is the Inuit populations that began this whole fish oil trend in the first place-they have a lower prostate cancer risk. However, even if Dr. Brasky is ultimately proven correct (a pretty big "if" given the other studies that argue against his thesis), the increased risk of prostate cancer of thirty some percent is dwarfed by the increased risk of a heart attack by taking NSAID drugs to help arthritis pain, which is several hundred percent! So for now, after having spent a few hours looking at the available data, I will definitely keep taking my fish oil and keep avoiding NSAIDs!
: This UNC Chapel Hill study
showed that consuming omega 3 fatty acids and non-fried fish was associated with a protective effect against pancreatic cancer. This Czech study showed
that having more omega 3's in the blood was associated with a lower risk of pancreatic cancer. This animal study found that omega 3 fatty acids delay the progression of pancreatic cancer.
: This study showed
that total omega 3 intake wasn't associated with breast cancer risk, but eating trans fatty acid (processed oils used to extend shelf life), Canola oil, and saturated fatty acids were associated with an increased breast cancer risk. This lab study also showed positive effects of omega 3's on human breast cancer cells, making estrogen that normal stokes the fire of breast cancer have less pro cancer effects.
: This meta-analysis of many other papers concluded that Omega 3 fatty acids had a solid body of evidence in patients with cancers of the blood. This study found that while eating bad processed oils (trans fatty acids) was associated with an increased risk of lymphoma, consuming omega 3 fatty acids was associated with a lower risk.
Skin Cancer: This Australian study
showed no relationship between omega 3's and skin cancer. This lab study found that high concentrations of Omega 3's inhibited cell cancer cells (melanoma) in-vitro. This one found that the metabolites of the fish oil component DHA also decreased tumor growth.
: This Aussie study
showed no increased risk of ovarian cancer from neither Omega 3's nor omega 6 fatty acids.
: This very large meta-analysis
of other studies suggested a lower risk with omega 3 fatty acid consumption. This colonoscopy based study
found that higher consumption of omega 3s in women is associated with less polyps.
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