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Study Links Great Lakes Fish and Diabetes
Produced by Gabriel Spitzer on Sunday, August 16, 2009
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Epidemiologist Mary Turyk shows the molecular structure of persistant organic pollutants found in Great Lakes fish. (WBEZ/Gabriel Spitzer) |
Scientists have known for a long time that a lot of wild-caught fish have dangerous contaminants. People who eat fish have to weigh the health benefits against the risks of consuming those pollutants. Now some new research could make that balancing act even trickier. It links diabetes to an old chemical many assumed was long gone.
In the early morning hours, anglers gather on Chicago’s Navy Pier. Ray Penn is practically within casting distance of the downtown skyscrapers. He dips his line in the waters of Lake Michigan, hoping to pull out something tasty.
PENN: I fry ‘em, yeah. They got a little bit of bones in ‘em, but – oh yeah. Oh, yeah, baby! I felt that!
It’s looking like a good morning for rock bass.
PENN: See, there’s a bass on the end of this. This is a small bass, now this guy here, he’s edible.
Penn says he eats fish a couple of times a week, without giving it a second thought. Down the pier, Patrick Duhan has the same attitude.
DUHAN: This is the Great Lakes! It’s such a big body of water. It’s almost like the ocean. They throw tons of crap in the ocean, and there’s just too much of it to screw up.
But scientists say people have managed to screw up the Great Lakes a fair amount. Epidemiologists have been studying a group of sport fishers, like these guys, and charter boat captains, who eat a lot of Great Lakes fish. Mary Turyk of the University of Illinois at Chicago measured the contaminants in their blood, and tracked their health over the years.
TURYK: We found we had 36 cases of new diabetes. And what we found was that DDE, the metabolite of DDT, was related to diabetes incidence.
DDT: That’s the pesticide made infamous by Rachel Carson’s book, Silent Spring. DDE is produced when it breaks down. The chemical was banned in 1972, but traces of it are still all over the place, including in fish. And like mercury or PCBs, it concentrates as it moves up the food chain. So you don’t have to eat much.
TURYK: The captains were eating, I think, on average, a meal a week.
SPITZER: One meal a week?
TURYK: Yeah.
SPITZER: That doesn’t seem outlandish or anything.
TURYK: No, it doesn’t. It doesn’t at all. In fact, recommendations from the FDA for eating fish, based on mercury levels, are two meals per week, for pregnant women.
So just half that much fish was linked to about a 33 percent increase in diabetes cases in this small sample. Turyk says it’s not clear how DDE or DDT might contribute to diabetes. It might have to do with effects on hormones or the immune system.
TURYK: We really need more basic science to determine mechanisms that might be responsible for this.
Another unknown is just how dangerous might this be, and when does it start to outweigh the advantages of eating an otherwise healthy food? Tamarah Duperval is a family doctor at a West Side Chicago clinic. She says she still tells people to eat more fish.
DUPERVAL: In our population, it’s a great wonder and a challenge to try to present fish as an option, when primarily the staple of diet is either chicken or beef.
That population is mostly low-income and minority. She says about half are overweight or obese. From a nutrition point of view, those are exactly the people you’d want to be eating a lean, healthy protein like fish. So Duperval is concerned about sending mixed messages.
DUPERVAL: I do think it is confusing. And it’s in part I think how we communicate crisis in this country, especially when it comes to food safety. They miss the overall preventative message, that fish is good food, and it actually provides a lot of important nutrients that are lacking in their diets.
Health authorities, including the Illinois Department of Public Health, often issue advisories about certain fish that have a lot of pollutants. Duperval says understanding those warnings can help people avoid some of the hazards. But the diabetes research shows we may still have a lot to learn about these chemicals, so what’s safe to eat is getting harder to know.
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Samuel N. Grief, MD, Chicago // Monday, August 17, 2009 @ 10:48 AM
Fish is a double-edged sword: it is typically filled with heart-healthy fats and a variety of nutrients AND/OR may contain contaminants such as PCBs, dioxins or other chemicals, such as DDE.
Be that as it may, fish is still an important component in most people's diet and should be consumed at least once weekly, depending on one's gender, age and overall health needs.
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Lin Kaatz Chary, PhD, MPH, Gary, IN // Monday, August 17, 2009 @ 2:33 PM
This research is incredibly important, and I also agree that the message to folks about fish can be very confusing. I would like to see more MDs and other health providers become more informed and interested in how the environmental impacts of toxics affect their patients' diets. Along with encouraging patients to eat fish, doctors can also give guidelines and easily available information about which fish are best, how to clean fish, how often to each certain fish and so forth. And they could also use their considerable political clout to be more active in the fight for more stringent environmental regulations and virtual elimination (on power plants and mercury, which ends up in fish, for example) which could make real change.
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Carolyn Baker, Albany Park / Chicago // Tuesday, August 18, 2009 @ 8:00 AM
Thank you Dr. Chary! It's not only about whether or not to eat fish, but about not assuming the lake, which is our water, our food, our world, is 'too big to screw up'
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Concerned Subscriber, Chicago, IL // Tuesday, August 18, 2009 @ 5:34 PM
I agree with Sam and Lin as far as they go.
The destruction of our global fisheries is travesty that can be halted and at least partially reversed if we have the political will.
Diabetes is a huge, expensive and growing public health and economic problem.
Unfortunately, this study is way too small (36 cases) to draw any meaningful scientific link between eating polluted fish (clearly bad) and diabetes. And, to the extent that it draws attention away from proven links, that people can do something about, like diets high in overly processed foods and insufficient exercise, it may be doing public health a big disservice.
NPR is not doing the public proper service by airing this kind of fluff science story without proper disclaimers about statistical validity. Frankly, given the lack of statistical meaningfulness it is questionable whether this story even meets NPR’s normally high journalistic standards.
People are confused enough about these complex issues without NPR casually contributing to the problem by airing stories that further confuse the issues by generating more heat than light.
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Caroline McNabb, Muskegon, Michigan and Costa Mesa, CA // Wednesday, August 19, 2009 @ 2:14 PM
I grew up on Lake Michigan and witnessed a massive fish die-off of the 70's. Thousands of fish lay dead on the beaches. I would never eat fish after that. To see the fish die off in such great numbers unnaturally, perhaps due to being poisoned in the waters was horrific. If you had seen it, you would never have eaten fish again either. Chemicals and contaminants in water were unregulated for long enough to such damage that I believe most bodies of water will never be the same. How sad. Chemical discharges may be regulated now, but the damage has already been done.
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Gabriel Spitzer, Chicago // Monday, August 24, 2009 @ 2:37 PM
I respect Concerned Subscriber's point, and appreciate his/her emphasis on the importance of statistical confidence in scientific data. To be sure, this study was relatively small (though not out of the norm for this sort of longitudinal research), but I think dismissing the number of cases and the research in general as "fluff science" misses the mark.
First of all, the overall study group was decently large, at 471. In establishing an association between two phenomena -- say, levels of a chemical in people's bodies and the incidence of diabetes in that group -- statisticians use a number called the "p value." Generally, anything under .05 is considered statistically significant, and the lower the number, the more solid the significance. The association between diabetes incidence and DDE levels in this study had a "p value" of .008, meaning the statistical significance is quite robust.
These results also corroborate other research out there, including a number of cross-sectional studies.
So, even though this particular paper, published in a peer-reviewed journal, is not airtight proof of a correlation, it's pretty strong evidence which, we judged, was worth reporting to the public.
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