Omega-3 fatty acids from fish are among the most potent heart-disease fighters that don't come in pill form, and loading up on three servings of fish per week is an easy way to get the recommended amount.
However, new research from Syracuse University casts some doubt about how beneficial those omega-3s are if you're getting them from contaminated fish. High levels of mercury in fish could interfere with your body's response to stress, which could promote inflammation, a leading cause of heart disease.
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The authors of the study looked at mercury levels and fish consumption patterns of 100 9- to 11-year-old children, analyzing blood lipids (the amount of healthy fat in the blood) and their levels of the stress hormone cortisol. Fifty percent of the children consumed fish on a regular basis, and all but one of the children had mercury levels far below that associated with possible health effects, as set by the Environmental Protection Agency.
Yet even with mercury levels that would normally be considered safe, Brooks Gump, PhD, associate professor in the department of public health, food studies and nutrition at Syracuse University and lead author of the study, noticed that as mercury levels in their bodies increased just slightly, the children were more likely to have "blunted" cortisol levels. While that sounds like a good thing, it isn't. Your body's cortisol levels naturally peak in the early morning and drop to their lowest point around midnight. Too much mercury in the system, Gump says, could interfere with that natural cycle, causing cortisol levels to remain depressed.
"One benefit of cortisol is that it's an anti-inflammatory response," he says. "One consequence of having that diminished ability to produce cortisol is that you're more likely to have an inflammatory response." High inflammation can lead to a host of chronic diseases, including diabetes, hypertension, heart attack, stroke, and cancer, and mental health problems such as depression, Alzheimer's disease, and dementia.
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Children with low levels of mercury exposure could be at a greater risk for these diseases as they get older, but it isn't just parents who should be concerned. "There's always the idea that kids are more vulnerable to mercury," Brooks says, "but I don't see any reason the effect wouldn't be the same in adults." More research, though, would be needed to confirm his suspicions, he adds.
Another disturbing finding from his study: The children who ate fish also had significantly higher lead levels than children who didn't. The scientists factored that in when looking at seafood and cortisol levels, so they don't believe that lead is contributing to depressed cortisol levels. However, previous studies have shown that high blood lead levels, accumulated over a lifetime of exposure, put women at greater risk of heart disease, high blood pressure, and stroke.
So should you keep eating fish—or feeding it to your children? "It's premature to recommend anything about eating, or not eating, fish," Gump says, adding that the fish-eaters in his study did have higher levels of good HDL cholesterol in their blood, suggesting the seafood was protecting their hearts in some way. "Ideally you'd be eating fish that don't have mercury," he says.
Here's the easiest way to find those:
• Say no to "big fish." In addition to tuna, the fish with the highest levels of mercury are usually the big predatory species, such as swordfish, king mackerel, and any kind of shark. But watch out for recreational species, as well. The U.S. Geological Survey has found dangerously high mercury levels in some freshwater species, including trout and bass.
• Seek out low-mercury tuna. Not all tuna are created equal. Tuna caught off the California coast is younger and has had less time to build up high levels of mercury than Atlantic and Gulf Coast tuna. And it has the bonus of coming from more sustainably managed fisheries. Look for American Tuna brand sold online through Heritage Foods USA. Other brands that sell this same type of tuna include Pacific Fleet, MaryLu Seafoods, Wild Planet, and Wild Pacific Seafood.
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• Or just forget tuna. If you can't find the safe tuna, try a safer fish to eat, such as omega-3-rich Wild Alaskan salmon or wild-caught Pacific sardines.
Read More: How to Cook with Sardines
Published on: February 2, 2012
Updated on: February 3, 2012