It's no secret that mercury in fish is bad for your health. Ill effects ranging from low IQ, ADHD, and autism in children have been well documented, but emerging research suggests that eating too many meals of tainted fish could lead to other common, yet unexpected, diseases in adults, too.
Could lupus and rheumatoid arthritis be fueled by mercury-infused fish? A new study published in the journal Environmental International suggests that just might be the case. Researchers looked at a large group of women and discovered that higher levels of mercury in the body correlated to higher thyroid antibodies. These thyroid antibodies are most notably elevated in women who live with autoimmune diseases like lupus and rheumatoid arthritis, painful conditions in which the immune system starts attacking healthy tissue.
Mercury, a heavy metal, has been shown to accumulate in the human thyroid gland, but experts say more research is needed to figure out exactly how mercury affects the thyroid and alters our ability to be healthy. Until that happens, if you eat fish, seek out species that are lower in mercury buildup—current "safe" levels may be too high—and high in omega 3s to boost your health. "This study suggests the possibility of risks at levels of mercury in the blood below what is currently considered safe," says study author Carolyn Gallagher, PhD candidate in the department of preventive medicine at Stony Brook University in New York.
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Mercury in fish could mean bad news for your ticker, too. Although many fish are packed with heart-disease-fighting omega-3 fatty acids, mercury contamination could cancel out that benefit and even increase your risk of suffering a heart attack. A 2012 study from Syracuse University found that high mercury levels in fish could throw off your body's natural response to stress, increasing inflammation, a leading cause of heart disease.
Interestingly, even levels of mercury considered "safe" caused an unnatural change in cortisol levels. Although cortisol is considered a stress hormone, its natural ebb and flow throughout the day helps protect against inflammation. When mercury blunts cortisol levels in the body, inflammation—and heart disease—can flourish. Children who have routinely depressed cortisol could face an increased risk of heart problems as they age.
Mercury in a pregnant or nursing mother's diet may not only affect her child's IQ, but also could create a predisposition for childhood eczema, according to a 2010 study published in the journal Environmental Health Perspectives.
Eczema, an itchy skin allergy characterized by an irritating, red raised rash, is more common in children whose mothers ate a diet higher in mercury while breastfeeding, and in children with higher levels of mercury in their systems.
Here's what you need to know about choosing safer seafood.
• Look for the right tuna. Tuna is rich in healthful omega-3 fats, but some species are endangered, are high in mercury, or both. However, experts have found that albacore tuna caught in waters off the western coasts of the U.S. and Canada is lower in contaminants. Greenpeace named Wild Planet Foods' albacore tuna No. 1 in terms of sustainability; the tuna is also much lower in mercury compared to other brands.
• Know your supplements. Some fish-oil supplements will list the source of the oil on the label. Choose brands that use smaller fish, such as sardines, anchovies, or mackerel, as the oil source; this will reduce your contamination (smaller fish are lower on the food chain, thus less contaminated).
• Avoid heavily tainted species. Salmon seems like a good choice for low contamination and high omega-3 content, but be sure to steer clear of unsustainable, often-tainted farmed salmon. To satisfy your salmon fix, choose wild-caught Alaskan salmon. The population is stable and tends to be lower in contaminants.
• Choose fish from the list. For advice on the safest, healthiest fish to eat, check the superfish list compiled by Food & Water Watch.