To Your Health

Does the mercury content in fish make it unsafe to consume while pregnant?

Q. I want to have another baby but it seems that there are so many more recommended dietary restrictions now compared to eight years ago when I had my first baby. I am especially worried about mercury in fish, but fish is also a good source of the omega-3 fatty acids that are so important for babies. Should I just stop eating fish while I am pregnant?

A. The warnings about mercury consumption during pregnancy may give you the impression that you should avoid fish altogether while you're pregnant, but remember that fish is an excellent and easy-to-prepare source of protein, vitamins, and omega-3 fatty acids, all essential for your baby's total development. A bit of good news comes in an article in the medical journal Epidemiology (July 2004) reporting that fish intake during pregnancy, even at twice the recommended frequency, was associated with increased developmental scores in the baby. Apparently the ill effects of mercury were more than offset by the benefits of the nutrients in fish. Most Americans desperately need more of the omega-3 fatty acids found generously in fish, but the need is highest in infants, both in the uterus and for several years after birth.

The damage from mercury comes from its competition with nutritional minerals, especially selenium. Selenium is part of our vitally important antioxidant protection system. Simultaneous high mercury exposure and low selenium intake leads to damage to fats by oxygen. These fats are particularly important in brain development in infants, but adults still need these "good" fats to protect against atherosclerosis and other diseases of aging. Selenium intake needs to stay within a narrow range, so you should seek professional advice before you add it as a supplement.

If you are concerned about unavoidable mercury intake, you can add a supplement of N-acetyl cysteine. NAC is an amino acid used by our bodies to make glutathione, which is perhaps our most important antioxidant but not easy to supplement directly. Supplementation with NAC enhances the body's own production of glutathione, plus NAC tends to combine with mercury to enable the body to excrete it more easily.

Because it is distilled and thus purified, pharmaceutical-grade fish oil is not a major source of mercury and this supplement can be safely used. As a bonus it does not produce the "fishy burp" so objectionable to many people. Two capsules provide about the same amount of omega-3 fatty acids as one serving of salmon. If you enjoy fish, the Food and Drug Administration lists the mercury content of commercial fish on a Web site, www.cfsan.fda.gov/~frf/sea-mehg.html. With this information you can choose to eat only fish with the lowest mercury content.

For peace of mind, you might consider a hair mineral analysis for both toxic and nutritional minerals. Hair mercury level is the best measure of long-term mercury accumulation in your body, which would give you an idea of how strict you should be in avoiding mercury. It is less accurate for judging whether you need to add nutritional minerals such as selenium, and quite worthless for measuring selenium if you have recently used a selenium-containing anti-dandruff shampoo. Very specialized tests are required to evaluate your need for NAC.

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