Children whose mothers regularly ate mercury-contaminated ocean fish during pregnancy do not have an increased risk of developmental problems. But in an editorial in the journal, an expert from the Environmental Protection Agency cautions that more research is needed to confirm this finding. Mercury can cause brain damage; and prenatal exposure can be particularly damaging to the developing brain. Previous studies have found that children whose mothers were exposed to extremely high levels of mercury during pregnancy were more likely to be mentally retarded and developmentally delayed.
Thanks to industrial dumping, virtually all ocean fisheries are contaminated with mercury to varying degrees. Whether prenatal exposure to lower levels of mercury can hamper mental development is controversial. Several studies have come to different conclusions. In the current study looked at more than 700 children and their mothers in the Republic of Seychelles, an Indian Ocean archipelago where 85% of the population eat fish daily. To determine how much mercury the children had been exposed to before birth, the researchers checked levels of the metal in their mothers' hair, testing sections of hair that grew during pregnancy.
On average, the mothers had mercury levels of 6.8 parts per million (ppm) in their hair during pregnancy, and the children had levels of 6.5 ppm in their hair at age 5-1/2. According to the World Health Organization, the "lowest toxic level in hair" is 5 ppm. Most of the fish the researchers tested contained mercury at levels between 0.05 and 0.25 ppm -- roughly the levels found in fish caught and sold in the US. In the US, many fisheries are contaminated not only with mercury but with other toxins, including PCBs, which are known to have adverse effects on the developing brain. Consequently, many states advise pregnant and nursing women and young children to limit or forego fish from local waters. Women should follow state guidelines when deciding whether to eat fish during pregnancy and whether to feed fish to their children.
The Journal of the American Medical Association August 26, 1998;280:701-707, 737-738.
COMMENT: I think it is very important to restate the following statement "Thanks to industrial dumping, virtually all ocean fisheries are contaminated with mercury to varying degrees." This is the main reason why I caution people not to eat much fish. As mentioned in the above article, it would be much wiser to use molecularly distilled fish oil as a supplement. One reason why this study might be providing false reassurance regarding eating fish, though, is that they used hair analysis to show if mercury were present. This is a COMMON misconception. Mercury will not show up in the hair unless it is first in the blood. It binds very tightly to sulfur in the body tissues. It only goes into the blood when it is being absorbed or eliminated. So, unless you are in one of the active, phases the hair levels will not reflect mercury levels. Unfortunately, outside of a chelation challenge or an energy measuring system, measuring mercury levels is extraordinarily difficult to do. The other consideration is this: if the EPA is so concerned about mercury in fish, why aren't they warning us about the mercury in amalgam fillings? There is no question that the mercury in a woman's "silver" fillings is transferred through the placenta to her fetus.