Mothers’ increased consumption of fish before and during pregnancy leads to increased exposure to both mercury and the long-chain omega 3 DHA. Mercury may negatively affect brain development in one’s unborn baby, whereas DHA may stimulate brain development. However, the negative effect of mercury may outweigh the beneficial effect of DHA for most species of fish (see Mercury vs. Omega-3s for Brain Development).
Unfortunately, women of childbearing age (18 to 45) appear less aware and knowledgeable about this problem than other women, despite FDA and EPA campaigns to inform every OB/GYN and pediatrician in the country about the potential risks of mercury in fish.
Since mercury sticks around in the body, women may want to avoid fish with high levels of mercury for a year before they get pregnant, not just during pregnancy. The rationale for avoiding fish for a year before pregnancy is because the half-life of mercury in the body is estimated to be about two months. In a study I profile in the above video, a group of researchers fed subjects two servings a week of tuna and other high mercury fish to push their mercury levels up, and then stopped the fish at week 14. Slowly but surely their levels came back down. I know a lot of moms are concerned about exposing their children to mercury containing vaccines, but if they eat just a serving a week or less of fish during pregnancy, the latest data shows that their infants end up with substantially more mercury in their bodies than if they were injected with up to six mercury-containing vaccines.
Given the two-month half-life, within a year of stopping fish consumption our bodies can detox nearly 99% of the mercury. Unfortunately the other industrial pollutants in fish can take longer for our body to get rid of. Certain dioxins, PCBs, and DDT metabolites found in fish have a half-life as long as ten years. So getting that same 99% drop could take 120 years, which is a long time to delay one’s first child.
The fact that we can still find DDT in umbilical cord blood decades after the pesticide was banned speaks to the persistence of some pollutants.
What effects do these other pollutants have? Well, high concentrations of industrial contaminants are associated with 38 times the odds of diabetes—that’s as strong as the relationship between smoking and lung cancer! Isn’t diabetes mostly associated with obesity though? Well, these pollutants are fat-soluble, so “as people get fatter the retention and toxicity of persistent organic pollutants related to the risk of diabetes may increase.” This suggests the shocking possibility that obesity “may only be a vehicle” for such chemicals.
Now the pollutants could just be a marker for animal product consumption, which may be why there’s such higher diabetes risk, since more than 90% of the persistent organic pollutants comes from animal foods. And indeed, in the U.S. every additional serving of fish a week is associated with a 5% increased risk of diabetes, which makes fish consumption about 80% worse than red meat. PCBs are found most concentrated in fish and eggs (Food Sources of PCB Chemical Pollutants), which may be why there are lower levels of Industrial Pollutants in Vegans.
Michael Greger, M.D.
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