Fish and Pregnancy

Fish and Pregnancy

A large percentage of society has poor understanding of the benefits and serious concerns about the dangers of fish consumption particularly in women who are pregnant or would be pregnant. This was addressed by Dariush Mozaffarian (from Harvard School of Public Health) reviewed in a meta-analysis all the studies until 2006.¹

Mercury is a reactive heavy metal emitted from natural sources (volcanoes) and human sources (coal-fired electric power plants, gold mining, institutional boilers, chlorine production, and waste incineration). From the atmosphere, mercury cycles from rainwater into lakes and oceans, where it is converted by microbial activity into organic methyl mercury, which is readily absorbed and actively transported into tissues.¹

Concentrations of methyl mercury in fish depend on levels of environmental contamination and on the predatory nature and lifespan of the species. Larger, longer-living predators (e.g., swordfish, shark) have higher tissue concentrations, while smaller or shorter-lived species (e.g., shellfish, salmon) have very low concentrations.¹

Methyl mercury crosses the placenta, and fetal exposure correlates with maternal exposure. Marked neuro developmental abnormalities occur in children following very high gestational exposure. For example, maternal consumption of highly contaminated fish resulted in 10-30 ppm mercury from industrially polluted Minimata Bay, Japan, in the 1950s. The consumption of contaminated grain (maternal intake >50,000ug/per day in 1971 in Iraq) resulted in very high mercury levels in maternal hair (18-598 ppm).¹

For comparison, in US women of childbearing age, median levels of mercury in hair were 0.19 ppm overall and 0.34 ppm among women consuming 3 or more servings of fish per month. These exposure levels do not produce neuro developmental deficits.

DHA appears important for early neurodevelopment. Consumption of fish is <6 oz/wk for 74% of women of childbearing age and 85% of pregnant women. Therefore, these women should consume an adequate amount of fish —12 oz/wk to provide reasonable amounts of DHA and avoid further decreases in already low seafood intake.

Women who are or may become pregnant and nursing mothers should avoid selected species (shark, swordfish, golden bass, and king mackerel; and limit intake of albacore tuna to 6 oz/wk) to minimize methyl mercury exposure.

The Environmental Protection Agency (EPA) has published a focused advisory for women of childbearing age, nursing mothers, and young children. (www.cfsan.fda.gov) The allowable upper limit of intake for methyl mercury is 50 µg/wk for a 70-kg woman. The document specifically advises such individuals to:

Avoid tile fish, swordfish, shark, and king mackerel, since these fish contain >50 µg methyl mercury per serving.

To eat up to 12 oz/wk (2 average meals) of a variety of fish and shellfish lower in mercury, including up to 6 oz/wk of albacore tuna (30 µg methyl mercury per serving).

This advisory was not intended for the general population and in most adults, the benefits of consuming oily fish rich in omega-3 polyunsaturated fatty acids (PUFA) far outweighs the risks).¹

Risks of PCBs and Dioxins

Dioxins—commonly referring to dibenzodioxins and dibenzofurans—are toxic by-products of waste incineration, paper bleaching, pesticide production, and production of polyvinyl chloride plastics.¹

PCBs are synthetic compounds previously used in industrial and commercial processes. When PCBs and dioxins were measured in farmed and wild salmon, levels were similar to those in several other foods (beef, chicken, pork, dairy products, and vegetables).

In short, levels of PCBs and dioxins in fish are low, similar to those in several other foods, and the magnitudes of possible risks in adults are greatly exceeded by benefits of fish intake. Farmed and wild salmon contain substantial levels of n-3 PUFAs: 4504mg of EPA and 1774 mg DHA per 6 oz portion.¹

Sources

1. Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health: evaluating the risks and the benefits. Jama. Oct 18 2006;296(15):1885-1899.