THURSDAY, Nov. 21, 2013 (HealthDay News) -- Mercury levels in American women of childbearing age have dropped about one-third over a decade, a new federal study shows.

It's likely the trend can be attributed to women making more informed choices about what types of seafood are safer to eat, health officials said.

An analysis of national data found that blood mercury levels among women in this age group dropped 34 percent between 1999 and 2010, according to the U.S. Environmental Protection Agency.

The EPA also found that the percentage of women of childbearing age with blood mercury levels above the "level of concern" fell 65 percent during the study period.

Even so, there was little change in the amount of fish eaten by women between 1999 and 2010. The decrease in mercury levels suggests that women may have started eating types of fish with lower mercury levels, the EPA said in an agency news release.

The agency noted that fish and shellfish are an important part of a healthy diet. These foods are a source of high-quality protein, many vitamins and minerals, omega-3 fatty acids, and are mostly low in saturated fat. A well-balanced diet that includes a variety of fish and shellfish can be good for heart health and children's growth and development.

However, nearly all fish and shellfish contain traces of mercury. For most people, the risk from mercury by eating fish and shellfish is low, the agency noted. But some fish and shellfish contain higher amounts of mercury that may harm an unborn baby or a young child's developing nervous system. The risks depend on the amount of fish and shellfish eaten and the levels of mercury in the fish.

Women who may become pregnant, pregnant women, nursing mother, and young children should avoid some types of fish, but continue to eat fish and shellfish that are low in mercury, the EPA and U.S. Food and Drug Administration recommended.

The agencies offered the following advice:

  • Do not eat shark, swordfish, king mackerel or tilefish -- they have high levels of mercury.
  • Eat up to 12 ounces (two average meals) weekly of a variety of fish and shellfish that are low in mercury. Five of the most commonly eaten are shrimp, canned light tuna, salmon, pollock and catfish.
  • Albacore ("white") tuna has more mercury than canned light tuna. So, when choosing two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.
  • Check local advisories about the safety of fish caught in local lakes, rivers and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish caught from local waters. Don't consume any other fish during that week.
  • Follow these recommendations for young children, but serve smaller portions.

More information

The U.S. Environmental Protection Agency has more about mercury in seafood.