FRIDAY, May 14, 2004 (HealthDayNews) -- Adding a new wrinkle to the long-running debate over the safety of fish consumption by pregnant women, British researchers are reporting that fish appears to boost the weight of newborn babies.
The findings, which contradict previous studies linking consumption of fish oil to longer pregnancies but not bigger babies, add "to the evidence that fish is an important part of the human diet," said study co-author Imogen Rogers, a researcher at University of Bristol in England.
However, a U.S. environmental watchdog organization continues to advise American women to stay away from most fish if they're pregnant or thinking about having a child. The risk from mercury in the fish is just too large, contends the Washington D.C.-based Environmental Working Group.
Indeed, the U.S. government advises pregnant women and young children to avoid a number of types of fish, including shark, swordfish, king mackerel, and tilefish.
The British researchers studied 11,585 pregnant women in southwest England who completed surveys about their fish consumption. The mean consumption of fish per day was 33 grams -- the equivalent of one-third of a small can of fish, Rogers said. Most of the fish eaten was whitefish. About a third was oily fish (a category that includes tuna and swordfish), and 6 percent was shellfish. The researchers didn't ask if the fish was canned or fresh.
They report their findings in the June issue of the Journal of Epidemiology and Community Health.
Women who didn't eat fish were 1.37 times more likely to give birth to under-weight infants than those who ate the most fish. The researchers didn't find any link between fish consumption and length of gestation, the period between conception and birth.
Bigger babies tend to be healthier babies, Rogers said. "Small babies and premature babies are at greater risk of suffering from a number of health problems. There is also evidence that small babies are more likely to develop a number of diseases as adults, including coronary heart disease and diabetes."
Researchers have been studying possible links between fetal development and maternal fish consumption for at least 20 years, Rogers said. "One of the things that gave scientists the idea that there might be a connection was that island populations with a lot of fish in their diet, such as the Faroe and Orkney islanders, had relatively high birth weights," she said. Both groups of islands lie off the coast of Scotland.
Oddly, studies tended to link consumption of fish oil supplements to longer pregnancies, while the eating of fish itself appeared to contribute to bigger babies, she said.
While the study findings need to be confirmed, they reinforce British recommendations that pregnant women eat two portions of fish -- including one portion of oily fish -- per week. Women should avoid fish that are high in mercury, like swordfish and marlin, and limit consumption of tuna for the same reason, Rogers said.
"However, most fish are relatively low in mercury, and the possible dangers of low level mercury consumption need to be balanced out against other possible benefits from eating fish," she said.
Despite such recommendations, the debate over fish consumption and pregnancy continues to flare. Some studies suggest that mercury in fish contributes to brain defects; other studies fail to find a connection. One thing appears to be clear, however: women who eat more fish consume more mercury. Mercury levels are almost four times as high in women who eat at least three servings of fish a week compared to those who eat no fish, some studies have shown.
While fish is good for most people, pregnant women should avoid it on the whole, said Richard Wiles, senior vice president of the Environmental Working Group. "Unfortunately, we've contaminated this wonderful food source with a very toxic metal. We wish women could eat fish freely and not worry about mercury, but that's not the smart thing to do."
Wiles said some fish appear to be safe, including wild salmon and farm-raised trout and catfish.
"But," he added, "it's tough to say. We just don't have good information on it and the government isn't providing it. For women, the best advice is to moderate your consumption and eat a variety of fish. Don't eat albacore tuna at all. If you're going to eat chunk light tuna, we're recommending no more than a can every two weeks if you're pregnant or you're even thinking about getting pregnant."