Study: Eating fish is OK, despite mercury

University researchers are garnering international attention for a study that shows that eating lots of fish poses no detectable health risk from mercury ingestion.

Even though the world's fish contain slight amounts of mercury, eating large quantities of fish won't hurt if the fish contain low levels of the substance. The study, the most comprehensive done on the subject to date, gives the green light even to very young children and pregnant women.

The nine-year University study was conducted in the Republic of the Seychelles, an island nation in the Indian Ocean where most people eat nearly a dozen fish meals each week and have mercury levels about 10 times higher than most U.S. citizens'. Indeed, no harmful effects were seen in children at levels up to 20 times the average U.S. level. The work is published in the August 26 issue of the Journal of the American Medical Association.

"We look at the Seychelles people as a sentinel population," said pediatric neurologist Gary Myers, who examined the children. "If somebody who eats fish twice a day does not show effects from mercury exposure, it's unlikely that somebody who eats fish twice a week will be affected. And the fish they eat in the Seychelles contains the same amount of mercury as fish sold at supermarkets and eaten in the United States."

Added first author Philip Davidson, an expert on developmental disabilities who designed a battery of the most sophisticated tests available to examine the children: "What we found in the Seychelles is applicable to every woman, every man, and every child around the world who eats ocean fish."

In the United States, the findings apply only to fish bought and sold commercially, at grocery stores, supermarkets, fish shops, and in restaurants. Those fish are already regulated based on their mercury levels, and current regulations are sufficient to safeguard frequent fish eaters against mercury exposure, say the investigators.

The Seychelles study began in 1989, when Rochester researchers, with decades of expertise studying mercury exposure, chose the nation of about 65,000 people as an ideal site to study the effects of mercury exposure. Myers enrolled 779 newborn children, about half the births on the islands that year. From the children's mothers, Myers and the team took samples of hair, which lock in a record of mercury exposure of the child during gestation.

Experts then studied the children by visiting their homes, talking to their parents, and performing nearly three dozen sensitive developmental and neurological tests designed to detect subtle effects of mercury exposure. The analysis included noting when the children learned to walk and talk, measurements of reflexes, word recognition, and social behavior, and the best neuropsychological tests yet developed to evaluate children at these ages. At each interval, the results of the longitudinal study have been consistent: no ill effects from a high-fish diet. The JAMA paper details the 66-month evaluation, which included 711 of the original children.

Mercury is a deadly neurotoxin that at high levels kills nerve cells, causing blurry vision, lack of coordination, slurred speech, and even death. Children exposed to high levels of the compound pre-natally can suffer slowed development, blindness, cerebral palsy, and other birth defects.

While high amounts of mercury are obviously toxic, scientists for years have debated the health effects of lower levels. Last year, the federal Environmental Protection Agency proposed slashing the amount of mercury that is acceptable for people to ingest from 30 micrograms per day to six, which could remove from the market a significant proportion of the fish now available, such as swordfish, shark, red snapper, and tuna.

Rochester scientists fear lower levels might also persuade consumers to limit their intake of fish, a remarkably healthy form of nutrition.

"Eating lots of ocean fish isn't much of a hazard compared to missing out on the benefits from not eating fish," said Thomas Clarkson, professor of environmental medicine and an internationally recognized authority on mercury. Clarkson is principal investigator of the study, which is being funded by the National Institutes of Health, the Food and Drug Administration, and the Republic of the Seychelles.

Besides Clarkson, Davidson, and Myers, the team also included Christopher Cox, associate professor of biostatistics; University researchers Catherine Axtell, Jean Sloane-Reeves, Elsa Cernichiari, Anna Choi, and Yining Wang; and researchers at other institutions.