Pregnant women should eat fish but avoid seafood high in mercury levels, according to a new study showing that maternal fish consumption during pregnancy is linked to better cognitive skills in infants, while high mercury levels are linked to poorer cognitive performance.
Emily Oken and colleagues studied the relationship of seafood, mercury, and infant cognition using subjects from Project Viva, a large-scale prospective study of pregnancy and infant development. The researchers acquired data about the dietary habits of 135 pregnant women and measured the women's mercury levels using hair samples. They then tested the women's infants at six months of age, using a visual recognition memory (VRM) test that is highly predictive of later IQ.
The researchers report, "For each additional weekly fish serving, offspring VRM score was 4.0 points higher. However, an increase of 1 ppm [part per million] in mercury was associated with a decrement in VRM score of 7.5 points." VRM scores were highest in infants whose mothers ate fish more than twice a week but had mercury levels below 1.2 ppm, a finding that remained true when the researchers controlled for a wide range of sociological and biological variables.
"It may seem contradictory that, on the one hand, fish intake raises mercury levels and higher mercury levels lead to worse cognition but, on the other hand, higher fish consumption is associated with better cognition," Oken and colleagues say. "The most likely explanation is that the benefit is conferred by consuming fish types with the combination of relatively little mercury and high amounts of beneficial nutrients."
"Maternal fish consumption, hair mercury, and infant cognition in a U.S. cohort," Emily Oken, Robert O. Wright, Ken P. Kleinman, David Bellinger, Chitra J. Amarasiriwardena, Howard Hu, Janet W. Rich-Edwards, and Matthew W. Gillman, Environmental Health Perspectives, Vol. 113, No. 10, October 2005. Address: Emily Oken, Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim, 133 Brookline Avenue, Boston, MA 02215, email@example.com.