A study of Danish mothers and infants finds that infants benefit from physical and cognitive development when the mother eats fish when pregnant. Longer breastfeeding also benefits baby.
Fears of mercury levels in fish have led to American women being advised to keep their fish consumption to a minimum, but this study recommends that pregnant women eat low-mercury fish—cod, plaice, salmon, herring and mackerel—at least three times a week. Additionally, the study reinforces existing evidence that breastfeeding is beneficial to an infant’s development.
“These results, together with findings from other studies of women in the U.S. and the United Kingdom, provide additional evidence that moderate maternal fish intake during pregnancy does not harm child development and may on balance be beneficial,” said Assistant Professor Emily Oken, lead author of the study.
Researchers from the Department of Ambulatory Care and Prevention of Harvard Medical School and Harvard Pilgrim Health Care and the Maternal Nutrition Group from the Department of Epidemiology at Statens Serum Institut in Copenhagen, Denmark, conducted the study. It was published in the September issue of American Journal of Clinical Nutrition and confirmed that the omega-3 fatty acids in fish, and breast milk compounds benefit infant development.
The study reviewed 25,446 children born to pregnant women enrolled from 1997—2002 in the Danish Birth Cohort. Participants were asked about child development markers at 6 and 9 months postpartum, and breastfeeding at 6 months postpartum. Prenatal diet, including amounts and types of fish consumed weekly, was assessed by a detailed food frequency questionnaire administered when they were six months pregnant.
Mothers were asked about their infants’ specific physical and cognitive development markers at 6 months, eg. holding up his/her head, sitting with a straight back, sitting unsupported, responding to sound or voices, imitating sounds, or crawling. More advanced markers were checked at 18 months – could the child hold up his/her head, sit with a straight back, sit unsupported, respond to sound or voices, imitate sounds, or crawl.
The children whose mothers ate the most fish during pregnancy were more likely to have better motor and cognitive skills. For example, among mothers who ate the least fish, 5.7% of their children had the lowest developmental scores at 18 months, compared with only 3.7% of children whose mothers had the highest fish intake. Compared with women who ate the least fish, women with the highest fish intake (about 60 grams—2 ounces—per day on average) had children 25% more likely to have higher developmental scores at 6 months and almost 30% more likely to have higher scores at 18 months.
Longer duration of breastfeeding was also associated with better infant development, especially at 18 months. Breastmilk also contains omega-3 fatty acids. The benefit of fish consumption was similar among infants breastfed for shorter or longer durations.
“In previous work in a population of U.S. women, we similarly found that higher prenatal fish consumption was associated with an overall benefit for child cognitive development, but that higher mercury levels attenuated this benefit,” says Dr. Oken. “Therefore, women should continue to eat fish—especially during pregnancy—but should choose fish types likely to be lower in mercury.” Information on mercury levels in commonly consumed fish is available at the U.S. Food and Drug Administration website.
Source: American Journal of Clinical Nutrition, September, 2008