Nutritional composition of a mother’s breast milk may depend not just on her diet - but on her genes

The nutritional composition of a mother’s breast milk may depend not just on her diet - but on her genes - according to new research at Wake Forest University Baptist Medical Center.

“It is well known that genes control the nutrient levels in cow’s milk” said Richard B. Weinberg, M.D. “But until now, no one has considered how genes might affect human breast milk. This is the first study to demonstrate a genetic effect on human lactation.” The results were presented today at Digestive Disease Week 2005 in Chicago, Ill.

The research study looked at how much of an omega-3 fat called docosahexaenoic acid (DHA) gets from a mother’s diet into her breast milk. DHA, which is found mainly in cold-water fish such as tuna, salmon, and mackerel, is essential for healthy brain and eye development. DHA is now added to several brands of infant formula because of research showing its beneficial effects.

One study, for example, found that premature babies who got DHA supplements had better vision and reached development milestones earlier than infants who didn’t get the supplements. On the other hand, insufficient DHA has been implicated in developmental disorders such as autism, attention deficit hyperactivity disorder, and learning disabilities, Weinberg said.

“Until now, we’ve assumed that women consuming an equal amount of DHA in their diets would have the same amount in their breast milk,” said Weinberg, a professor of gastroenterology and nutrition researcher at Wake Forest University School of Medicine. "But we found that women with a common genetic variant produced milk containing higher levels of DHA.”

In the study, 111 women ate a meal with an added dose of DHA and then pumped their breast milk hourly for 12 hours. The researchers then analyzed the amount of DHA and other fats in their blood and breast milk, and determined which women carried variants of ApoA4, a gene involved in dietary fat absorption. The results showed that women who carried the 347S variant, which is present in about one-third of the U.S. population, had 40 percent more DHA in their breast milk than women who had the more common (347T) version of the gene.

“These women were more successful at getting the DHA they had just eaten into their bloodstreams and then into their breast milk,” said Weinberg.

The researchers also observed a significant impact of the E4 variant of ApoE , a gene that regulates fat metabolism in the bloodstream. The E4 variant, which is present in about 20 percent of the U.S. population, is associated with an increased risk for both heart disease and Alzheimer's disease. They found that mothers who carried either one or two copies of the E4 variant had 40 to 75 percent less total fat in their breast milk compared to women who did not have the variant.

"This unexpected finding suggests that the E4 variant could affect the total amount of calories that a mother can provide to her infant in her milk,” said Weinberg.

Weinberg cautioned that much more research is needed before these findings can be translated into nutritional recommendations for pregnant and nursing women. He predicted, however, that in the future, similar genetic testing may help identify women who need to modify their diet or take supplements to maximize the nutritional value of their breast milk.

An expanded study is planned to examine the clinical impact of additional genes and their effects on prenatal storage of DHA and other omega-3 fatty acids in body fat.

The research was funded by the National Institute of Diabetes and Digestive and Kidney Diseases and was conducted in Wake Forest Baptist’s National Institutes of Health funded General Clinical Research Center. Co-investigators are Amanda T. Greenwood, B.A., and Raquel Chacon-Angobaldo, B.A., both with Wake Forest.