Researchers found low zinc levels in breast milk could be caused by a common genetic mutation
Zinc levels in breast milk may determine breast function during lactation, according to a new Penn State report.
In earlier research, Shannon L. Kelleher and colleagues found the protein ZnT2 is critical for secreting zinc into breast milk, and women who have mutations in the gene that encodes ZnT2 have substantially lower milk zinc levels, leading to severe zinc deficiency in babies who are breastfed exclusively.
In the current study, researchers have found the genetic variation that causes loss of function may be common in women and, in some cases, is associated with poor breast function. They suggest that identifying women with abnormally low levels of zinc in their breast milk may aid in recognizing moms who might have trouble breastfeeding.
For the study, researchers looked at 54 breastfeeding women and found that 36 percent had at least one mutation in the protein ZnT2, and that mutation was associated with abnormal levels of zinc in their breast milk. Twelve previously unknown variants of ZnT2 were identified in the participants, and five of these variants were associated with abnormal zinc levels in breast milk.
“We had no idea that genetic variation in ZnT2 would be so common,” said Kelleher, associate professor of cellular and molecular physiology and pharmacology in the Penn State College of Medicine.
The protein ZnT2 transports zinc in specific tissues of the body, including the mammary glands. Women who have mutations in ZnT2 may have difficulty breastfeeding because zinc is necessary for the growth of mammary glands and the function of mammary epithelial cells and secretion pathways.
Even if they are able to breastfeed successfully, their breast milk will likely contain a lower than normal amount of zinc, which can cause severe zinc deficiency in exclusively breast-fed infants. Infants who don’t receive enough zinc in their diet are in danger of immune system and developmental problems.
“Among the subjects with ‘normal’ milk (zinc levels), no variants in ZnT2 were detected,” the researchers said.
Though more research is needed to better understand how genetic variation affects milk zinc levels and breast function, the study findings are an important step in identifying breastfed infants who are at risk for zinc deficiency before they become deficient, as well as identifying women who might have trouble breastfeeding.