Measuring zinc levels in breast milk could help identify women who may have trouble breastfeeding, according to new research published in the Journal of Mammary Gland Biology and Neoplasia. Researchers at the Penn State University found that women with abnormally low levels of zinc in their breast milk may be an indicator of poor breast function during lactation.

Previous studies conducted by the same group of researchers have found that the protein ZnT2 is essential for regulating zinc in breast milk. Women who have mutations in the gene responsible for producing this protein tend to have significantly lower levels of zinc in their breast milk, which could lead to severe zinc deficiency in infants who are exclusively breastfed. The current study finds, too, that this genetic variation is common in women and can be associated with indicators of poor breast function.

Zinc is an essential mineral for the growth of mammary glands, as well as normal growth and development during pregnancy, childhood, and adolescence, The National Institutes of Health (NIH) reported. Even if women with genetic variations of the protein ZnT2 are able to breastfeed, their milk will likely contain a lower amount of zinc.

So in the new study, researchers collected and analyzed data from 54 breastfeeding women; 36 percent had at least one mutation in the protein ZnT2. Researchers also discovered 12 previously unknown genetic variants of ZnT2 in the participants, five of which were statistically associated with abnormal zinc levels in breast milk. The most comment ZnT2 variant, T288S, was found in 12 percent of breastfeeding women.

"We had no idea that genetic variation in ZnT2 would be so common," researcher Shannon Kelleher, associate professor of cellular and molecular physiology and pharmacology, said in a statement.

The participants were divided into four groups, according to breast milk zinc levels — from low to high. Investigators identified ZnT2 variants in 79 percent of the women in the group with the lowest levels of zinc, while only 29 percent of women had ZnT2 in the group with the highest levels. The breastfeeding women who had at least one genetic variant in ZnT2 had an abnormally low or high level of zinc in their breast milk.

"Importantly, among the subjects with 'normal' milk (zinc levels), no variants in ZnT2 were detected," the researchers wrote in the study.

Furthermore, after looking at the participant's ratio of sodium to potassium (Na/K) in the milk, which are indicators of breast dysfunction, including infection and inflammation of the breast, they found that women with the genetic variant T2885 had a significantly higher Na/K ratio than those who had no variation of ZnT2.

Although more research is needed to better understand how genetic mutation affects zinc levels in breast milk and otherwise breast function, the findings are an important step in identifying breast-fed infants who are at risk for zinc deficiency.

Source: Alam S, Hennigar S, Gallagher C, Soybel D, Kelleher S. Exome Sequencing of SLC30A2 Identifies Novel Loss- And Gain-of-Function Variants Associated With Breast Dysfunction. Journal of Mammary Gland Biology And Neoplasia. 2015