Comparing saliva and urine samples for measuring breast milk intake with the 2H oxide dose-to-mother technique among children 2–4 months old

Summary

Saliva and urine are the two main body fluids sampled when breastmilk intake is measured with the deuterium oxide dose-to-mother technique. However, these two body fluids may generate different estimates of breastmilk intake due to differences in isotope enrichment. Therefore, we aimed to assess how the estimated amount of breastmilk intake differs when based on saliva and urine samples and to explore whether the total energy expenditure of the mothers is related to breastmilk output. We used a convenience sample of 13 pairs of mothers and babies aged 2 to 4 months, who were exclusively breastfed and apparently healthy. To assess breastmilk intake, we administered doubly labelled water to the mothers, and collected saliva samples from them, while simultaneously collecting both saliva and urine from their babies over a 14-day period. IRMS was used to analyze the samples for deuterium and oxygen-18 enrichments. Mean breastmilk intake based on saliva samples was significantly higher than that based on urine samples (854.5g/day vs. 812.8g/day, p=0.029). This can be attributed to slightly higher isotope enrichments in saliva and to a poorer model fit for urine samples as indicated by a higher square root of the mean square error (14.6 vs. 10.4 mg/kg, p=0.001). Maternal energy expenditure was not correlated with breastmilk output. Our study suggests that saliva sampling generates slightly higher estimates of breastmilk intake and is more precise as compared to urine and that maternal energy expenditure does not influence breastmilk output