Abstract
Saliva and urine are the two main body fluids sampled when breast milk intake is measured with the 2H oxide dose-to-mother technique. However, these two body fluids may generate different estimates of breast milk intake due to differences in isotope enrichment. Therefore, we aimed to assess how the estimated amount of breast milk intake differs when based on saliva and urine samples and to explore whether the total energy expenditure of the mothers is related to breast milk output. We used a convenience sample of thirteen pairs of mothers and babies aged 2-4 months, who were exclusively breastfed and apparently healthy. To assess breast milk 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-d period. Isotope ratio MS was used to analyse the samples for 2H and 18O enrichments. Mean breast milk intake based on saliva samples was significantly higher than that based on urine samples (854·5 v. 812·8 g/d, 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 v. 10·4 mg/kg, P = 0·001). Maternal energy expenditure was not correlated with breast milk output. Our study suggests that saliva sampling generates slightly higher estimates of breast milk intake and is more precise as compared with urine and that maternal energy expenditure does not influence breast milk output.
Highlights
The WHO recommends to exclusively breastfeed children during the first 6 months of life[1]
In studies with labelled water, the level of isotope enrichment has been found to differ between types of body fluids, with saliva samples having a slightly higher isotopic enrichment than urine samples[12,13,14,15]
Jankowski et al and Schierbeek et al found that, as opposed to urine, saliva provides a more accurate estimate of the intended outcome[12,13]. Both saliva and urine have been sampled in studies to measure breast milk intake with the 2H oxide dose-to-mother technique[6,17,18,19], it is not known how the type of body fluid affects the estimate for breast milk intake
Summary
The WHO recommends to exclusively breastfeed children during the first 6 months of life[1]. The prevalence of exclusive breast-feeding is usually based on maternal recalls, which are often associated with recall bias and socially desirable responses that lead to over-estimation of the true prevalence[9] To overcome these challenges, a more objective technique called the ‘2H oxide dose-to-mother technique’ involving the use of stable isotopes was developed[8,10]. Jankowski et al and Schierbeek et al found that, as opposed to urine, saliva provides a more accurate estimate of the intended outcome[12,13] Both saliva and urine have been sampled in studies to measure breast milk intake with the 2H oxide dose-to-mother technique[6,17,18,19], it is not known how the type of body fluid affects the estimate for breast milk intake. Since we expected large differences in physical activity patterns between mothers, we simultaneously measured maternal energy expenditure by using doubly labelled water and explored how this was related to breast milk output
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