Urinary lactose: changes postpartum and relation with breast milk production

Abstract

Measurement of milk intake by breast-fed infants is difficult and a simple measure would be helpful for research and clinical practice. Maternal urinary lactose excretion has been proposed as a simple measure of lactation performance. The objectives of this study were to describe the pattern of urinary lactose excretion postpartum, and to determine whether lactose excretion could predict breast milk output. Lactose excretion was determined in 50 lactating and 49 nonlactating women at 0.5, 3, and 6 mo postpartum, and in 29 weaning women and 30 nonlactating women at 5, 8, and 11 mo postpartum. Lactose excretion was 4- to 17-fold higher in lactating than in nonlactating women, depending on the time point studied, and was highest in both groups 0.5 mo postpartum. Lactose excretion decreased after weaning but remained higher than in nonlactating women 1.3 mo after weaning was completed. Sixty-two additional women between 1.5 and 12 mo postpartum were studied to determine the ability of urinary lactose to predict milk output. There was a positive association between milk output and urinary lactose excretion, with correlation coefficients ranging from 0.17 to 0.30 depending on the measurement interval for lactose excretion. Lactose excretion could explain 2-9% of the variance in milk output, and could correctly classify 29-40% of individuals into tertiles of milk output. Although urinary lactose excretion reflects changes in biological activity of the mammary gland and gross changes in milk production, it is not a precise predictor of milk output.