Diurnal variations in folacin levels of human milk: use of a single sample to represent folacin concentration in milk during a 24-h period.

Studies of breast-feeding and its adequacy for the infant could be simplified if a single milk sample were representative of nutrient levels during a 24-h period, despite diurnal variation. In this study, free and total folacin levels were measured in samples collected from 27 well-nourished mothers at each infant feeding from 2 wk to 1 yr of lactation. Folacin levels were higher (p less than 0.05) in the afternoon and evening than in the morning; variations decreased as lactation progressed (greater than 8 mo) and paralleled the decreased number of daily feedings. Despite 2- to 3-fold variations in milk folacin levels occur a 24-h period during the first 10 mo of lactation, the level in a single sample obtained at 1300-1450 h was representative (r = 0.74-0.93) of mean folacin concentration in samples obtained from all feedings during a 24-h period.