Circadian Variation in Human Milk Composition, a Systematic Review

Nutrients
Q1
Aug 2020
Citations:126
Influential Citations:8
Systematic Reviews / Meta-Analyses
86
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Enhanced Details

Methods
Observational studies; cross-sectional and longitudinal designs; 83 studies included; participants were lactating mothers; age range 13-53 years; mostly term deliveries; lactational stage ranged from colostrum to mature milk; sampling frequency ranged from 2 to 12 times per 24 h; observation duration 1-14 days.
Results
Strong evidence of circadian variation in tryptophan, fats, triacylglycerol, cholesterol, iron, melatonin, cortisol, and cortisone in human milk; carbohydrate and total protein show no consistent circadian variation. Some amino acids (e.g., tryptophan) may vary; fat-related lipids tend to peak in the evening; iron peaks in the evening/night; melatonin peaks at night; cortisol and cortisone peak in the morning. Evidence for many other components is inconclusive due to limited data and heterogeneity. These rhythms may provide circadian cues to the infant and support circadian development; mismatches between milk expression timing and feeding could disrupt clock entrainment. Meta-analysis could not be performed due to heterogeneity. Recommendations include four or more time points per 24 h for milk sampling and adjusting analyses for milk-expression timing; further research should link rhythms to child health outcomes.
Limitations
High heterogeneity across studies; small and varied sample sizes; short observation windows (often one day); variable sampling frequencies; limited data for many components; potential confounders (maternal factors, lactation stage, mode of delivery) not consistently accounted for; limited generalizability.

Abstract

Background: Breastfeeding is considered the most optimal mode of feeding for neonates and mothers. Human milk changes over the course of lactation in order to perfectly suit the infant’s nutritional and immunological needs. Its composition also varie...