Circadian Variation in Human Milk Composition, a Systematic Review
What this study found
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;…
- Study & population
- 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.
- Key limitation
- 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.
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Open PDFOriginal 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 varies throughout the day. Circadian fluctuations in some bioactive components are suggested to transfer chronobiological information from mother to child to assist the development of the biological clock. This review aims to give a complete overview of studies examining human milk components found to exhibit circadian variation in their concentration. Methods: We included studies assessing the concentration of a specific human milk component more than once in 24 h. Study characteristics, including gestational age, lactational stage, sampling strategy, analytical method, and outcome were extracted. Methodological quality was graded using a modified Newcastle-Ottawa Scale (NOS). Results: A total of 83 reports assessing the circadian variation in the concentration of 71 human milk components were included. Heterogeneity among studies was high. The methodological quality varied widely. Significant circadian variation is found in tryptophan, fats, triacylglycerol, cholesterol, iron, melatonin, cortisol, and cortisone. This may play a role in the child’s growth and development in terms of the biological clock.