New research shows that the natural fatty acid composition of breast milk may play a key role in promoting better and longer sleep for infants, highlighting the impact of early nutrition on healthy development.
Study: Associations among human milk polyunsaturated fatty acids and infant sleep patterns: a cross-sectional study. Image Credit: PeopleImages.com - Yuri A / Shutterstock
In a recent study published in The Journal of Nutrition, researchers examined associations between polyunsaturated fatty acids (PUFAs) in human milk (HM) and sleep patterns among infants.
Infant sleep is a dynamic developmental process, entwined with body weight, cognition, and metabolism. Various studies underscore the importance of sleep for regulatory, physiological, and metabolic processes. Infants spend about 70% of their time sleeping in the first weeks of life, with evidence indicating lasting effects of sleep patterns on health outcomes.
Exclusive HM feeding is recommended for optimal infant development and growth for the first six months. Fats are a major macronutrient constituent in HM, with PUFAs representing one-fifth of total fats in HM. PUFAs are vital for key developmental processes, including central nervous system (CNS) maturation and retinal and brain function; PUFAs may also affect sleep regulation. Nevertheless, there is limited research on how HM PUFA content relates to sleep outcomes in exclusively HM-fed infants.
About the study
In the present study, researchers assessed associations between PUFAs in HM and sleep patterns in exclusively HM-fed infants. This study was a secondary analysis of data from a randomized controlled trial (RCT) assessing the efficacy of lactation cookies.
Female parents of exclusively HM-fed infants aged two months in the United States were eligible for inclusion if their infant was healthy and term-born from a healthy pregnancy and uncomplicated birth. Data were collected on sociodemographics, maternal pre-pregnancy height and weight, and infant birth weight and length.
Infant sleep data were obtained using the parent-reported brief infant sleep questionnaire. The study's primary outcome was an infant's total sleep time in 24 hours, estimated as the sum of total nocturnal and diurnal sleep time. Secondary outcomes included sleep latency and night wakings. Participants were asked to provide fasting milk samples for analysis.
Fatty acid methyl esters were extracted from samples and analyzed using gas chromatography-flame ionization. Multivariate linear regression models were used with infants' total 24-hour sleep time as the main outcome and night wakings and sleep latency as exploratory outcomes. Models were adjusted for pre-pregnancy body mass index (BMI), number of feedings, infant sex, and two-month weight-for-length z-scores.
Findings
The original trial included 176 participants; this sub-study included 131 individuals who provided a milk sample. The average infant age was 2.04 months at milk sample collection. Most participants had obesity or overweight before pregnancy (63.4%), a bachelor’s degree or higher (63%), and identified as White (81.7%). On average, the total 24-hour sleep was 14.6 hours, with infants sleeping for 6.22 hours during the day and 8.44 hours at night.
The average sleep latency was 43.8 minutes. PUFAs constituted 20.9% of total HM fatty acids. Omega-3 and omega-6 fatty acids represented 1.7% and 19.1% of fatty acids, respectively. Linoleic acid (LA) accounted for 17.7% of total HM fatty acids. Eicosapentaenoic acid, docosahexaenoic acid (mean 0.20%), arachidonic acid, and alpha-linolenic acid (ALA) constituted 0.06%, 0.20%, 0.45%, and 1.37%, respectively.
HM omega-3 and omega-6 fatty acids were significantly associated with total sleep duration. Among individual PUFAs, LA and ALA were significantly associated with total sleep duration. However, no significant associations were found for nocturnal sleep duration.
Higher proportions of HM PUFAs showed significant associations with diurnal sleep time rather than nocturnal sleep time. Similarly, among individual PUFAs, LA and ALA were positively associated with diurnal sleep.
Conclusions
Taken together, the findings revealed that a higher proportion of HM PUFAs relative to total HM fatty acids was associated with a clinically meaningful increment in infant sleep time.
In particular, each 1% increase in HM omega-3 fatty acids was associated with approximately 60 more minutes of sleep, while a 1% increase in omega-6 fatty acids correlated with about 8 additional minutes. However, the researchers noted that a 1% omega-3 increase represents a larger relative change (about two standard deviations) versus omega-6 (about 0.25 SD), cautioning against direct comparison of these values.
Notably, the increments in sleep related to PUFAs were exclusively observed during diurnal periods. Further, ALA showed significant associations with diurnal and total sleep, suggesting a potential role in sleep regulation via mechanisms discussed in the paper, such as circadian rhythm modulation or melatonin release.
The study’s limitations include its observational design, which precludes causal inference; possible recall bias due to caregiver-reported sleep data; and the lack of adjustment for multiple comparisons, which may increase false-positive risk.
Moreover, the study relied on fatty acid proportions rather than absolute concentrations, which only provide complementary insights. Further research is needed to corroborate these findings, delineate the underlying biological mechanisms, and examine the impact of maternal diet and lactation factors on infant sleep trajectories.