LAUSR

In early childhood, irregular sleep schedules that may promote circadian rhythm misalignment predict greater weight gain. However, circadian rest-activity (CRA) rhythmicity in infancy in relation to growth is understudied. The aim of the present study was to investigate the association between newborn circadian rest-activity rhythmicity and change in weight-for-age from birth to three months. Data were captured as a secondary data analysis from the Snuggle Bug / Acurrucadito Study (see Support). English or Spanish speaking mothers (n=41, age M±SD=33.1±4.6y, 31.7% Hispanic/Latina) and their full-term (≥37wk) infants of normal weight (2.5-4kg; 58.5% female; 25.6% WIC enrolled) were recruited from Phoenix, Arizona. CRA rhythmicity was measured at eight weeks with ankle-worn Micro Motionloggers (Ambulatory Monitoring Inc.) for five 24hr periods at one-minute epochs. CRA metrics assessed included 24hr autocorrelation, mesor, magnitude, acrophase, goodness-of-fit R2, interdaily stability, intradaily variability, and relative amplitude. Birthweight was mother-reported and 3mon infant weight was measured with a Seca scale. Weight-for-age Z-scores (WAZ) by infant sex were computed based upon World Health Organization growth charts and the change difference between timepoints was the primary outcome. Regression models adjusting for birth WAZ examined the relationships between CRA metrics at eight weeks with change in WAZ from birth to 3mo. At eight weeks, mean±SD CRA metrics were as follows: 24hr autocorrelation of 0.25±0.03, mesor of 115.6±14.7, amplitude of 68.1±18.3, goodness-of-fit R2 of 0.42±0.10, acrophase of 14:12±1:42, interdaily stability of 0.57±0.12, intradaily variability of 0.93±0.19, and relative amplitude of 0.61±0.11. Mean birth WAZ and change in WAZ from birth to 3mon were 0.39±0.73 and -0.57±0.77, respectively. After adjusting for birth WAZ, in separate models, greater mesor (R2 Change=0.10, β=-0.32, p=0.03), amplitude (R2 Change=0.11, β=-0.34, p=0.03), and goodness-of-fit R2 (R2 Change=0.10, β=-0.32, p=0.04) were significantly associated with less change in WAZ from birth to 3mon. Among relatively healthy, full-term infants born of normal weight, greater 24hr circadian rest-activity rhythmicity achieved by 8 weeks was associated with slower rate of weight gain across the newborn stage. Promoting behaviors and environmental cues from parents that strengthen early circadian rhythmicity in their infants may promote healthy weight trajectories. NIH/NHLBI R01HL147931