New research provides evidence for something parents have long suspected-babies grow during sleep. The study, published in Sleep, found that in infants, growth in length follows prolonged sleep and increased naps.
To determine whether changes in daily infant sleep patterns were temporally related to growth spurts in total body length, researchers asked parents to keep daily records of their infants’ sleep patterns (ie, number of sleep bouts, hours per sleep bout, and total sleep hours). Twenty-three parents of healthy infants maintained daily records over 4 to 17 months (5,798 daily records), starting at a median age of 12 days.
Significant within- and between-infant variability in sleep hours, number of sleep bouts, and hours per bout were noted; breastfeeding and sex of the infant accounted for 44% of the variances in sleep bouts.
The sleep diaries showed that saltatory (episodic) growth in infant length was significantly associated with both increased total hours of sleep and number of sleep bouts. Among boys, growth spurts were associated with an increased duration of sleep bouts, whereas among girls, growth spurts were associated with an increased number of sleep bouts.
The average duration of peaks in total daily sleep hours was 2 days, with an average increase of 4.5 hours per day and/or 3 or more naps per day.
Significant differences between infants were observed in the relationship between sleep and growth. In 12 infants, each additional sleep bout increased the probability of a spurt in length growth by a median of 43%; in 8 infants, each additional hour of sleep increased the probability of length growth by 20%.
Increased duration of sleep bouts was significantly associated with greater weekly weight gain and accrual of abdominal skinfolds as well as truncal adiposity.
The researchers note that this was the first study to document that episodic growth in length in infants is related to changes in sleep. The findings, researchers say, suggest that sleep is integrating multiple anabolic processes in normal growth and development.
Lampl M, Johnson ML. Infant growth in length follows prolonged sleep and increased naps. Sleep. 2011;34(5):641-650.