Study: Babies grow most when they sleep the most

Babies do sprout up overnight, it turns out. Researchers looking at infant sleep have shown that babies sleep more and longer just when growth spurts hit. This might give parents some comfort, because the findings also account for the irregular sleep that so confounds moms and dads of growing infants.

"Sleep irregularities can be distressing to parents," Michelle Lampl, of Emory University/Georgia Tech's Predictive Health Institute, said in a release. "These findings give babies a voice that helps parents understand them and show that seemingly erratic sleep behavior is a normal part of development. Babies really aren't trying to be difficult." Lampl is lead author on the study, which appears in this week's edition of the journal Sleep.

Boys and girls also go about growth spurts differently, the researchers found. Boys tend to sleep longer when they're undergoing rapid growth while girls tend to have more bouts of sleep.

Neither the sex of the infant nor breastfeeding had significant effects on total daily sleep time. But breastfed infants had more but shorter bouts of sleep.

The study was based on data from 23 infants recorded in real time over a four- to 17-month span, using daily diaries kept by their mothers.