Do Sleepy Babies Grow More? The Science of Growth Spurts

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If you’ve ever been frustrated by your baby’s irregular sleep patterns, take heart. A new study suggests that erratic bursts of sleep may correspond to growth spurts.

The study’s lead author, Michelle Lampl, professor of anthropology at Emory University, and colleagues asked 23 sets of parents to keep daily sleep logs of their newborns (average age 12 days) for four to 17 months. They detailed their children’s sleep onset and waking patterns, as well as whether they were breast-fed or formula-fed, and whether they ever developed signs of illness like vomiting, rash, fever and diarrhea.

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The researchers measured the infants’ length often — anywhere from daily to twice a week — and cross-referenced their growth with parents’ sleep records.

They found that when babies’ sleep patterns shifted — when the infants began taking more naps or slept more overall — it was typically followed by a growth spurt. Specifically, babies were 43% more likely to experience a growth spurt for each additional nap they took, and 20% more likely to grow for each additional hour of sleep they got during these sleep peaks.

On average, babies’ growth-associated sleep patterns resulted in about 4.5 hours more sleep per day over two days, and three extra naps.

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Not only did the babies get longer when they slept more, they also got heavier — particularly gaining fat around the abdomen. “The results demonstrate empirically that growth spurts not only occur during sleep but are significantly influenced by sleep,” said Lampl in a statement.

Baby boys tended to nap more frequently than girls, but slept for shorter bursts, the researchers found. And breast-fed babies also took more frequent, shorter naps than formula-fed infants.

The association wasn’t perfect — not every shift in sleep pattern was associated with a growth spurt, and vice versa — but it was significant. The finding should help ease some parents’ anxiety about their infants’ problematic sleep. “Sleep irregularities can be distressing to parents,” said Lampl. “However, 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.”

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Although the study did not elucidate exactly how sleep affects growth — the authors theorized that changes in hormonal signals during sleep may boost the secretion of growth hormones — it adds to the evidence that sleep carries important biological functions.

The study was published in the May issue of Sleep.