To analyze the relation between sleep and growth of infants, the researchers did not rely on parent provided sleep pattern and growth. Instead, they recorded real time data spanning 4 to 17 months. There were 23 parents involved in the study, and 5,798 daily recordings were analyzed. Among the infants 14 were girls and 9 were boys with a median age of 12 days. All these babies were healthy, with no colic problems or any other medical complications.
Mothers involved in the research were asked to keep a daily diary that recorded the baby’s sleep schedule . They were also asked to note whether the baby was formula fed, breastfed or both. If the infant showed signs of illness like fever, rashes, diarrhea or vomiting, these were recorded too.
The growth in these babies was recorded using the maximum stretch technique. The recordings were done semi-weekly for 18 babies, weekly for two and daily for 3 babies.
The results showed that most of the infants slept irregularly with small bursts of sleep. In a 24-hour period the sleep duration increased at irregular intervals by an average of 4.5 hours a day for two days. They also found that per day the sleep duration increased in intermittent bursts with an average of three extra naps per day every two days.
These increased sleep periods were usually associated with growth bursts as well.
“These peaks in total daily sleep duration and number of sleep episodes were significantly associated with measurable growth spurts in body length, which tended to occur within 48 hours of the recorded bursts of sleep,” the study says.
With every additional nap time the baby had the growth spurt median increased by 43 percent. Also with every extra hour of sleep, there was a median 29 percent growth spurt increase.
According to lead researcher Dr. Michelle Lampl, Samuel Candler Dobbs Professor in the department of anthropology at Emory University in Atlanta, Ga. and co-author Michael Johnson, PhD, professor of pharmacology in the University of Virginia Health System this means that growth not only takes place during sleep, the amount of growth is also influenced by the duration of sleep.
“The results demonstrate empirically that growth spurts not only occur during sleep but are significantly influenced by sleep. Longer sleep corresponds with greater growth in body length.” he says.
The study also revealed that the gender of the baby influenced the amount of growth.Boys in general had more sleep bouts but of shorter duration than girls.
“Growth spurts were associated with increased sleep bout duration in boys compared with girls and increased number of sleep bouts in girls compared with boys,” says Lampl.
The study also found that compared to formula feeding, breast feeding led to more frequent and shorter sleep durations. It was also seen that some sleep bursts were not associated with growth and some growth spurts were not associated with sleep.
“Sleep irregularities can be distressing to parents,” says 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.”
The scientists still do not know the exact relation between sleep and growth, but have at least found out that growth hormones are triggered during sleep and during slow wave sleep and influence the bone growth of the baby.
The often quoted ‘growing pains’ that infants are said to have that wakes them from sleep at night, may also be explained this way.
In another research soon to be published it has been found that infant head circumference grows in intermittent, episodic spurts, suggesting that sleep may be only one component of an integrated, physiological system that underlies growth timing.
Thus, while the relation between sleep and growth has now been found out, there are other complex physiological occurrences too happening in the body that affect the growth of the baby.
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