Naptime! A new study released this week has identified growth spurts in babies are related to more frequent bursts of sleep. 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. Further analysis found that the probability of a growth spurt increased by a median of 43% for each additional sleep episode and 20 percent for each additional hour of sleep.
For a duration ranging from four to 17 continuous months, growth in total body length was assessed using the maximum stretch technique, which was performed semi-weekly for 18 infants, daily for three infants and weekly for two infants.
Researchers at Emory University in Atlanta stated:
“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. On a practical, everyday level, it helps parents understand their infant’s behavior and patterns. It opens another door to understanding why we sleep. We now know that sleep is a contributing factor to growth spurts at the biological level.”
The exact nature of the relationship between sleep biology and bone growth is unclear. However, researchers noted that the secretion of growth hormone is known to increase after sleep onset and during the stage of slow wave sleep. This change in hormonal signals during sleep could stimulate bone growth, which would support anecdotal reports of “growing pains,” the aching limbs that can wake children at night.
The report speculates that in some cases growth may have occurred in other parts of the body. For example, another new study they are publishing this month found that infant head circumference grows in intermittent, episodic spurts. They also suggest that sleep may be only one component of an integrated, physiological system that underlies growth timing.
Over a typical lifespan, the amount of time we spend each day sleeping declines. Newborns spend from 16 to 20 hours asleep each day. Between the ages of one and four, total daily sleep time decreases to about 11 or 12 hours. This gradual decline continues through childhood, such that an adolescent will need – though not necessarily get – about nine hours of sleep to function at his or her best. Adults through middle age need at least eight hours, and although the elderly may still require up to eight hours, they may struggle to obtain those hours in one block.
Our bodies require sleep in order to maintain proper function and health. In fact, we are programmed to sleep each night as a means of restoring our bodies and minds. Two interacting system, the internal biological clock and the sleep-wake homeostat, largely determine the timing of our transitions from wakefulness to sleep and vice versa. These two factors also explain why, under normal conditions, we typically stay awake during the day and sleep at night.
Afternoon naps for most people typically last between 30 and 60 minutes. Any longer and there is a risk of falling into deep sleep and having a difficult time waking. Following a nap, having dissipated some of the accumulated sleep drive, many people report feeling better able to stay awake and alert in the late afternoon and evening. This increased alertness typically causes people to go to bed later and generally to sleep less at night than people who do not take naps.
Written by Sy Kraft