The role of sleep changes with every stage of life, from infancy to old age. The latest neuroscience is discovering how crucial sleep is to an infant’s growing brain, while the latest epidemiology is discovering how irregular sleep doubles the risk of death as we grow older. To mark National Sleep Week, Thrive Global spoke with some of the top researchers in sleep science to give you a map of how sleep changes through your lifespan.
What scientists are discovering about sleep through the ages is fascinating, like how sleep helps the brain lay down the equivalent of fiber-optic cable before you’re even born to the way “social jet lag” affects the lives of primary schoolers to why you have trouble staying asleep as you get older.
With that said, let’s dive in.
Infancy: When sleep helps build your brain.
The need for and power of sleep starts showing up before you even properly enter the world. Beginning in the third trimester of pregnancy, a fetus starts exhibiting what looks like rapid eye movement (REM) sleep, which, in adults, is when dreaming occurs and memories are stored. For fetuses, neurons are growing rapidly — it’s like “an internet service provider laying down high-speed fiber optic cable within the brain,” says Matthew Walker, PhD, the principal investigator at the University of California, Berkeley’s Sleep and Neuroimaging Laboratory. Even before a baby is born, it already has circadian rhythms, or the “body clock” that determines your wakefulness and sleepiness throughout the day.
Once we’re out in the world, sleep becomes our primary activity. On average, a newborn infant sleeps 16–17 hours a day and a six-month-old sleeps 13–14 hours a day. In that first year of life, a baby spends more than half of its time sleeping. As Thrive Global founder and CEO Arianna Huffington notes in her book The Sleep Revolution, infants spend about half of their sleep in REM, a rate that falls to about 20 percent after their first birthday and stays stable into adulthood.