Our sleep efficiency tends to decrease across our lifetime. In a recent study, researchers at the Medical College of Georgia were surprised to find sleep efficiency stabilized from ages 30 to 60.
True sleep time is difficult to measure, as most assessments are self-reports of sleep, explained study first author Dr. Shaoyong Su.
For the investigation, participants wore accelerometers on their wrist 24 hours a day for seven consecutive days. While the device does not measure sleep time, measuring movement can give some indication of whether you are asleep or not, noted study co-author Dr. Vaughn McCall.
“We confirmed previous findings based on subjective measurement,” said Dr. Su. “People think children and adolescents sleep later and we found this. And, during middle age people sleep less and our findings support that objectively.” He said that in addition, sleep duration is increased for those age 60 and older.
The researchers found that generally, nighttime sleep decreases as our age increases. However, the ‘U’ shape emerged as sleep duration dropped significantly from age 10 into the 50s, getting longer after that.
A graph of how long Americans sleep forms a U-shaped pattern across our lives, with age 40 being the low point and hours of sleep starting to creep back up about age 50. Increased sleep later in life may reflect that most Americans retire in their 60s and don’t get up as early.
Sleep efficiency – the time you actually sleep versus the time you have dedicated to sleep – also tends to decrease with age. The study found, however, that this was stabilized from ages 30 to 60. This indicates that adults maintain sleep efficiency for a long period, but may get the least sleep in their busy middle age.
Females were found to sleep longer than males but go to sleep later, particularly as they get older, and are interrupted by childcare duties.
The study showed that males and females were equally sleep efficient since females are more likely to report worse quality and more disturbances. While more study is needed to understand gender differences in sleep, these differences should be considered in treatment of sleep health.
Young American adults aged 20 had the latest clock time for sleep onset (CTSO), the time participants actually went to sleep. High school students had the biggest weekday/weekend differences between the time they went to sleep and awakened, which aligned with the school year.
For school-age children, the CTSO was 9:30 pm, while 25 percent of children ages 6 to 13 had a CTSO close to 11 pm. These patterns could reflect changes during adolescence, but could also be influenced by fatigue, behavioral problems and less academic success.
Moving into their 20s, a lot of people transition to work life and the CTSO begins to reverse. ‘’You hit the years where you are raising children and you are working and then what happens around the time of retirement? Your whole schedule begins to change,” said Dr. McCall, and the CTSO gets later again.
Black Americans tended to have some of the most troublesome sleep parameters, going to sleep later, sleeping less hours and less efficiently. Mexican Americans had the earliest sleep onset and longest sleep time but were not necessarily efficient sleepers. The findings point to the need for more research on racial disparities in sleep that take into account social and cultural factors.
“One thing we cannot overestimate is the impact of sleep,” noted Dr. Wang. Without sufficient sleep, you overuse your body, she said, and your ability to adjust to less sleep decreases with age.
While insufficient sleep itself is a risk factor of health problems from obesity to cardiovascular disease, it may also be an indicator of disease. How we sleep is like a “canary in a coal mine,” as sleep complaints may be an indication of mental or physical health problems.
“I don’t look at our findings necessarily as a benchmark of perfect health,” said Dr. McCall. “I look at this as a benchmark of what is happening in America.”
Our natural instincts are to go to sleep when it gets dark and wake up with the light, but life obligations interfere with our internal circadian clocks, the investigators explained. .
Babies’ sleep patterns tend to follow these more natural circadian rhythms, Su notes. The days before television, the internet and mobile phones, likely had more of us sleeping like babies, McCall says.
“Is it in the biology of a 20-year-old to always go to bed late or is it due to the fact that they have friends that they are engaged with and they have parties and college keg night? I think there is a lot of societal influence here,” said Dr. McCall. “Life gets in the way.”
The National Sleep Foundation says healthy adults need seven to nine hours of sleep, those over 65 need seven to eight hours and babies, young children and teens need more sleep than healthy adults to enable growth and development. Newborns, who rarely sleep through the night, need 14 to 17 hours including naps.
The research was supported by the National Institutes of Health and the American Heart Association and is published in the journal Scientific Reports.