Age, gender affect sleep, study finds

What constitutes a “normal” night’s sleep?

That all depends, says Danny Forger, a biological mathematician at the University of Michigan and an expert in circadian clocks.

“People set guidelines all the time — you need eight hours, you need seven hours — but we’ve found that ‘normal’ sleep varies tremendously depending on your age, sex and what country you are in,” he said.

Forger is the senior author of a new study that analyzed the sleep habits of more than 5,000 users of a mobile phone app known as ENTRAIN.

The free app was designed by Olivia Walch, a graduate student in Forger’s group. It was launched in 2014 to help users efficiently overcome jet lag with the help of a complex algorithm based on Forger’s previous research. Essentially, the app tells people when to expose themselves to light and when to avoid it to minimize the effects of jet lag.

Entrainment is the scientific term for fully adjusting to a new time zone — hence the app’s name. Most sleep 7-8 hours

The group also invited users to send the sleep data they plugged into the app back to the servers at the university. Roughly 8 percent of the app’s international users agreed to share their information anonymously, providing the team a treasure trove of real-world sleep statistics.

In a paper published Friday in Science Advances, Forger and his coauthors used the data they collected from ENTRAIN to provide an overview of the social and solar cues that influence when we go to sleep and when we wake up

Most people in the data set schedule between seven and eight hours of sleep a night, with a mean of 7.88 hours. Sensitive to solar cues

Of all the factors considered in their analysis, gender plays the biggest role in how long a person sleeps. On average, women schedule 8.07 hours of sleep, while men schedule 7.77 hours. Women both go to bed a bit earlier than men and wake up a bit later. The authors say this effect is most pronounced among people 30 to 60.

Age also seems to be an important factor for when people sleep. On average, older people schedule sleep earlier than younger people. Also, there is less variation in the times that older people sleep than younger people. The authors think this could be because older people are more sensitive to solar cues.