Not getting enough sleep? Experts say turn off the smartphone late at night

If you think you’ve been getting less sleep the past several years, you’re not alone.

A recently released study finds that the percentage of Americans getting six hours of sleep or less each night has been rising. A leading culprit may be in your hand: smartphones and other electronic devices that many look at in bed.

Many people likely will get even less sleep than usual over the next few days, as they adjust to clocks springing forward at 2 a.m. Sunday for daylight saving time.

The study, by researchers from Arizona State University, the University of Southern California and the University of South Carolina, found that 33 percent of Americans reported getting six hours or less of sleep in 2017 — up from 29 percent in 2012. The findings appear in the February issue of the journal “Sleep.”

Experts say adults 18 to 60 years old should get at least seven hours of sleep per night, with more shut-eye recommended for children and older adults, according to the U.S. Centers for Disease Control and Prevention.

Connor Sheehan, the study’s lead author and an assistant professor of social and family dynamics at Arizona State, noted that the increase in “short sleep” — six hours or less — tracked with a sharp rise in smartphone use.

“If you’re bringing a really bright light into bed and holding a bright light close to your face, and consuming stressful tweets or news or emails from work, or texts from family, that’s not great for your sleep,” he said.

The percentage of Americans owning smartphones rose from 39 percent in 2012 to 77 percent in 2018, according to the Pew Research Center.

Exposure to the light from smartphones can suppress the release of sleep-inducing melatonin and increase alertness, studies have found.

The sleep-duration study was based on the responses of nearly 400,000 adults who participated in the federal government’s National Health Interview Survey from 2004 to 2017. The study found that the prevalence of short sleep was relatively stable between 2004 and 2012, including during the 2007-09 recession.

The recession may have led to less sleep for people worried about losing their jobs or homes, said Jennifer Ailshire, an assistant professor of gerontology and sociology at USC and senior author of the study. But it also may have led to more sleep for some people, including those without jobs. The two groups may have “canceled each other out,” she said.

Ailshire said that even though the unemployment rate since has fallen, many people have contract positions or freelance work that involve more uncertainty and stress. In addition, with smartphones, many employees — especially younger workers — can get stressful emails at any hour.

“The reality, especially for younger workers who don’t have the same level of job stability, is you can’t ignore those emails — or you don’t think you can,” she said.

The study found a larger increase in short sleep among African-Americans and Latinos than whites. The percentage of black respondents reporting short sleep rose from 35 percent in 2004 to 42 percent in 2016, before dropping slightly in 2017. The proportion of Hispanics with short sleep increased from 26 percent in 2004 to 33 percent in 2017. Short sleep among whites rose from 29 to 31 percent during that time.

One reason for the racial gap could be because the recession and its aftereffects impacted African-Americans and Latinos more severely, Sheehan said. Other factors could include increased coverage of police violence against African-Americans, and increased deportations, he said.

Although the study found an increase in short sleep, another sleep-duration study, also published in “Sleep,” in April 2018, came to an opposite conclusion. That study, from researchers at the University of Pennsylvania, was based on more than 181,000 people who participated in the federally sponsored American Time Use Survey, which asks how long respondents spend on various activities. It found a decrease in the number of people getting seven hours sleep a night or less.

Lauren Hale, a professor of family population and preventive medicine at Stony Brook University’s Renaissance School of Medicine, said both studies have limitations because they rely on self-reporting.

“People are not good judges of when they are sleep,” said Hale, founding editor-in-chief of the Sleep Health Journal.

The time-use survey is especially prone to overestimating sleep time because some actions deemed “sleep” — such as “falling asleep” and “waking up” — may not involve actual sleep, she said. Some respondents may count winding-down bedtime activity — such as chatting with a spouse while in bed — as sleep.

Hale said research involving movement-detecting devices worn on the wrist can provide more reliable approximations of sleep time. Between 2014 and 2016, Hale and researchers from three other universities measured the sleep of more than 800 teenagers using the devices and have applied for funding to measure the same people again, to determine whether sleep duration increased, decreased or was stable as they enter young adulthood. It may be the first national longitudinal study of sleep using the devices, she said.

Sheehan said racial disparities in short sleep could widen the existing disparities in the overall healthiness of whites, African-Americans and Latinos.

Studies show that insufficient sleep can lead to an array of health problems, including hypertension, obesity and diabetes, said Dr. Harly Greenberg, medical director of the Northwell Health Sleep Disorders Center at North Shore University Hospital in Manhasset.

“You need to rev up your alerting systems, your arousal systems, to compensate and maintain wakefulness in the face of insufficient sleep time,” he said.

That can raise the heart rate, increase blood pressure and constrict blood vessels, he said.

Lack of sleep also appears to affect mechanisms in the brain that regulate appetite, leading to a greater craving for high-calorie foods, including sweets, Greenberg said. That can lead to weight gain.

In addition, sleep deprivation makes tissues in the body more resistant to the effect the hormone insulin has in facilitating the transfer of glucose from the bloodstream to tissues — leading to higher levels of glucose in the blood, he said. That may increase the risk of diabetes.