Getting the recommended seven to eight hours of sleep every night is a struggle for most people, but even those who do may not have the best sleep.New research from Iowa State University finds more Americans have trouble falling asleep and staying asleep. The changes were independent of sleep duration, and difficulties were most prevalent in people with healthy sleep length, the findings show. The study, published in the journal Sleep Health, is one of the first to look at how multiple dimensions of sleep health change over time.

Zlatan Krizan, professor of psychology, and his research team analyzed data collected from nearly 165,000 individuals from 2013 to 2017, as part of the National Health Interview Survey. Over the course of five years, adults who reported at least one day a week with difficulty falling asleep increased by 1.43% and those reporting at least one day with trouble staying asleep increased by 2.70%. While the percentages may seem small, Krizan says based on 2018 population estimates this means as many as five million more Americans are experiencing some sleep difficulties.

"Indeed, how long we sleep is important, but how well we sleep and how we feel about our sleep is important in its own right," Krizan said. "Sleep health is a multidimensional phenomenon, so examining all the aspects of sleep is crucial for future research."

What's causing the problems?

Based on the National Health Interview Survey data, ISU researchers cannot say what is contributing to the worsening of sleep quality. However, Garrett Hisler, lead author and former Iowa State graduate student who is now a postdoctoral researcher at the University of Pittsburgh, says technology is likely a factor.

"We know from our previous research there is a correlation between smartphone use and insufficient sleep among teens," Hisler said. "If we're on our phone before bed or we're receiving alerts in the middle of the night that can make it harder to fall asleep and stay asleep throughout the night."

Consistent with other studies, ISU researchers found the average time spent sleeping decreased. Although the number of people who reported waking up and feeling rested also increased, Krizan says this spike was only observed for one year and is less representative of a trend.

Sleep linked to health

By taking a broader look at sleep quality, researchers aim to better understand the link between sleep and health outcomes. In the paper, they explain that sleep duration combined with poor sleep quality can increase the risk for cardiovascular disease, and sleep quality can affect our overall wellbeing.

"We know that how well people sleep is generally very reflective of people's health and may be an indicator of other conditions," Krizan said. "If we want a full picture of the population's health, it's important to measure and track these changes in sleep trends over time."

Krizan says the findings suggest that intervention efforts might be more effective by targeting factors that influence the initiation and maintenance of sleep as well as the length of sleep. More research is needed to identify how changes in sleep duration and other sleep characteristics are related.