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A new study published in Scientific Reports looked at the epidemiology of accelerometer-based sleep parameters in US school-aged children and adults.

“The study is about the age, gender and racial distribution of objectively measured sleep parameters in the US population,” study author William V. McCall told us. “We are hoping to provide statistics on when people sleep, how long they sleep and their sleep efficiency in different age, sex and racial groups from a sample representative of American populations.”

According to statistics posted on the Sleep Foundation website, in the US, over thirty-five per cent of adults say they sleep less than seven hours per night. Adults aged 18-64 need an average of seven to nine hours of sleep nightly. That need slightly changes in adults over 65 who need seven to eight hours of sleep per night. In a survey of adults living in the US, nearly half say they feel sleepy during the day between three and seven days per week. 

The research team was foremost interested in the timing of sleep, and suspected that sleep onset times got later from pre-pubertal children through college years. They wanted to know what our sleep behaviors look like in the current model lifestyle (i.e. 24-hour, seven days) because adequate sleep is such an important contributor to our overall health and wellbeing.

“We calculated sleep parameters from the 24-hour actigraph data which was collected from a nationally representative sample,” McCall told us. “This is the first time 24-hour actigraph data were collected from a nationally representative sample.”

According to the Centers for Disease Control and Prevention, short sleep duration occurs when adults receive less than seven hours of sleep per night. The states with the shortest sleep duration include the states in the southeastern part of the US and the states along the Appalachian Mountains. Getting the most sleep were people who lives in states in the Great Plains. Americans in Hawaii have the highest percentage of adults who get fewer than seven hours of sleep per night whereas Americans in South Dakota get the most sleep.

Key findings of the current study showed that adults in their forties slept the least; adolescents went to sleep the latest, with different patterns during weekdays versus weekends; sleep efficiency decreased with age, but did have a relatively stable period from age 30-60; women had a longer sleep duration than men but only by a few minutes on average; non-Hispanic (NH) blacks sleep the least, the latest and had the lowest sleep efficiency in comparison with NH whites and Mexican Americans; and Mexican Americans had the earliest sleep onset, longest sleep duration, but second lowest sleep efficiency (only higher than NH Blacks) compared to other racial groups.

“Some findings have been expected from the literature, however, we are surprised by how late the adolescents go to sleep,” study author Xiaoling Wang told us. “Twenty-five per cent of the adolescents went to sleep after midnight. We were also surprised to see the disparities in sleep behaviors in Mexican Americans, which has not been reported before.”

The researchers believe more work needs to be done to understand the social and biological contributors to the disparities in sleep behaviors in different age, gender and racial group and their relevance to disease.