(CN) – Accurately and fully evaluating a person’s sleep quality has required costly and time-consuming methods that could only be used in sleep-focused labs – until now.
In a study published Thursday in the journal Current Biology, researchers present a new way of analyzing human sleep cycles over extended periods of time as individuals slumber normally.
The team’s findings are a critical breakthrough in sleep research as, for the first time, it will be possible to capture the real-life sleep habits and quality on a wide scale, according to the report.
“There has been practically no possibility of getting detailed sleep structures in a normal life setting over a long period of time,” said co-author Till Roenneberg, a professor of chronobiology at Ludwig-Maximilian University in Germany. “You can’t easily give somebody an EEG to take home and have next to the bed. You can’t do this over six weeks or six months. We are going to see things nobody has seen before.”
The new approach relies on a wrist-worn research gadget that is similar to commercial self-trackers like Fitbit. The gadgets, called actimeters and cost as little as $150, record wrist movements that can be used to document activity patterns for up to three months. The researchers used the actimeters to appraise rest and activity cycles over the course of an entire day.
The team reviewed actimeter data collected over more than 20,000 days from 574 subjects between the ages of 8 and 92.
The data, however, appeared messy and it was hard to recognize the cyclical sleep patterns typically seen with more complicated lab-based devices, according to the researchers.
They then noticed that by focusing on phases of night-time inactivity, a clearer cyclical pattern materialized. The researchers used a basic conversion to measure inactivity on a scale of near zero to 100, with 100 representing complete inactivity.
“It was flabbergasting how it clarified the structures,” Roenneberg said.
The researchers labeled the new scale “locomotor inactivity during sleep,” or LIDS. The measures demonstrated that movement patterns reflect sleep cycles and reproduce dynamics seen in lab settings.
While the data showed no sex differences in sleep dynamics – though men moved more than women – the team observed major differences between individuals based on their work schedules and age.
It was not evident at first how inactivity cycles correspond to patterns of rapid-eye movement (REM) and non-REM sleep typically assessed in the lab, Roenneberg said. Further analysis revealed that periods of least activity indicate deeper sleep. This is because during REM sleep, extremities often twitch, which the actimeter detects.
As the team collects additional data, they hope to develop more objective methods for measuring both sleep and sleep quality. These data are important for determining whether sleep interventions actually work.
“Right now, we’re not able to judge the outcome of interventions,” Roenneberg said. “If, for example, we change school times, is sleep quality changed? What about shift work times or indoor lighting? All interventions necessary to improve sleep today are only judged by sleep duration and by asking people how they feel they have slept.
“There’s no objective way to measure sleep quality, and we need this desperately.”
Roenneberg says the team is now ready to measure and compare the sleep habits and quality of individuals in various climates and latitudes, with different cultures and lifestyles. The researchers plan to develop online infrastructures that will allow people to upload actimetry recordings and receive important feedback on their sleep.
“Many devices have tried to use activity to assess sleep structures, but our method is simple, transparent, and works especially in long-term recordings,” Roenneberg said.
“This will help many who have sleep problems and will hopefully increase the appreciation for the importance of sleep for our health and well-being.”