A new study has warned that people spending more time on their smartphones may suffer from poor sleep quality and less overall sleep.
Smartphones are increasingly becoming part of everyday life, but questions remain about the effects of frequent use on sleep.
Poor sleep is associated with health conditions such as obesity, diabetes and depression, researchers said.
Matthew Christensen from the University of California, San Francisco in the US and colleagues sought to test the hypothesis that increased screen-time may be associated with poor sleep by analysing data from 653 adult individuals across the US participating in the study.
Participants installed a smartphone application which recorded their screen-time, defined as the number of minutes in each hour that the screen was turned on, over a 30-day period.
They also recorded their sleeping hours and sleep quality.
The researchers found that each participant totaled an average of 38.4 hours over this period, with smartphones being activated on average for 3.7 minutes in each hour.
Longer average screen-time was associated with poor sleep quality and less sleep overall, particularly when smartphones were used near participants' bedtime.
The researchers state that their study is the first to measure smartphone exposure prospectively, but caution that the study also had some important limitations, including the self-selection of study participants and self-reporting of data.
While the findings cannot show causation or exclude the "effect-cause" that poor sleep could lead to more screen time, the association they found could fit with the theory that bedtime smartphone use may negatively impact sleep.
The study was published in the journal PLOS ONE.