Sure, we know that screen time right before bed is bad for sleep. And turns out, using your smartphone late at night also makes you feel depleted in the morning, thereby making you less focused and engaged at work, according to a small new study.
The study, published in the journal Organizational Behavior and Human Decision Processes, had two parts. For the first part, 82 upper-level managers answered several surveys every day for two weeks. The surveys asked about their smartphone use for work, sleep quality and quantity, workplace engagement and feelings of depletion. Surveys were administered at 6 a.m. every morning (to determine smartphone use for work the night before, sleep and feelings of depletion in the morning), and 4 p.m. every afternoon (to gauge work engagement that day).
Indeed, researchers found that smartphone use after 9 p.m. was associated with decreased sleep quantity at night. That decreased sleep quantity was associated with morning depletion the next day, and morning depletion was associated with decreased work engagement for that day.
Researchers also ensured that reverse causality was not at play -- in other words, that having less engagement at work then leads to more smartphone use at night -- by using a type of mathematical model. But they found that "daily work engagement did not predict smartphone use that night," and "on a day to day basis, then, being engaged at work is not associated with subsequent smartphone use for work at night."
For the second part of the study, researchers surveyed 161 employees who worked in a wide range of fields (from dentistry to accounting), 136 of whom provided ample responses. The participants in this part of the study were administered surveys in the same manner as the participants in the first part of the study. However, for this part of the study, researchers also examined the use of other electronics -- such as desktop or laptop computers, tablets and TV -- to see how these may have affected sleep, morning depletion and work engagement.
Researchers found similar results to the first part of the study, where increased nighttime smartphone use increased morning depletion, which decreased workplace engagement. And interestingly enough, smartphones had a bigger effect in this chain than using a laptop or tablet or watching TV.
"Smartphones are almost perfectly designed to disrupt sleep," study researcher Russell Johnson, an assistant professor of management at Michigan State University, said in a statement. "Because they keep us mentally engaged late into the evening, they make it hard to detach from work so we can relax and fall asleep."
Exposure to excessive light at night could be doing more than hurting our ability to work the next day, too. A recent policy adopted by the American Medical Association recognizes that light at night -- including that from screens -- could increase the risk of disease, such as cancer, in addition to its sleep-disrupting effects.