The research: Michigan State University (MSU) researchers conducted two studies on smartphone use after 9 PM. The first surveyed 82 managers in the U.S., and the second surveyed 161 employees. Despite the different perspectives, using a smartphone for just 20 minutes resulted in noticeable increases in mental fatigue and disengagement from work the next day, says lead study author Russell Johnson, PhD, an assistant professor of management at MSU. Twenty minutes was considered above average use; excessive use ranged from 40-45 minutes. What it means: The blue light on smartphone screens inhibits the sleep hormone melatonin, which prevents sleep and thus increases your risk for bad moods and other major health problems (which we get into here). While the same light from TVs, laptops, and computers were taken into account, smartphones were the most invasive, says Dr. Johnson. “Smartphone displays are usually not covered, whereas laptops can be closed and many tablets are kept in sleeves or protective covers that flip down over the screen. When not in use, their displays are not distracting, unlike smartphones that light up or buzz to get users’ attention,” he says. To get through the night and your ongoing to-do list, Dr. Johnson suggests using smartphones for work activities within perhaps 30 or 60 minutes of one’s planned bedtime outside the bedroom. “Keeping the smartphone out of the bedroom helps people psychologically detach from work and helps maintain separation between work and recovery activities like sleep,” he says. This way, once you’re in bed, you’re free of temptation and interruptions. The bottom line: Before you move late night business to your laptop, know this: “An important ingredient for being cognitively rested and prepared the next day at work is to have a sufficient break from work the previous evening,” says Dr. Johnson. So it doesn’t matter which device you use to send that e-mail, text, or calendar update—it’s going to negatively affect you. More from Prevention: 8 E-mail Sins You Probably Commmited Today
