You should avoid using your smartphone before bedtime if you don't want to get fired from work. Checking business related emails or scrolling through your friends' social media updates late at night may seem harmless but it can sap the energy you need to be focused and efficient at work during the day, making you less of the employee your company wants to retain.

Researchers of a new study that will be published in the journal Organizational Behavior and Human Decision Processes, asked 82 upper-level managers to answer surveys that would determine their smartphone use for work in the evening, quality and quantity of sleep, feeling of depletion in the morning and work engagement during the day. The researchers found that smartphone usage after 9 PM can decrease the respondents' quality of sleep and deplete their energy the next day.

"Smartphones are almost perfectly designed to disrupt sleep," said study researcher Russell Johnson, an assistant professor of management at Michigan State University. "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."

The researchers also surveyed 161 employees working for different industries and yielded the same result. For the second group of respondents though, the researchers also examined their use of other electronic devices such as tablets, TV and computers to see how these may affect their sleep, morning depletion and work engagement. The researchers found that using smartphones at night had worse effect than using other electronic devices.

"It can be a double-edged sword," Johnson said. "The night-time use of smartphones appears to have both psychological and physiological effects on people's ability to sleep and on sleep's essential recovery functions."

The "blue light" emitted by smartphones likely contributes to sleep disruption because it hinders the release of melatonin, a chemical in the body that helps regulate sleep and wake cycle.

The best solution to avert the negative consequences of bedtime smartphone usage is to turn off the smartphone at night albeit the researchers admit this may not always be the most practical solution. "There may be times in which putting off work until the next day would have disastrous consequences and using your smartphone is well worth the negative effects on less important tasks the next day," Johnson said. "But on many other nights, more sleep may be your best bet."

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