Using Your Phone at Night Can Make You Fat, Scientists Say

In today's 24-hour society, our activities are not dictated by the Earth's daily light-dark cycle. But our bodies still are.

Artificial light, night shifts, and social jet lag can confuse our internal body clocks, affecting our mood, sleep, alertness, and appetite. Back in 2011, a poll by the National Sleep Foundation found that nine out of 10 Americans reported using an electronic device before bed, with 72 percent of teenagers and 67 percent of young adults using their smartphones before bed.

Since this study was carried out, the percentage of Americans who own smartphones has more than doubled, and many more of us are now going to bed with our phones at our sides.

However, research has shown that this screen time can mess with our body's internal clock which, in turn, could be making us gain weight.

"Our sleep-wake cycles, alertness, mood, activity levels, core body temperature, and appetite fluctuate over the course of each day, under the control of the so-called 'master clock' in the brain," Becky Conway-Campbell, a research fellow at the Bristol Medical School at the University of Bristol in the U.K., told Newsweek.

"Other clocks throughout the body are termed peripheral oscillators, synchronized by neural and hormonal signals. One of the more powerful hormonal synchronizing signals is via large surges of cortisol (often known as the 'stress hormone') released from the adrenal glands in the early morning hours each day."

This daily cortisol burst can be modified by exposure to artificial light or changes in daily light exposure—which happens when we travel to different timezones—resulting in what is known as circadian misalignment.

"Circadian misalignment is caused by our internal body clocks being out of sync with external light-dark cues," Conway-Campbell said.

"As a population, we are now plagued by circadian disruption, by global light pollution that can be detected by satellites, and by the use of blue-light emitting devices late at night.

This circadian misalignment also disrupts the hormonal cycles that govern our body, leading to a range of adverse side-effects. "That may include symptoms such as brain fog, lethargy, chills in the daytime, overheating in the middle of the night, lack of appetite early in the day and excessive consumption later on," Conway-Campbell said.

To investigate the effects of hormonal disruption on eating behaviors, Conway-Campbell and her team applied cortisol-like hormones to a group of rats, either in sync or out of sync with their daily light-dark cycle. And the results were striking.

The rats whose hormone injections were in sync with their light-dark cycle ate 88.4 percent of their daily food intake during their active phase and only 11.6 percent during their inactive phase.

Meanwhile, the "jet-lagged" group whose hormones were injected out of sync ate 53.8 percent of their daily calories during their inactive phase, without an increase of activity during this time.

While this study—which was published on September 29 in the journal Nature Communications Biology—was carried out in rodents, these results suggest that disruption to our circadian cycle could drive our desire to eat late at night, which previous studies have shown is associated with metabolic disruption and weight gain, even when total calorie consumption remains the same.

As well as misaligned circadian cycles, our cortisol levels can also be affected by stress, which has also been associated with weight gain and unusual eating patterns.

More work needs to be done to understand the impact of these hormonal disruptions in humans and what can be done to mitigate their negative effects.

"These types of studies will ultimately provide information that will be used for intervention strategies for the treatment of obesity-related, metabolic disorders targeting the cause rather than the effect," Conway-Clark said.