Subtitles section Play video Print subtitles It's 11 PM. You should be asleep, but you're watching a video on your phone and tomorrow you'll wake up, and go to work, where you'll stare at a computer for eight hours. When you get home, you might even watch a movie on TV. So if you're anything like the average American adult, you spend more than seven hours a day staring at digital screens. So what's all this screen time actually doing to your body and brain? Surprise, surprise, humans did not evolve to stare at bright electronic screens all day so our eyes are suffering the consequences. An estimated 58% of people who work on computers experience what's called computer vision syndrome. It's a series of symptoms that include eye strain, blurred vision, headaches, and neck and back pain. And in the longterm this amount of screen time could be damaging our vision permanently. Since 1971, cases of nearsightedness in the US have nearly doubled, which some scientists partly link to increased screen time. And in Asia today, nearly 90% of teens and adults are nearsighted. But it's not just the brightness of our screens that affect us, it's also the color. Screens emit a mix of red, green, and blue light. Similar colors to sunlight. And over a millennia it was blue wavelengths in sunlight that helped us keep our circadian rhythms in sync with our environment. But since our circadian rhythms are more sensitive to blue light than any others, a problem occurs when we use our screens at night. Typically when the sun sets we produce the hormone melatonin. This hormone regulates our circadian rhythms, helping us feel tired and fall asleep. But many studies have found that blue light from screens can disrupt this process. For example, in one small study, participants who spent four hours reading e-books before bed for five nights, produced 55% less melatonin than participants that read print books. What's more, the e-book readers reported that they were more alert before bed, took longer to fall asleep and reach restorative REM state, and were more tired the next morning. But perhaps the most concerning changes we're starting to see from all this screen time is in kid's brains. An ongoing study, supported by the NIH has found that some preteens who clocked over seven hours a day on screens had differences in a part of their brain called the cortex. That is the region responsible for processing information from our five senses. Usually the cortex gets thinner as we mature, but these kids had thinner cortexes earlier than other kids who spent less time on screens. Scientists aren't sure what this could mean for how the kids learn and behave later in life, but the same data also showed that kids who spent more than two hours a day on screens scored lower in thinking and in language skill tests. To be clear, the NIH data can't confirm if more time spent staring at screens causes these effects, but they'll have a better idea of any links as they continue to follow and study these kids over the next decade. It's no doubt that screens have changed the way we communicate, but only time will tell what other changes are on the horizon for human kind.