Light from TVs, computers, tablets and smartphones may disrupt sleep and raise risk of obesity, heart disease and depression Watching TV or using computers, tablets or smartphones after dark may cause sleep loss and resultant health problems, a leading doctor has warned. Peering at brightly lit screens at night disrupts the body’s natural rhythms and raises the risk of medical conditions linked to poor sleep, including obesity, heart disease, strokes and depression, he said. The warning, from Charles Czeisler, director of sleep medicine at Brigham and Women’s Hospital in Boston in the US, comes as cheap electricity and more portable devices make it easier to surf the web, read books and check social media on glowing gadgets at any time of night. Artificial light can prevent a good night’s rest by dampening down the activity of neurons that bring on sleep, activating those for wakefulness, and suppressing the sleep hormone, melatonin.