actually considerable medical concerns, right? >> i do. because sleep deficiency is associated with an increased risk of obesity and diabetes, affects the immune system and perhaps of greatest concern is the fact that it suppresses the release of the sleep-promoting hormone melatonin. in fact, people exposed to light during night shift work, that has been labeled as a carcinogen. >> what if it's a short period, like ten minutes? are you equally concerned? >> well, in our study, they read for several hours. the average teen spent ten hours of recreation nal media. ten minutes, we didn't evaluate