Not getting enough sleep can make you sick, according to a new study. Writing in the journal Sleep, researchers from the University of Washington say sleep deprivation depresses the body’s immune system. To reach their conclusions, the researchers studied 11 pairs of identical twins with differing sleep patterns and found that the twin who slept less had a depressed immune system. Researchers noted that “genetics account for 31 and 55 percent of sleep duration,” with behavior and environment making up the rest. “What we show is that the immune system functions best when it gets enough sleep. Seven or more hours of sleep is recommended for optimal health,” said lead author Dr. Nathaniel Watson, co-director of the UW Medicine Sleep Center at Harborview Medical Center. Researchers said existing data on limited sleep deprivation in a lab setting “can increase inflammatory markers and activate immune cells,” but that less is known about long-term sleep deprivation in natural conditions. This study used “real world” conditions, according to researchers, which showed “for the first time that chronic short sleep shuts down programs involved in immune response of circulating white blood cells.” “The results are consistent with studies that show when sleep deprived people are given a vaccine, there is a lower antibody response and if you expose sleep deprived people to a rhinovirus they are more likely to get the virus,” Watson said. “This study provides further evidence of sleep to overall health and well-being particularly to immune health.” Citing U.S. Centers for Disease Control and Prevention, researchers said Americans are, on average, sleeping 1.5 to two hours less than the optimal amount, while one in three Americans sleeps less than six hours per night. “Modern society, with its control of light, omnipresent technology and countless competing interests for time, along with the zeitgeist de-emphasizing sleep’s importance, has resulted in the widespread deprioritization of sleep,” researchers wrote in the study.