A new study says that sound sleep is important for the well-being of the immune system and it makes it stronger too. The findings, published in the journal Sleep, showed that chronic short sleep shuts down programs involved in immune response of circulating white blood cells. Researchers from University Of Washington Health Sciences in the U.S. found that participants with shorter sleep duration had a depressed immune system. “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 from Harborview Medical Center in the U.S. They took blood samples from 11 pairs of identical twins with different sleep patterns. A unique feature of this study was to employ identical twins in order to control for the large genetic determinant to humans’ sleep duration. The researchers explained that genetics account for 31 to 55 percent of sleep duration and behaviour and environment account for the remainder.The researchers, citing data from the Centers for Disease Control, said that over the past century people in the United States are sleeping an estimated 1.5 to two hours less, and about one-third of the working population sleeps less than six hours per night.