The results of a study by Korean scholars showed that short sleep duration and poor quality were significantly associated with an increased risk of non-alcoholic fatty liver disease (NAFLD) in the general middle-aged population. The study applied the Pittsburgh Sleep Quality Index (PSQI) scale to assess the sleep duration and sleep quality of 69,463 middle-aged workers and their spouses with biochemical and human testing, and ultrasonography to determine whether the subjects had fatty liver.