A new study found a link between sleep duration and a measure of chromosomal health in sperm. In the study of 2020 semen samples provided by 796 male volunteers from colleges in Chongqing (China) from 2013 to 2015, volunteers with more than 9 hours per day of sleep and those with 6.5 hours or less per day sleep had 41% and 30% lower High DNA Stainability —- an index that represents the proportion of sperm with abnormal chromatin —- than did volunteers with 7 to 7.5 hours per day of sleep.