Tina Kold Jensen of the University of Southern Denmark and colleagues said they found the sleep-deprived men also had a higher risk of lower testosterone levels and observable testicular size shrinkage.
Jensen and colleagues surveyed 953 men in their late teens and early 20s. All of the men delivered a semen sample, had a blood sample drawn, underwent a physical examination and answered a questionnaire including information about sleep disturbances.
Sleep disturbances were assessed on the basis of a modified four-item version of the Karolinska Sleep Questionnaire, which includes questions on sleep patterns during the past four weeks.
The study, published in the American Journal of Epidemiology, found men with sleeping problems -- insomnia, staying awake late, inconsistent sleep -- had an almost 30 percent lower sperm count, their sperm was more deformed, and their testicles were smaller.