Sleep loss may impact male fertility

This article discusses how sleep problems may be associated with male fertility problems. Researchers surveyed young men around 18 years old and tested a sample of their sperm. Those that had disturbed sleep (not defined in the article) or slept less than 6 hours had 29% reduced sperm concentrations. They also had reduced sperm quality and smaller testicles. What's not clear is why these men had disturbed sleep - was it from a sleep disorder or voluntary sleep deprivation? If it's the latter, than more sleep may help couples that have trouble conceiving.