According to the NIH, Sleep is one of the events that modify the timing of secretion for certain hormones. Many hormones are secreted into the blood during sleep. For example, scientists believe that the release of growth hormone is related in part to repair processes that occur during sleep.
Right, and what first came to mind for me was Melatonin. I was looking into sleep hacks a couple years back and studying up on Melatonin drove me away from trying out anything that would disturb a "normal" amount of time sleeping in the dark. I remember seeing a study that linked a lack of Melatonin production to some kinds of cancer. Can't seem to find it now.
http://science.education.nih.gov/supplements/nih3/sleep/guid...