When men reach age 30, testosterone levels begin to drop by 1 to 2 percent annually, researchers say. Coincidentally, many men begin to complainat around age 40 about the quality of their sleep. Are the two linked?

Yes, one new study concludes.

The research revealed a link between testosterone levels in men over 50 and the amount of deep sleep they report.

"Deep sleep is when the recuperation of body and mind is optimal,"said study leader Zoran Sekerovic, a graduate student from theUniversity of Montreal Department of Psychology.

In young men, deep sleeprepresents 10 to 20 percent of total sleep, Sekerovic explained in astatement. By age 50, it decreases to as little as 5 percent. For menover 60, it can disappear altogether, the study found.

The study didn't find any correlation with other parts of the sleepcycle: falling asleep, light sleep, or paradoxical sleep, when most dreams occur. Men in their 20s don't have such a correlation, because their neuronal circuits are intact, the thinking goes.

"With age, there is neuronal loss and the synchronization ofcerebral activity isn't as good, which is why there is a loss of deepsleep," Sekerovicexplained. "Low levels of testosterone intensify the lack ofsynchronization and can explain 20 percent of men's inability toexperience deep sleep."

Sekerovic suggests dwindling testosterone levels are what impact sleep,not vice-versa, as other studies have suggested. He adds previousinvestigations measured daily fluctuations in testosterone levels,which are higher in the morning.

If his findings are true, there could betreatment options.

"The loss of deep sleep is a serious problem that could be treatedwith testosterone. That would be tremendous progress," he said. "But hormone therapy can have secondary effects.Therefore, it will be essential to better understand the mechanismsleading to the loss of deep sleep."

Other scientists have suggested, however, that older people need less sleep.

This study, announced Friday, was supervised by Julie Carrier, aprofessor of psychology at the University of Montreal. The findingswere presented at the annual conference of the Association francophone pour le savoir (ACFAS).