Disturbed sleep patterns can trigger abdominal obesity, sudden cardiac death, anxiety and cardiac arrhythmias.  Many studies found a link between decreased testosterone levels and reduced sleep in men.  Men with the lowest testosterone levels had shorter periods of phases 3 and 5 sleep, the deepest periods of sleep.  Deep sleep phases disappeared completely in some men over 60 with low testosterone levels.  German scientists found that sleep deprivation during the early part of the sleep cycle had little effect on testosterone.  Sleep deprivation later in the sleep cycle caused marked decreases in testosterone.  Testosterone is important for synchronizing brain activity during sleep.  Low testosterone levels disturb brain function and interfere with sleep.  The effects of supplemental testosterone on sleep patterns are not known.  (Clinical Endocrinology, published online May 9, 2012)