1.   And flight attendants, who typically have disrupted sleep cycles, have elevated rates.

2.   An early discovery -- that it regulates sleep cycles -- prompted some manufacturers to incorporate it in sleep aids and jet-lag cures.

3.   But if you nap too much during the day, you may disturb your own nighttime sleep cycle.

4.   Different sleep cycles were tried.

5.   Heavy meals increase the desire for a siesta, but I think by now, through years of habit, my sleep cycle is permanently imprinted with that schedule.

6.   If you must sleep longer, nap for an hour and a half to complete a sleep cycle.

7.   In contrast, narcoleptics fall almost immediately into REM sleep and experience regular disruptions of their sleep cycle.

8.   MELATONIN This natural hormone, produced by a gland at the base of the brain, appears to help regulate your sleep cycle.

9.   Need to know more about sleep cycles and disorders?

10.   Setting your internal clock for regular sleep cycles requires discipline.