Caffeine Loses Effect For The Overtired, Study Finds

BOSTON (CBS) -- If you relying on a cup of coffee to keep you awake after a few bad nights of sleep, think again.  In fact, caffeine can lose its "jolt" if you're just too exhausted.

In a U.S. military study, researchers looked at 48 volunteers allowed only five hours of sleep a night for five nights then given caffeine equivalent to two cups of coffee and then a battery of tests.

For the first few days, those who took caffeine had better test results than those on a placebo, but that competitive edge was lost after three nights of limited sleep.

Again stressing the importance of getting good rest and not relying too heavily on caffeine to keep you bright-eyed and bushy-tailed.