When that triple-shot espresso is just too much

Your nerves jangle like a ringing phone as you race to meet work deadlines.

But is your job really all that stressful, or is your anxiety percolating from the triple espresso shots you gulp down every day in your lattes? With gourmet coffee outlets on every corner, and serving cups almost the size of Big Gulps, people are drinking coffee by the quart.

Caffeine isn't an absolute no-no for most healthy adults, and researchers have been unable to find conclusive links between caffeine and dire health problems, such as heart disease and cancer.

But caffeine over-consumption is a concern among dietitians.

Too much caffeine can become part of a vicious cycle of poor health habits, which can end up making you tired and lethargic - exactly the opposite effects you sought from that rich Italian dark roast.

More than half - 52 percent - of American adults drink coffee every day, according to the National Coffee Association, and another 28 percent drink coffee occasionally.

In today's go-go world, people look to caffeine as a magic bullet to get more done on less sleep, says Martha Holland, a community dietitian at Carson-Tahoe Hospital in Carson City.

But the magic of a caffeine buzz is only an illusion.

"You don't really have that much zip.

You just feel like you do."

The trouble comes when that false sense of zip gives you the jitters and ends up zapping your sleep habits.

Tolerance to caffeine builds over time, so it takes more and more to get the same effects.

Over-consumption of