Something I occasionally wonder to myself after I down my third energy drink of the day: 'Is all this caffeine good for me?' Or maybe more realistically - 'How much harm is this actually doing?' And I know I'm not alone - as a matter of fact, four out of five Americans have caffeine of some kind on any given day, according to the Center for Science in the Public Interest. So what's this doing to our bodies and our health?

According to Wikipedia, caffeine is the world's most consumed psychoactive substance. It is a central nervous system stimulant, shown to increase alertness, reduce fatigue, and even increase performance. As caffeine metabolizes it also has the effect of increasing lypolosis - the breakdown of fat stored in fat cells.

Unfortunately, there are some negative consequences of regular caffeine consumption as well. One of the worst effects of chronic caffeine consumption seems to be its effects on the body's adrenal glands. Whenever we drink caffeine, stress hormones are released, triggering a 'fight or flight' response in our bodies - which wears off after an hour or so, and causing a 'crash' and the need for more. Done repeatedly over time, this overstresses the system, beats up our adrenal glands and fuels the 'fatigue spiral'.

Interestingly, tolerance to the substance builds very quickly. In fact, in one study, complete tolerance of subjective effects of caffeine was shown to develop after only 300 mg 3x a day for 18 days (study found here). That's really about the equivalent of three energy drinks a day - not all that much these days.

What's the verdict? One or two cups of coffee a day or an occasional Red Bull for that pre-workout pick-me-up is probably fine - and may even offer some health benefits. Like anything else, we just need to be careful not to overdo it - so enjoy that morning cup of coffee guilt-free!