Your car's dashboard has several different warning lights, some of which might lead you to check your fluid levels. If only your body had the same kind of warning system. In fact, we're equipped with a weak thirst detector, and the mechanism only kicks in when dehydration becomes fairly serious [source: Napier]. As a result, many of us are walking around mildly dehydrated, which puts huge demands on our energy levels. Without a hydrated body, blood circulation slows down, which means that blood, with its valuable nutrients and oxygen, isn't getting to your muscles.
But hey, if you really want a beverage that packs a punch in terms of energy, you're more likely to turn to soda or coffee, right? This does more long-term damage, since these hits of caffeine intensify dehydration by causing more frequent urination. Caffeine also takes about 10 or 12 hours to completely disappear from the bloodstream, so consuming it in the late afternoon or evening can prevent you from getting those critical hours of sleep [source: Liu].
Maybe, though, you feel you're too far gone with a caffeine habit that you can't stop now. After all, a day without coffee gives you headaches and energy slumps as well, so shouldn't you stick with it? Don't quit caffeine cold turkey, but withdraw gradually. And if you want a real energy hit, drink water.