Caffeine is a stimulant. Sure, it makes you more awake and focused, but along with that immediate speed-up affect on your brain comes the speed-up affect on the heart and blood. Because it's a vasoconstrictor, or substance that narrows blood vessels, caffeine raises blood pressure — from just a few points in some, to huge numbers in others. (The American Psychosomatic Society attributes 20 percent of all stroke-related deaths to caffeine consumption.) Eliminating it from your diet can restore your blood pressure to normal healthy levels, or at the very least, help you avoid huge spikes every time you pour a cup of coffee.