Caffeine may be vegan, but it is not ok. It is additive, excitatory, and harmful as well.
Here are just a few harmful effects on your body system: (Thanks to Rachel and Lisa Krum for some of this info.)
Heart and circulatory system: Studies show that “ 250 milligrams of caffeine can decrease central blood flow by 20-30%.” 7oz (approx 1c) drip coffee has 150mg of caffeine or in two cups you are really affecting your circulatory system. One study showed when caffeine and placebo days were compared, the researchers found blood pressure to be consistently higher on the caffeine days -- an average of 4 millimeters (mm) higher for systolic pressure and 3 mm for diastolic. So it decreases blood flow, but increases blood pressure. Not a good combination.
The brain - addictive: “When your brain is tired and wants to slow down, it releases a chemical called adenosine. Adenosine travels to special cells called receptors, where it goes to work counteracting the chemicals that stimulate your brain. Caffeine mimics adenosine; so it can "plug up" your receptors and prevent adenosine from getting through. Result: Your brain never gets the signal to slow down, and keeps building up stimulants. After a while, your brain figures out what’s going on, and increases the number of receptor cells so it has enough for both caffeine and adenosine. When that happens, caffeine can’t keep you awake anymore … unless you increase the amount you drink so it can "plug up" the new receptor cells as well. This whole process only takes about a week. In that time, you essentially become a caffeine addict. Your brain is literally restructuring itself to run on caffeine; take the caffeine away and your brain has too many receptor cells to operate properly."
The brain - are you in control? "We know that caffeine is the most widely used mood-altering drug in the world," says Roland Griffiths, a professor in the departments of psychiatry and neuroscience at the Johns Hopkins School of Medicine, who has studied caffeine extensively. "It is estimated that as much as 80 percent of the world's population consumes caffeine in one form or another."
Hormones: One study showed: Stress hormone levels rose by an average of 32% and both the blood pressure and adrenaline increase lasted throughout the day and into the evening. Thus it raises cortisol (the stress hormone) levels in the body.
Affects pregnant women: Experts say that caffeine should be avoided during pregnancy. Drinking coffee during pregnancy has been linked to lower birth weight and an increased risk of miscarriage and stillbirth, though there is no proof at this point that caffeine itself causes miscarriages, according to the American College of Obstetricians and Gynecologists. "We don't really know what the health effects of caffeine are for the fetus," van Dam says.
Can cause weight gain: Caffeine causes a short-term elevation in your metabolism, which gives you a burst of energy. Like any addiction, however, as your body becomes accustomed to caffeine, it begins to compensate. Used over the long term, caffeine actually reduces your metabolism. The slower metabolism actually causes you to gain weight on less food.
Affects blood sugar: It causes your blood sugar to increase. Then after the caffeine begins to wear off your blood sugar plummets. This causes you to possible even crave sugar.
What about the health benefits. I heard coffee helped reduce the risk of diabetes, stroke, parkinson's, and other disease? Results from studies was clear, decaffeinated coffee was just as effective, if there was any benefit at all!!! Researches say the evidence is just not conclusive at this point. (2009) In fact, while they found it MAY help insulin levels, it increased blood sugars, so the benefits are not as beneficial as Java brewers would like you to believe.
The problem is the caffeine is still harmful in other ways. Leave the caffeine out of the cup!!!