Hi, let me just say that caffeine interferes with many reactions in our body. It has effect on our brain and many other organs. There are some studies that say that caffeine is a kind of addictive drug. These scientists have proven that it operates using the same mechanisms as, for example, cocaine. The effect of caffeine on our blood vessels is complex. In the brain, caffeine binds with adenosine receptors. Adenosine is a chemical that when bonded with nerve cells, among other things, causes the blood vessels to constrict. This is why many migraine drugs contain caffeine. The constriction of brain blood vessels eases the pain. On the other side caffeine also has a direct effect on the blood vessels in our body, especially on those in kidneys and lungs. The direct action causes the blood vessels to dilate. Because of these antagonistic effects the total result of caffeine effect on blood vessels is unpredictable. Basically, if you have one or two cups of coffee a day you should not feel any negative consequences of caffeine. However, if your daily intake of coffee is greater, you are seriously endangering your health.