(HealthDayNews) -- Three or four cups of coffee can help you wake up, but do you know they can hurt you in the long run?
Caffeine makes your nerve cells do the cellular equivalent of shout at each other. Nerve cells normally send chemical messengers, called neurotransmitters, across the gaps between them. The more neurotransmitters a cell receives, the more it responds with adenosine. When the sender gets adenosine back, it reduces the amount of the neurotransmitter it is sending so the receiving cell won't be overwhelmed. But caffeine blocks the adenosine from the sending cell, so the sending cell never turns down the volume. That's why caffeine can help your performance on boring tasks like staying awake on a long drive. But if you're stressed already, you'll get jittery.
Stimulating your nerve cells in this way can also raise your blood pressure. Psychosomatic Medicine reports that 19 volunteers who were given caffeine pills had their blood pressure recorded during a normal workday. On a dose of 500 milligrams -- about what's found in four or five cups of coffee -- their blood pressure went up about five points. Think about that the next time you reach for a refill.
