Put simply, the effect of caffeine on heart rate is that the ingestion of caffeine increases the heart rate for a sustained period of time. The half life of caffeine in the body is generally around 6 hours, meaning the amount of time it takes for the body to eliminate half of the amount of caffeine consumed. It can take longer, however; sometimes up to 12 hours for caffeine to be completely eliminated from the body. For that entire time, the effect of caffeine on heart rate continues, causing the heart to beat faster and elevating blood pressure.
The effect of caffeine on heart rate occurs because caffeine stimulates the nervous system by affecting the body's production of a neurotransmitter known as adenosine, which acts as a calming force on the nervous system. If adenosine cannot be used by the body because of the presence of caffeine, this also stimulates the body to produce adrenaline, which leads to an increased heart rate and elevated blood pressure. These effects begin just a few minutes after consuming caffeine, and continue for the entire time the caffeine remains in the body. This can have serious implications for people who are sensitive to caffeine or who drink it every day.
Since caffeine is a stimulant, people who are especially sensitive to it might find that they have trouble sleeping even after having just one cup of coffee in the morning. It is generally recommended that people stop drinking coffee after noon, since it can easily impact sleep if it is consumed in the afternoon or evening. Switching to decaf at that point is a better bet. Since the effect of caffeine on heart rate causes it to beat faster, it may also affect breathing, leading to shallower breaths; this can make it more difficult to relax as well.
Consuming caffeine every day, and experiencing the effect of caffeine on heart rate, is not necessarily unhealthy if the heart is healthy, and the caffeine is consumed in moderation. To continue to experience the energy jolt, however, some people find that they have to continue to drink large doses of caffeine every day to get the same effect, which can potentially be dangerous. It is important to understand all of the sources of caffeine as well to keep track of the amount being consumed every day; this includes coffee, tea, as well as many soft drinks and energy drinks.
