Caffeine is a commonly consumed substance used to stimulate the central nervous system. A dose of caffeine alters neurotransmitter signaling to increase alertness and boost energy. Most people can drink 2 to 4 cups per day of coffee without experiencing significant side effects such as anxiety and headaches. However, in certain people, coffee may cause changes in heart rate.
Caffeine Functions
Caffeine can be found in many products including, coffee, tea, sodas and desserts. Regardless of mode of consumption, caffeine is absorbed and distributed throughout the body, states Medline Plus, of the National Institutes of Health. Once absorbed, caffeine passes through the bloodstream into the brain. In the brain, caffeine increases the amount of the excitatory neurotransmitter, glutamate, according to a June 2007 article in the journal "Synapse." Glutamate is the primary chemical signal in the brain that increases alertness. Caffeine is not stored in the body, but is metabolized and excreted in the urine many hours after consumption.
Effects on the Heart
Caffeine may affect the heart rate, particularly when consumed in excess. Specifically, Medline Plus states that caffeine may cause a fast heartbeat, or tachycardia. This occurs because caffeine may alter electrolytes that regulate heart rate. To test if caffeine affects your heart rate, feel your radial pulse, or the heartbeat on the thumb-side of your wrist, 30 minutes after consuming caffeine. If caffeine does affect your heart rate, it should return to a normal rate within a few hours.
Dangers of A Fast Heart Beat
A fast heartbeat is defined as a heart rate greater than 100 beats per minute. A fast heartbeat is a normal response to exercise; however, at rest it may be a sign of a serious heart complication. MayoClinic.com states that a fast heart beat may cause blood clots, fainting spells, inability to effectively pump blood or sudden death. Therefore, if you have heart disease, you should be cautious about consuming substances that may increase your heart rate.
Recommendations
If you are pregnant, have heart disease or peptic ulcers, you should ask your doctor how much caffeine per day is safe for you to ingest. If you are not at high risk, three 8 oz. cups of coffee is the average American intake. For most, drinking up to 10 cups per day is safe. Check with your doctor to make sure caffeine does not affect the medications you are taking.
References
- Synapse: "Caffeine Facilitation of Glutamate Release From Rat Cerebral Cortex Nerve Terminals (Synaptosomes) Through Activation Protein Kinase C Pathway: An Interaction With Presynaptic Adenosine A1 Receptors:" S.J. Wang, 2007.
- Medline Plus: Caffeine in the Diet
- MayoClinic.com: Tachycardia
- Medline Plus: Caffeine
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