Increased heart rate is a common side effect for individuals who consume more than 300 mg of caffeine a day. While most people are familiar with the pleasant buzz following a cup of joe, not everyone understands the intricate biochemical responses that the body has from coffee. For best results, keep your consumption below the recommended 200 to 300 mg of caffeine -- roughly two to three cups of coffee a day.
Caffeine and the Heart
As coffee enters the digestive system, the caffeine quickly passes to the brain via the blood. Once there, it begins to mimic the characteristics of a neurotransmitter called adenosine that is responsible for sensations of drowsiness, inhibiting feelings of tiredness. As your pituitary gland begins releasing stress hormones, your heart becomes stimulated and your vessels begin to dilate, increasing blood pressure and causing a bronchial relaxation effect similar to those caused by anti-asthmatic drugs. According to the Virtual Mass Spectrometry Laboratory website, these cardiovascular effects occur each time you drink a cup of coffee, although your body may gradually increase in tolerance.
Increased Heart Rate
Although the increase in blood pressure may be modest, the Harvard Medical School website warns against the larger concern of occasional irregular heartbeats. Depending on your levels of caffeine dosage and sensitivity, your heart rate might increase considerably, potentially leading to slight sensations of dizziness or nausea.
Long-term Effects
Coffee generally reaches its highest concentration in the blood within an hour after consumption and is removed from the body by way of urination after several hours. Since caffeine isn't stored in the blood or tissues, the only long-term heart effects from caffeine are the withdrawal symptoms that may develop from a caffeine dependency. The Mayo Clinic recommends a moderate intake of 200 to 300 mg of caffeine a day for healthy individuals and warns that an intake of 500 to 600 mg of caffeine -- or four or more cups of coffee -- can lead to unpleasant symptoms such as restlessness, upset stomach, jitteriness, muscle tremors, insomnia and irritability. Severe cases of caffeine overdose have occasionally led to death due to irregular heartbeat.
Safety Concerns
Talk to your doctor if you experience a rapidly increased heart rate or irregular heartbeat after consuming moderate doses of caffeine. If you suspect that you may be intolerant or allergic to coffee, quit drinking coffee. Coffee taken in conjunction with other caffeinated products, such as chocolate, sodas and teas, may increase your risk of excessive caffeine intake.
References
- Mayo Clinic; Caffeine: How Much is Too Much?; March 9, 2011
- Medline Plus; Caffeine Overdose; Jan. 17, 2010
- Virtual Mass Spectrometry Lab: Caffeine Effects
- Medline Plus; Caffeine in the Diet; May 2, 2009
- Harvard Medical School; Coffee Health Risks; August 2004
- PubMed; Central Nervous System Effects of Caffeine and Adenosine on Fatigue; February 2003
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