Ask an Expert: How does caffeine affect the heart?

Q: “How do different kinds of caffeine (coffee, tea, soft drinks, energy drinks) affect the cardiovascular system?”

Answer from Ty Gluckman, M.D., cardiologist, Providence St. Vincent Heart Clinic – Cardiology:

Many studies have looked at the effects of coffee, and some have looked at the effects of tea and soft drinks (energy drinks, which are newer, have not been studied as much). None of these studies has offered any evidence to suggest that different sources of caffeine affect us in different ways.

Based on the data that we have, the effects of caffeine on the cardiovascular system appear to be mild, short term, and related more to the quantity rather than the source of the caffeine.

In general, caffeine affects the cardiovascular system in several ways:

  • In people who don't consume caffeine very often, it can cause systolic blood pressure (the top number in your blood pressure reading) to rise in the short term by as much as 10 points. In habitual caffeine consumers, this effect is much less pronounced.
  • Caffeine can act on enzymes in the heart that stimulate the intensity of the heart's contractions.
  • Caffeine can facilitate the release of natural hormones that act on the heart to release norepinephrine, which can produce a stimulated effect similar to that of adrenaline.
  • At higher levels, caffeine can increase the amount of calcium inside the cells in the heart. Since all of the cells involved in the heart's squeezing and relaxing are regulated by calcium, an increase can affect the heart's pumping action.

For some people, these biologic effects cause no symptoms at all. Others may feel like their heart is pounding, racing or beating irregularly. But despite these short-term biologic effects, no study has demonstrated any appreciable harm or long-term problems caused by caffeine. This is true both for people who are perfectly healthy and for people who have been diagnosed with cardiovascular disease.

Two large epidemiological studies observed people over time to determine whether there was a relationship between consumption of caffeine (the studies looked at coffee, tea and soft drinks, but not energy drinks) and the development of heart disease, cardiovascular disease or cerebrovascular disease. Neither the Health Professionals Study nor the Nurses Health Study was able to demonstrate any relationship between caffeine consumption and increased risk.

Studies done in people diagnosed with cardiovascular disease also have failed to demonstrate a definitive effect. Nonetheless, because caffeine is a stimulant, people who have abnormal heart conditions or high blood pressure should discuss caffeine intake with their physician.

The stimulant effects of caffeine have raised concerns about the potential for causing abnormal heart rhythms. However, although caffeine can cause short-term effects that mimic the symptoms of a heart rhythm abnormality, very detailed, well-done studies have failed to demonstrate that it can actually cause a rhythm disorder.

One small study done in Costa Rica did suggest that genetic makeup may predispose some people to higher cardiovascular risk when they accumulate caffeine at very high levels. This study looked at how we metabolize caffeine. It found that abnormalities in the enzymes that metabolize caffeine can lead some people to metabolize caffeine very slowly, allowing it to build up in their systems. In these “slow metabolizers,” high accumulations of caffeine may pose a higher risk for adverse cardiovascular effects.

Consuming very high doses of caffeine is generally not recommended for anyone. Doses of 500 mg or more can cause “caffeine intoxication,” a diagnosis listed in both the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) and in the International Classification of Diseases and Related Health Problems (ICD-10). Symptoms may include anxiety, panic attacks, elevated blood pressure, increased gastric acid, bowel irritability and insomnia, depending on an individual's tolerance to caffeine. These symptoms usually go away as soon as the caffeine leaves the system, however, and there are no lasting consequences.

For people who are heavily dependent on caffeine, the absence of caffeine can cause problems, as well. Withdrawal can cause sweating, headaches, fatigue and other unpleasant symptoms.

In general, however, the preponderance of evidence does not suggest any lasting, harmful cardiovascular effects related to caffeine.

Dr. Gluckman's clinic location

Providence St. Vincent Heart Clinic - Cardiology
9427 SW Barnes Road, Suite 498
Portland, OR 97225

July 2010