Effects Of Caffeine On The Circulatory System

Caffeine is a naturally occurring substance in tea, coffee and chocolate. It is added to soft drinks and energy drinks in addition to being available in tablet form over the counter. Caffeine is widely recognized as a brain and nervous system stimulant. It also has direct effects on the heart and circulatory system. Much biomedical research has focused on whether the circulatory effects of caffeine cause any harm; the topic remains controversial.

Increased Peripheral Blood Flow

Caffeine causes relaxation of muscle cells in the blood vessels, except those in the brain. The blood vessels relax and expand, an effect called vasodilation. During vasodilation, blood flow is increased. Vasodilation coupled with caffeine's tendency to increase heart rate may cause a temporary increase in blood pressure. The American Heart Association states that daily consumption of 1 to 2 cups of coffee per day does not cause harm in people with high blood pressure.

Decreased Cerebral Blood Flow

In contrast to its effect on peripheral blood vessels, caffeine increases muscle tone in the blood vessels of the brain. This effect is called vasoconstriction, which reduces overall blood flow to the brain. Vasoconstriction caused by caffeine can help relieve headaches. Blood vessel spasms trigger some types of headaches. During a spasm, the blood vessel clamps down, restricting blood flow. After the spasm, a rebound vasodilation occurs, which may cause headaches. By keeping the blood vessels of the head in a steady state of vasoconstriction, caffeine interrupts the cycle of spasm and vasodilation, thereby reducing headache pain. Many over-the-counter and prescription headache remedies contain caffeine.
While caffeine in medications can be useful for alleviating existing headaches, dietary caffeine may trigger headaches, especially migraines. Caffeine levels in the blood vary throughout the day according to dietary consumption. Decreasing blood caffeine may cause rebound dilation of brain blood vessels, potentially triggering a migraine headache. Many doctors advise people with migraines to avoid caffeine because of its effects on brain blood flow.

Mixed Effects on Coronary Blood Flow

Caffeine may increase blood flow through the coronary arteries because of its vasodilating effects. However, greater oxygen demands due to increased heart rate may counteract the effects of increased coronary blood flow. To date, there is no conclusive evidence that caffeine's effects on coronary blood flow provide useful benefits. However, some research suggests caffeine may have a detrimental effect on coronary blood flow in people with pre-existing coronary artery disease. In a 2009 research study published in the journal "PLoS One," Dr. Mehdi Namdar and his colleagues concluded that caffeine hindered the normal increase in coronary blood flow typically seen with exercise. The effect of caffeine on coronary blood flow is an active area of research. Definitive conclusions about whether caffeine poses any significant cardiac risks have yet to be determined.