By Alison McCook
NEW YORK (Reuters Health) - Small doses of caffeine--even as little as that in one cup of coffee--can cause temporary stiffening of the blood vessel walls, according to two small studies released here this week at the American Society of Hypertension's annual meeting.
Researchers led by Dr. Charalambos Vlachopoulos of Athens Medical School in Greece looked at the effect of caffeine in people with mild hypertension, or high blood pressure, and in individuals with normal blood pressure.
The researchers found that people with mild hypertension who took a pill that contained 250 milligrams (mg) of caffeine, equivalent to the amount contained in 2 to 3 cups of coffee, experienced a temporary increase in blood pressure and in the stiffness of the aorta, the main artery leaving the heart.
In the other study, a small group of people with normal blood pressure who were given a pill containing as much caffeine as one cup of coffee also experienced a temporary increase in the stiffening of arterial walls.
Vlachopoulos and his team measured arterial stiffness by looking at pulse velocity in the aorta.
Arteries need to be supple enough to expand when muscles--including the heart--demand more oxygen, and a loss of elasticity spells trouble for the body. Arterial stiffening places an extra load on the heart, and is a primary cause of hypertension.
In the general population, hypertension is a major risk factor for serious conditions such as heart disease, stroke and kidney disease. Blood pressure is considered high when systolic pressure--the first number in a blood pressure reading--is above 140 mm Hg, and diastolic pressure--the second number in the reading--goes over 90 mm Hg.
In the first study, Vlachopoulos and his team gave 10 mildly hypertensive people a high-dose caffeine pill and placebo. Caffeine increased systolic pressure by 11.4 mm Hg relative to placebo.
In the other study, the caffeine equivalent of one cup of coffee also increased arterial stiffness in 10 non-hypertensive patients, and raised their systolic blood pressure by 3 mm Hg and their diastolic reading by 6.5 mm Hg.
Pulse velocity eventually returned to its normal levels, Vlachopoulos noted, but remained higher than average even three hours after patients took the caffeine pills.
Vlachopoulos explained that the increased arterial stiffness that comes with caffeine might worsen hypertension in people who already have high blood pressure, and may also increase the risk that these individuals have of suffering a serious cardiovascular event such as heart attack or stroke. The increased stiffness also reduces the amount of oxygen that is supplied to the heart, he noted.
Both studies used only a small number of patients, the Greek researcher noted, and further research is needed before doctors can make specific recommendations about who should avoid caffeine and who should simply reduce the amount they consume.
In the meantime, however, Vlachopoulos said that certain patients, such as those whose arteries are already stiff, may wish to start reducing caffeine consumption now.
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