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 this week at the American Society of Hypertension''s annual meeting.

　　Researchers 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. They 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 smallsgroupsof 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. 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.

　　Researchers said that certain patients, such as those whose arteries are already stiff, may wish to start reducing caffeine consumption now.