It only takes 60 to 90 minutes of exercise a week to significantly lower blood pressure, Japanese researchers reported. That amount of aerobic exercise spread out over a week reduced systolic blood pressure -- the top number on a blood pressure reading -- an average of 12 points and the lower or diastolic reading by 8 points, the researchers found. Doctors consider optimal blood pressure to be 120/80 or lower. "This study confirms the importance of exercise," Dr. Michael Weber, an editor at the American Journal of Hypertension, which published the study, said in a statement. "The investigators found a person does not have to spend great amounts of time working out." Many guidelines currently call for anywhere between half an hour and an hour of moderate exercise on most days of the week to reduce the risk of heart disease, cancer, diabetes and obesity. Kazuko Ishikawa-Takata and colleagues at Japan's National Institute of Health and Nutrition tested 207 men and women who had high blood pressure but were otherwise healthy. None exercised regularly. They divided them into five groups who got a range of exercise from none to two hours and more a week. The volunteers in the four groups that exercised worked out with a trainer at a health club for eight weeks. Those in the group that got 60 to 90 minutes of exercise had the greatest drop in blood pressure. "There were no greater reductions in systolic blood pressure with further increases in exercise volume," the researchers said. They said their findings should encourage people who think they cannot exercise enough to improve their health. "We should emphasize that our present results should not be viewed as a message against encouraging people to exercise more on a daily basis," the researchers wrote. High blood pressure is becoming more common around the world. Nearly 50 million Americans -- 23 percent of the population -- have high blood pressure of 140/90 or more. It can lead to strokes, heart attacks and kidney failure.