Analysts at the Department of Health and Human Services Agency for Healthcare Research and Quality said the 55 million figure reflects only those who had their blood pressure measured in 2008, the latest year for which numbers are available.
"Because high blood pressure has no symptoms, the real total would have to include people who have high blood pressure and don't know it," Karen Davis of the Agency for Healthcare Research and Quality said in a statement. "High blood pressure can lead to heart attack, heart failure and stroke. But it can be controlled -- even prevented -- by proper eating and physical activity."
Researchers found those who exercised vigorously 30 minutes or more at least three times a week were one-third less likely than others to have high blood pressure, Davis said.
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