Uncontrolled high blood pressure is becoming more common among Americans, putting them at increased risk for heart attack and stroke, a new study shows.

Previous research showed that in 1999-2000, 32.2% of Americans maintained blood pressure less than 140/90 mm Hg, but the rate rose to 54.5% in 2013-2014. However, the rate fell to 48% in 2015-2016.

Unfortunately, this new study found the proportion of adults aged 40-59 with successfully managed blood pressure fell nearly 10 percentage points from 2009 to 2018 (56.3% vs. 46.6%, respectively). Successful blood pressure management also fell among adults 60 and older by almost 6 percentage points from 2009 to 2018 (53.6% vs. 47.9%, respectively).

The study will be presented at a virtual American Heart Association meeting, being held Sept. 10-13. Such research is considered preliminary until published in a peer-reviewed journal.

"We cannot assume improvement in blood pressure management will continue, even after 35 years of success. High blood pressure is a serious health risk and deserves constant attention to prevent as many heart attacks and strokes as possible," said lead author Dr. Brent Egan, a professor at the University of South Carolina School of Medicine.

The reasons why fewer Americans have successfully managed blood pressure varies by age and requires further study, according to the researchers.

"A closer look at our findings revealed the fall in blood pressure control in older adults was mainly due to less effective use of blood pressure medication and management, so we need to focus on making sure the level of treatment is adequate for this age group," Egan said in a meeting news release.

The American Heart Association and American Medical Association have launched a national program called "Target: BP" in response to the high rate of uncontrolled blood pressure.