People worldwide are checking their blood pressure as part of a campaign to alert people about the dangers of high blood pressure.

Companies and organizations worldwide are participating in the World Hypertension League’s effort to get more people to check their blood pressure, culminating in World Hypertension Day on May 17. The league aims to track 25 million screenings.

More than one in five adults worldwide — about 1.13 billion people — have high blood pressure, which causes about half of stroke and heart disease deaths globally, according to the World Health Organization.

Nearly 86 million Americans have high blood pressure, and only half have it under control, according to statistics from the American Heart Association. It’s known as the “silent killer” because it doesn’t cause obvious symptoms, resulting in about 16 percent of Americans being unaware they have the condition.

High blood pressure, also known as hypertension, raises the risk of heart attacks, strokes and kidney disease. Hypertension occurs when someone’s reading is 140/90 mm Hg or higher. The optimal blood pressure for people 20 and older is under 120/80 mm Hg.

“Hypertension is a priority issue for the American Heart Association, as it is a condition that underlies many other cardiovascular conditions,” said Steven Houser, Ph.D., director of the Cardiovascular Research Center, professor of medicine and professor and chair of physiology at Temple University School of Medicine. Houser is also president of AHA, which is participating in the global blood pressure-check effort, known as the #CheckIt challenge.

“Increasing global awareness of hypertension, and how to manage it through campaigns such as World Hypertension Day and the #CheckIt challenge help us move closer to that goal,” he said.

The AHA and its network of U.S. partners reported nearly 2 million checks as of Wednesday, based on its #CheckIt challenge data for April and May. The AHA’s goal is to get 5 million checks by the end of the month.

The AHA gathered more than 16,000 blood pressure checks through online efforts, including its Check. Change. Control. program tracker.

Other U.S.-based participants include PharmaSmart, a network of 7,000 scientifically validated kiosks found in pharmacies, drug and discount stores, which recorded more than 840,000 blood pressure tests. Omron, which manufactures blood pressure monitors, tracked more than 1 million blood pressure checks from connected monitors and apps. And A&D Medical, which also manufactures blood pressure monitors, recorded 12,500 blood pressure checks.

Editor’s Note: This story was written when high blood pressure was considered 140/90 or higher. New guidelines released in November 2017 changed the definition to 130/80.