Worldwide, more than 1.2 billion people were living with high blood pressure (hypertension) as of 2019, a number that has doubled in the past 30 years, according to a large international study published in the journal the Lancet.

Based on data from 1,201 studies involving 104 million people in 184 countries, the researchers projected that 652 million men and 626 million women have hypertension. Nearly half of them are unaware of their condition, and more than half are not being treated.

Although treatment and control of hypertension has improved in many countries, including the United States, about 45% of U.S. adults have hypertension or are taking medication to control it, and only 1 in 4 adults with hypertension has the condition under control, according to the Centers for Disease Control and Prevention.

Hypertension is considered a “silent killer.” Though it rarely has symptoms, the condition can cause serious, even life-threatening health issues. These include heart attack, stroke, heart failure and kidney failure. Your blood pressure — designated by two numbers — represents the force of your blood pushing against the walls of your arteries.

The first number (called the systolic pressure) indicates the pressure exerted when the heart beats, pumping blood from the heart into the arteries. The second number (called the diastolic pressure) indicates the pressure when the heart is at rest between beats. A reading for normal blood pressure would have a first number of less than 120 and a second number of less than 80.

High blood pressure is considered to be a reading of 140 or higher followed by 90 or higher. Treating high blood pressure usually begins with lifestyle changes, such as healthier eating, more exercise and losing weight. But medication may be prescribed if lifestyle changes do not get your blood pressure under control.