It`s the leading contributor to deaths worldwide yet most people with high blood pressure don`t know they have the condition and even for those who do, treatment is mostly ineffective, according to a large new study.

Researchers examined more than 140,000 adults in 17 countries and found that about 41 percent had consistently high blood pressure, also known as hypertension, but fewer than half of those people knew it.

"We found that surprisingly many people didn`t realize their blood pressure was high," lead author Clara Chow, from The George Institute for Global Health in Sydney, Australia, said.

Less than a third of those aware of their condition and getting treatment had their blood pressure under control, with poor and rural populations faring the worst.

"Whereas in high-income countries a larger proportion of people knew they had hypertension and were on treatment than people in low-income countries, the control problem was significant wherever you were," Chow said.

Normal blood pressure is defined as a systolic reading (the top number) of 120 millimeters of mercury (mm Hg) or less and a diastolic reading (the bottom number) of 80 mm Hg or less.

The National Institutes of Health estimates that one in three U.S. adults has high blood pressure, which can lead to heart disease, heart failure, stroke and kidney failure.

High blood pressure is the leading cause of heart disease and strokes, which are the top two causes of death worldwide, according to the World Health Organization.

Globally, hypertension is tied to "at least" 7.6 million deaths each year, Chow`s team writes in The Journal of the American Medical Association.

Despite the condition`s worldwide impact, Chow told Reuters Health, there hasn`t been much research on how it should be targeted to bring down the incidence of cardiovascular disease.

For the new study, she and her colleagues from several research centers around the world recruited 142,042 adults in 17 countries of varying income levels to be examined between January 2003 and December 2009.

They defined the condition either by a participant`s self report of having been diagnosed with hypertension, or by two blood pressure readings of at least 140/90 mm Hg.

Overall, 57,840 of the participants had high blood pressure, but only 26,877 were aware of their condition.

The vast majority of those who were aware were taking some sort of medication - often two medications - to treat high blood pressure, but only about one third were successfully controlling the disease.

"People who knew they had hypertension, about 88 percent were initiated on some sort of treatment. However the control of their blood pressure was poor," Chow said.

When researchers looked at the results by country, they found that in high-income and upper-middle-income countries, around 50 percent of people with high blood pressure were aware of their condition and around 47 percent were getting treatment.

In comparison, in lower-income and lower-middle-income countries around 42 percent of people with hypertension were aware of it and about 34 percent were treated.

In poorer countries, awareness, treatment and control of high blood pressure were better in urban areas compared to rural ones, and among better educated people, the researchers note.

Dr. Jorge Plutzky, director of the Vascular Disease Prevention Program at Brigham and Women`s Hospital in Boston, said the new study confirms previous findings on blood pressure around the world and adds to what is known by showing the differences between urban and rural areas.

"I think it`s another stimulant to get a variety of groups to look at and think about this issue," Plutzky, who was not involved in the new study, said.

For example, he said, international groups have been effective in combating a variety of infectious diseases throughout the world.

"We need those same kinds of groups to also start thinking about chronic diseases," he said, adding that techniques developed overseas can also be brought back to rural areas in the U.S.

Chow said the focus should be on finding ways to detect high blood pressure in people in different places around the world, and removing barriers to treatment, including costs and transportation to and from doctors` offices.