Though high blood pressure is the leading cause of cardiovascular disease worldwide, many adults who have it don't get diagnosed with, let alone treated for, the condition.

This is one of the key findings of a 10-year, international study spearheaded by the McMaster University's Population Health Research Institute (PHRI) in Hamilton, Ont., that examined the health of more than 150,000 adults aged 35 to 70 in 17 countries.

'We found that when we measured people's blood pressure, less than half knew they had high blood pressure.'—Dr. Koon Teo, Population Health Research Insititute

In a paper published in the September issue of the Journal of the American Medical Association, the authors write that only 46.5 per cent of the participants who had high blood pressure, or hypertension, had been diagnosed with the condition before getting involved in the study.

"We found that when we measured people's blood pressure, less than half knew they had high blood pressure," said Dr. Koon Teo a professor of cardiology at McMaster University and an investigator with the PHRI. "Among those who knew they had high blood pressure, only about one-third were being treated."

Reducing risks

The suggestion that many millions of adults worldwide have undiagnosed or simply untreated hypertension has serious implications, said Dr. Clara Chow, a cardiologist with the George Institute for Global Health in Sydney, Australia and the report's lead author.

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Dr. Clara Chow is a cardiologist with the George Institute for Global Health in Sydney, Australia. (Supplied)

"Hypertension is the leading cause of cardiovascular disease globally," she said of the condition, which is linked to 7.6 million deaths around the world every year. "People need to be treated and controlled to reduce that risk of cardiovascular disease, heart attacks and strokes, in the future."

The report, which uses data from the PHRI-led Prospective Urban Rural Epidemiological study, compares how hypertension is treated in countries at different income levels.

Each of the study's roughly 154,000 research subjects had had his or her blood pressure taken and medication use written down. Physicians documented each participant's age, sex and level of education, and examined patients for key risk factors for heart disease.

The data show that people with high blood pressure in a high-income country such as Canada are almost as likely to go under the radar as those in low-income countries, said Chow, who began working with the PHRI while doing post-doctorate work in Hamilton for three years ending in 2009.

Inadequate treatment

Individuals who receive diagnoses in rich countries, she said, are much more likely to receive treatment. The report says this may be a result of poorer access to healthcare and prescription drugs in developing countries.

However, the majority of patients who had begun treatment — including those in rich countries — weren't successfully managing their blood pressure. Some used only one blood pressure drug when the medical literature often advises taking two or more, Chow said.

"When they find out they have high blood pressure, they start out on treatment. That's good, but they have inadequate blood pressure control," she said. "That is really stark universally across all the countries."

At this point, Chow said, researchers "can only speculate" as to why people who have begun treatment don't do a better job of managing their hypertension.

"We definitely know the treatments, we've got the medications, but people aren't on them, and this is the gap that needs to be addressed," she said. "And I think this is the question that we will all be trying to address in the future."