Jennifer Patry-Parisien, of Statistics Canada, demonstrates a blood pressure test on Josee Savoie at a mobile examination centre in Laval, Que., in January 2009. (Graham Hughes/Canadian Press)

Nearly one in five Canadians adults — about 4.6 million people between the ages of 20 and 79 — has high blood pressure, Statistics Canada reported Wednesday.

The study was based on automated measurements of blood pressure and self-reported use of blood pressure medication, the department said in its publication Health Reports.

When blood pressure is too high, it puts stress on the body's entire vascular system, forcing the heart to work harder, and increasing the risk of death from a variety of causes including heart disease and stroke.

As part of the broader Canadian Health Measures Survey, researchers surveyed and tested 5,600 Canadians aged six to 79 years between March 2007 and February 2009 at mobile examination centres.

Participants were classified as having hypertension or high blood pressure if their systolic pressure, the top number, was 140 or higher, their diastolic pressure, or bottom number, was 90 or higher, or they reported they had used medication for high blood pressure in the past month.

Uncontrolled blood pressure

Another 20 per cent of participants 20 to 79 years old were in the pre-hypertension range, and 61 per cent had normal blood pressure.

The pre-hypertension range was defined according to internationally recognized standards: systolic blood pressure of 120 to 139 or diastolic blood pressure of 80 to 89. Pre-hypertension is linked to an increased risk of cardiovascular disease and is strongly predictive of hypertension.

About 80 per cent of the 4.6 million adults with hypertension were being treated with drugs, the report's authors found.

In two-thirds of those with hypertension, blood pressure was controlled with medication.

Age factor

But in about 6.6 per cent of the adult population, the condition was uncontrolled, meaning that their blood pressure stayed in the hypertensive range.

The prevalence of hypertension went up with age:

• Ages 20 to 39: two per cent.
• Ages 40 to 59: 19 per cent.
• Ages 60 to 79: 53 per cent.

"Twenty years ago, we did a survey involving measured blood pressure, and at that time only 13 per cent of people with hypertension had their blood pressure in the range we call controlled," said Kathryn Wilkins, a senior analyst at Statistics Canada in Ottawa who led the study. "This compares with 66 per cent today. So that's encouraging."

It's difficult to say why, Wilkins said, but campaigns to promote awareness of the importance of hypertension as a risk factor for heart disease and stroke may be paying off. Machines to measure blood pressure are more common in pharmacies, and awareness by physicians has also improved, she said.

"The awareness levels have really come up," agreed Laura Weyland, a pharmacist and owner of a Shoppers Drug Mart in Toronto. "I think a lot of doctors' offices are recommending to go to the drug store and check your blood pressure. Or if [people] realize that their parents have high blood pressure, they come in and they can check it, and make sure it is within the normal range."

Healthier lifestyles

Overall, the prevalence of hypertension was nearly the same in both sexes, at 19.7 per cent in men and 19 per cent in women.

But in older Canadians, there was a gap in blood control between men and women. For example, of those aged 60 to 69 using anti-hypertensive drugs, 19 per cent of women had uncontrolled blood pressure compared with seven per cent of men.

"Women are more likely to be aware of their hypertension, they're more likely to be on medication than men with hypertension. But somehow the success, or the efficacy, of the medication seems to be lower in women than in men," Wilkins said.

"And this has been observed in other countries as well, and the reasons really are not understood at this point."

Nearly 67 per cent of Canadians over age 60 needed medication to control their hypertension.

"The sad reflection is that this could've been achieved by other mechanisms [than medication], such as reducing the amount of salt we eat, eating a healthier diet, staying physically active, and staying a good body weight," said study co-author Dr. Norman Campbell of the University of Calgary.

Canadians who don't have high blood pressure yet probably will in the future, Campbell said, citing research that shows that nine out of ten people who live a normal life span will eventually end up with hypertension.

The Canadian Health Measures Survey also used direct measurements of fitness and activity levels, nutritional status, exposure to environmental contaminants, infectious disease status, oral health, lung capacity and heart rate.

Blood pressure in children was not measured.

With files from The Canadian Press