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Blood pressure and hypertension

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by Jason DeGuire, Janine Clarke, Kaitlyn Rouleau, Joel Roy, and Tracey Bushnik

DOI: https://www.doi.org/10.25318/82-003-x201900200002

Hypertension, or high blood pressure, is a leading contributor to disability-adjusted life years.^{Note 1} Canada’s reported rates of hypertension awareness, treatment and control are some of the highest in the world.^{Note 2} This has been attributed to several factors, including the efforts of health care organizations and professionals to reduce the burden of hypertension, and the efficacy of knowledge translation about hypertension and its risks.^{Note 3} Despite these efforts, hypertension affected almost 1 in 4 Canadian adults in 2012-2015^{Note 4} and is currently ranked as the leading risk factor for death globally^{Note 5}. In 2010, the costs attributable to hypertension in Canada were estimated at $13.9 billion, and are forecasted to increase to $20.5 billion by 2020.^{Note 6} Ongoing surveillance is necessary to monitor and assess the population burden of hypertension in Canada.

Using the most recent data (2012-2015) from the Canadian Health Measures Survey (CHMS), this study examines systolic blood pressure (SBP), diastolic blood pressure (DBP), and hypertension prevalence, awareness, treatment and control estimates for adults aged 20 to 79 by age group and sex. Hypertension is defined using two sets of blood pressure thresholds: SBP>=140 mm Hg or DBP>=90 mm Hg;^{Note 7} and SBP>=130 mm Hg or DBP>=80 mm Hg (as per American College of Cardiology (ACC) and American Heart Association (AHA) 2017 guidelines.^{Note 8} To assess trends over time, crude and age-standardized estimates of SBP, DBP, and hypertension prevalence, awareness, treatment and control are also presented for adults aged 20 to 79 in 2007-2009, 2009-2011, 2012-2013 and 2014-2015.

Methods

Data source

The data are from the CHMS, a nationally representative health survey. The CHMS covers 96% of the Canadian population aged 3 to 79. It excludes people living in the territories, people living on reserves and in other Aboriginal settlements, full-time members of the Canadian Forces, institutionalized individuals, and residents of certain remote areas.^{Note 9Note 10}

Data collection takes place in two parts: at an in-person interview in the home, where information is collected on health-related risk factors, health conditions and medication use; and a subsequent visit to a mobile examination centre (MEC), where direct physical measurements, including blood pressure, are taken (www.statcan.gc.ca/chms). To produce estimates by sex and age group for the 2012-2015 reference period, cycles 3 (2012-2013) and 4 (2014-2015) were combined, for a total of 6,357 adults aged 20 to 79. Pregnant women (n = 43) and those with incomplete blood pressure data (n = 20) were excluded. The final analytical sample size was 6,294.

For comparisons over time, results based on the same exclusion criteria are also presented for each individual survey cycle. The final sample was 3,487 in cycle 1 (2007-2009), 3,618 in cycle 2 (2009-2011), 3,158 in cycle 3 (2012-2013), and 3,136 in cycle 4 (2014-2015).^{Note 9Note 10Note 11Note 12}

Measures and definitions

Blood pressure.SBP and DBP measurements using the BpTRU^TM BPM-300 (BpTRU Medical Devices Ltd., Coquitlam, British Columbia) were taken at the MEC. The mid-arm circumference was measured for cuff placement, and the appropriate cuff size was used. The device takes six readings for each participant, and the last five are averaged to determine SBP and DBP levels.^{Note 13}

Hypertensive_140/90.Respondents were considered hypertensive if SBP >= 140 mm Hg or DBP >= 90 mm Hg or if they reported antihypertensive medication use in the past month.

Hypertensive_130/80.Respondents were considered hypertensive if SBP >= 130 mm Hg or DBP >= 80 mm Hg or if they reported antihypertensive medication use in the past month.

Isolated systolic hypertension is defined as the proportion of people with hypertension who have measured SBP ≥ 140 mm Hg and measured DBP < 90 mm Hg.

Awareness (of hypertension) was defined as a hypertensive_140/90 respondent’s report of either diagnosed hypertension or antihypertensive medication use in the past month.

Treatment (of hypertension) was defined as a hypertensive_140/90 respondent’s report of antihypertensive medication use in the past month.

Controlled (hypertension) was defined as a hypertensive_140/90 respondent’s report of antihypertensive medication use in the past month together with a measured mean SBP < 140 mm Hg and DBP < 90 mm Hg.

Antihypertensive medication use refers to the medications recorded during the household and clinic interviews assigned to the following Anatomical Therapeutic Classification (ATC) codes: C02 (excluding C02KX01); C03 (excluding C03BA08 and C03CA01); C07 (excluding C07AA07, C07AA12 and C07AG02); C08; and C09.

Age-standardized prevalence represents the potential prevalence of hypertension if the study population had had the same age distribution as a given standard population. Age standardization allows for comparisons of estimates by removing the influence of changes in the age distribution of the population.

Analysis

Weighted estimates of mean SBP and DBP, and the prevalence of hypertension, hypertension awareness, treatment and control were calculated. Replicate weights generated by Statistics Canada were used to calculate variance estimation (95% confidence interval [CI]) and conduct significance testing. The appropriate survey weights and denominator degrees of freedom were used to analyze the combined or individual cycles of data.^{Note 9Note 10Note 11Note 12Note 14} The data were analyzed with SAS 9.3 and SUDAAN 11.0.

All estimates are presented as per the suggested standards of uniform reporting (crude, age-standardized, by age group) of hypertension in adults using population survey data.^{Note 7} The direct method was used to age-standardize estimates to the World Health Organization’s world standard population.^{Note 15}

Results

Average systolic and diastolic blood pressure

Average SBP/DBP was 115/74 mm Hg in males aged 20 to 79 in 2012-2015 and 112/70 mm Hg in females aged 20 to 79 in the same period (Table 1). SBP and DBP varied by age group and sex. For both males and females, SBP increased with age, but the difference in SBP between the youngest and oldest age groups was much greater among females (25 mm Hg) than among males (14 mm Hg). Mean DBP was highest for middle-aged males (40 to 69 years) whereas females’ mean DBP was fairly stable across all age groups. Neither the crude nor the age-standardized average SBP and DBP values for males and females changed significantly from 2007-2009 to 2012-2015 (Table 2). In 2012-2015, the prevalence of isolated systolic hypertension (ISH) was higher among females than among males (Figure 1). Males and females aged 70 to 79 had a higher prevalence of ISH than younger age groups.

Hypertension prevalence

In 2012-2015, nearly 1 in 4 males (24%) and females (23%) aged 20 to 79 had hypertension_140/90 (Table 3). The prevalence of hypertension_140/90 increased significantly with age. Males (71%) and females (69%) aged 70 to 79 were about three times as likely to be categorized as hypertensive_140/90 as males (25%) and females (21%) aged 40 to 59. From 2007-2009 to 2012-2015, the prevalence of hypertension_140/90 among 20- to 79-year-olds remained fairly stable, at about 23% (crude) or 18% (age-standardized) (Table 2).

Applying the 130/80 mm Hg threshold (hypertension_130/80) to categorize people as hypertensive^{Note 8} resulted in a significant increase in the overall prevalence of hypertension among both sexes and all age groups (Figure 2). Specifically, 40% of males had hypertension_130/80; this is 16 percentage points higher than the prevalence of hypertension_140/90. Among females, the prevalence of hypertension_130/80 was nine percentage points higher than the prevalence of hypertension_140/90. The largest relative difference in prevalence was observed among those aged 20 to 39 (3% to 15%, sexes combined).

Hypertension awareness, treatment and control

Eighty-four percent of those aged 20 to 79 with hypertension_140/90 were aware of their condition (Table 3). However, people aged 20 to 39 were much less likely to be aware of being hypertensive_140/90 (65%) than those in the older age groups. About 80% of those aged 20 to 79 with hypertension_140/90 reported being treated for their condition, and 66% of those with hypertension_140/90 had their hypertension_140/90 controlled (Table 3). As was the case with awareness, those in the youngest age group were less likely to be treated (55%) or to have their hypertension_140/90 controlled (51%). There was little difference between males and females in the overall crude estimates of awareness, treatment and control (Table 3), and little change from 2007-2009 to 2014-2015 (Table 2).

Discussion

This study found that, in the period from 2012 to 2015, nearly 1 in 4 Canadian males and females aged 20 to 79 had hypertension_140/90, when defined as measured BP higher than 140/90 mm Hg or past-month use of anti-hypertensive medication. Though measurement variation across devices makes direct comparisons difficult,^{Note 16Note 17Note 18} these rates are lower than those reported in other high-income countries where BP was also measured using an automated device.^{Note 19} The present study also found that the crude and age-standardized prevalence of hypertension_140/90 remained fairly stable from 2007-2009 to 2014-2015, a finding consistent with recent results from the United States.^{Note 20}

This study also found that people aged 70 to 79, particularly women, were much more likely to have isolated systolic hypertension (ISH) than other age groups. ISH among older people is relatively common,^{Note 21} and is due to reduced elasticity of large arteries, long-term build-up of plaque, and increased incidence of cardiac and vascular disease.^{Note 22} Some studies suggest that higher prevalence among older women than among older men may be related to the hormonal changes that occur during menopause.^{Note 23}

Recently, the ACC/AHA Task Force on Clinical Practice Guidelines recommended a new, lower threshold of 130/80 mm Hg for hypertension,^{Note 8} further to evidence suggesting a gradient of increased cardiovascular disease risk for SBP and DBP levels above 120/80 mm Hg. Applying this revised threshold to the study population increased the overall prevalence of hypertension, with the largest relative increase observed among those aged 20 to 39. Also, 2011 to 2014 data from the National Health and Nutrition Examination Survey (NHANES) in the United States showed that the youngest age group (20 to 44) had the greatest increase in hypertension prevalence after application of the new threshold.^{Note 8}

Diagnosis and awareness of hypertension are essential to manage and control blood pressure.^{Note 24} This study found that just over 4 out of 5 people with hypertension_140/90 were aware of their condition. This rate was fairly stable from 2007-2009 to 2014-2015, and remained significantly higher than the prevalence of awareness reported in other high-income countries during this period.^{Note 19} However, the results also show that those aged 20 to 39 were much less likely to be aware of being hypertensive_140/90 than people in the older age groups. This lack of awareness among younger people has been reported in the United States^{Note 24} and elsewhere,^{Note 25Note 26} and highlights the importance of initiatives that encourage this population to get their blood pressure checked.^{Note 27}

As was the case for awareness, this study found that rates of treatment and control did not change significantly in Canada from 2007-2009 to 2014-2015. In general, treatment rates in Canada were considerably higher than those reported in other high-income countries.^{Note 19} Hypertension_140/90 control rates were also higher in Canada than in other countries,^{Note 19} particularly the United States, where less than half of those with hypertension_140/90 had measured BP lower than 140/90 mm Hg.^{Note 20} Canada’s high rates of awareness, treatment and control have been attributed to several factors, including the concerted efforts of health care organizations and professionals to reduce the burden of hypertension, and effective knowledge translation about hypertension and its risks^{Note 3}. However, this study found that treatment and control rates were lower among the youngest age group, particularly among males. The lower rates for younger people could be associated with their fewer interactions with the health care system.^{Note 28} This suggests that initiatives encouraging blood pressure assessment for this population may be more appropriate outside formal health care channels.^{Note 29}

This study has several strengths. The CHMS is a population-based study with a large sample size, and blood pressure was measured objectively using an automated device with high quality control. However, the CHMS response rate for each cycle was from 52% to 55%. Although applying survey weights helps to ensure that the sample is representative of the target population, bias might exist if non-respondents differed systematically from respondents.

Conclusion

This report provides an update on measured SBP, DBP, and hypertension prevalence, awareness, treatment and control in Canada. From 2007-2009 to 2012-2015, blood pressure levels and hypertension_140/90 prevalence remained stable among Canadian adults aged 20 to 79. Isolated systolic hypertension is approximately twice as prevalent among females as among males. Applying a new, lower BP threshold increased hypertension prevalence significantly among both males and females aged 20 to 79. While Canadians in general had high levels of awareness, treatment and control of hypertension_140/90, this analysis highlighted that younger males are less likely to be aware of their hypertension_140/90 and less likely to be treated and controlled. Ongoing surveillance of blood pressure in Canada is necessary to accurately quantify the population burden of hypertension and to identify population groups that may be at higher risk of adverse outcomes.

Acknowledgement

The authors thank Deirdre Hennessy for her expert advice throughout the research process.