Hypertension can lead to cardiovascular diseases and other chronic conditions. While the impact of hypertension on premature death and life expectancy has been published, the impact on health-adjusted life expectancy has not, and constitutes the research objective of this study. Health-adjusted life expectancy (HALE) is the number of expected years of life equivalent to years lived in full health. Data were obtained from the Canadian Chronic Disease Surveillance System (mortality data 2004–2006) and the Canadian Community Health Survey (Health Utilities Index data 2000–2005) for people with and without hypertension. Life table analysis was applied to calculate life expectancy and health-adjusted life expectancy and their confidence intervals. Our results show that for Canadians 20 years of age, without hypertension, life expectancy is 65.4 years and 61.0 years, for females and males, respectively. HALE is 55.0 years and 52.8 years for the two sexes at age 20; and 24.7 years and 22.9 years at age 55. For Canadians with hypertension, HALE is only 48.9 years and 47.1 years for the two sexes at age 20; and 22.7 years and 20.2 years at age 55. Hypertension is associated with a significant loss in health-adjusted life expectancy compared to life expectancy.
Hypertension or high blood pressure (HTN) is an important risk factor for cardiovascular disease. In 2002, the World Health Organization estimated that at least 50% of cases with cardiovascular disease and 75% of strokes were caused by elevated blood pressure [
The number of Canadians with hypertension is increasing in Canada. The first report on hypertension from the Canadian Chronic Disease Surveillance System published by Public Health Agency of Canada shows that the age-standardized prevalence of hypertension among the adult population increased by about 7% between 1998 and 2006 and is projected to increase by another 25% by the end of 2012 [
This paper reports results on Health-Adjusted Life Expectancy (HALE). HALE is an indicator that can be used as a summary measure of population health. While LE is the average number of years a person is expected to live, HALE is life expectancy weighted or adjusted for the level of Health Related Quality of Life (HRQOL). It combines morbidity and mortality data in one single indicator of population health and indicates the average time that a person could expect to live in a healthy state. Comparison of disparities in LE and HALE for a population of people with and without hypertension, and evaluation of loss in LE and the proportion of life lived in poor health for these cohorts can provide a comprehensive picture of how hypertension changes the lives of people.
There are few published studies which looked at the impact of hypertension on life expectancy [
Health-adjusted life expectancy is a composite indicator that combines morbidity and mortality into a single statistic. Mortality data files from the Canadian Chronic Disease Surveillance System (CCDSS) were used for estimating age and sex-specific mortality rates. While mortality data and population counts are sufficient for calculating life expectancy, a measure of health-related quality of life is also needed to estimate health-adjusted life expectancy, its variance and corresponding 95% confidence intervals. The measure used in this analysis was the Health Utilities Index Mark 3 which was estimated from the Canadian Community Health Survey (CCHS).
The Canadian Chronic Disease Surveillance System is a collaborative network of provincial and territorial chronic disease surveillance systems, supported by the Public Health Agency of Canada [
In each province and territory, the health insurance registry database is linked to the physician billing and hospitalization databases to generate summarized data for residents of Canada who have used the Canadian health care system. These summarized data are stored in the CCDSS for routine analysis. If there is sufficient evidence of use due to hypertension, it is assumed that a person had been diagnosed with hypertension. The minimum requirement was at least 1 hospitalization or 2 physician claims over a 2-year period with specific code(s) for hypertension from the International Classification of Diseases (ICD) (ICD-9 codes 401–405; ICD-10 codes I10– I13 and I15). With respect to hypertension, the CCDSS collects data for the adult population only, that is, 20 years old and older.
For Canadian adults with and without hypertension, age-specific mortality rates for all causes are included in the CCDSS. For this study, the age-specific mortality rates for persons with and without adult hypertension were used to calculate life expectancy and health-adjusted life expectancy. The study was limited to persons who are 20 years old and older.
The Canadian Community Health Survey is an ongoing cross-sectional national health survey, conducted by Statistics Canada [
Prior to 2007, data collection occurred every 2 years for a 12-month period. After major changes to the survey design in 2007, data collection now occurs on an ongoing (monthly) basis with annual releases. Data are available for 2000/2001, 2003, 2005, 2007, 2008, and 2009.
The CCHS produces an annual microdata file and a file combining 2 years of data. The survey collection years can also be combined by users to examine subpopulations of rare characteristics. The respondents of the first three cycles of the survey were asked if they have any of 26–30 chronic conditions including hypertension. The survey data include information for persons aged 12 years and older. The survey does not include people who live in institutions or in remote areas. The household-level response rate in 2005 was 84.9%, and the person-level response rate was 92.5% [
As a measure of health-related quality of life, the Health Utilities Index Mark 3 from the following three CCHS data files was used for this study: (1) cycle 1.1 2000/2001 share file [
HUI3 is a multiattribute utility measure that defines health states according to eight attributes (vision, hearing, speech, ambulation, dexterity, emotion, cognition, and pain), with five or six levels ranging from normal to severely limited functioning for each. Single attribute utility scores range from 0.0 (lowest level of functioning) to 1.0 (full functional capacity) [
The overall scores on the HUI3 range from −0.36 (the worst possible HUI3 health state), through 0.0 (death), to 1.0 (perfect health). From a societal perspective, some health states are considered worse than dead, and consequently are assigned negative scores. Differences of 0.03 or more in overall HUI3 scores and 0.05 or more in single-attribute utility scores are considered to be clinically important [
Sex and age-specific HUI averages were estimated from a combined CCHS data file for persons with and without hypertension. The bootstrap methodology [
All three cycles of the CCHS (cycle 1.1 share file, cycle 2.1 subsample, and cycle 3.1 subsample) were combined by the pooled method to increase the sample size and to decrease variation in the estimates [
Mortality data for Quebec and Nunavut were unavailable from the CCDSS, and health utilities index data from the Northwest Territories and Nunavut were unavailable from the 2000/2001 CCHS (cycle 1.1) survey file. Therefore, these jurisdictions were excluded from all analyses.
The Chiang method [
The variance of LE was calculated by the Chiang method. The variance in HALE, for the population without hypertension, was calculated by the Bebbington method [
Figures
Life expectancy (LE) and health adjusted life expectancy (HALE) for females and males, without hypertension, Canada, 2004 to 2006. (Data source: Canadian Community Health Survey Data Files (CCHS) from Statistics Canada, 2000–2005 and Canadian Chronic Disease Surveillance System Data Files (CCDSS) from Public Health Agency of Canada, 2004–2006. Data Files excluded Quebec, Nunavut and Northwest Territories.)
Life expectancy (LE) and health adjusted life expectancy (HALE) for females and males, with hypertension, Canada, 2004 to 2006. (Data source: Canadian community health survey data files (CCHS) from Statistics Canada, 2000–2005 and Canadian Chronic Disease Surveillance System Data Files (CCDSS) from Public Health Agency of Canada, 2004–2006. Data Files excluded Quebec, Nunavut and Northwest Territories.)
Figure
Health utilities index (HUI) for females and males with and without hypertension (HTN), Canada, 2000 to 2005. (Data source: Canadian Community Health Survey Data Files (CCHS) from Statistics Canada, 2000–2005. Dataset for this study excluded Quebec, Nunavut and Northwest Territories.)
The difference in LE between female and male populations with hypertension varies between 2.0 and 5.2 years across age groups, higher than that in the population without hypertension (Table
Difference in life expectancy (LE) and health-adjusted life expectancy (HALE) between females and males with and without hypertension (HTN) for selected ages, Canada, 2004 to 2006. (Dataset for this study excluded Quebec, Nunavut and Northwest Territories.)
LE(F)-LE(M) | HALE(F)-HALE(M) | |
---|---|---|
At age of 20 years | ||
With HTN | 5.2* | 1.8** |
Without HTN | 4.4* | 2.2* |
At age of 55 years | ||
With HTN | 4.2* | 2.5* |
Without HTN | 3.6* | 1.8* |
At age of 85 years | ||
With HTN | 2.0 | 0.9 |
Without HTN | 1.7 | 0.8 |
*Statistically significant (
**Statistically significant (
Table
Life expectancy (LE), health-adjusted life expectancy (HALE) (With 95% Confidence Intervals), and Loss of LE and HALE at selected ages, by hypertension (HTN) status and sex, Canada, 2004 to 2006. (Dataset for this study excluded Quebec, Nunavut and Northwest Territories.)
Sex | Life expectancy measure | Without HTN (I) | With HTN (II) | Loss of life expectancy associated with HTN (I-II) |
---|---|---|---|---|
At age 20 years | ||||
Females | LE | 65.4 (65.3-65.4) | 62.1 (61.9–62.4) | 3.3* |
HALE | 55.0 (54.6–55.3) | 48.9 (48.1–49.7) | 6.1* | |
LE-HALE | 10.4* | 13.2* | ||
(LE-HALE)/LE | 0.16 | 0.21 | ||
Males | LE | 61.0 (61.0-61.0) | 56.9 (56.7–57.2) | 4.1* |
HALE | 52.8 (52.5–53.1) | 47.1 (46.3–47.8) | 5.7* | |
LE-HALE | 8.2* | 9.8* | ||
(LE-HALE)/LE | 0.13 | 0.17 | ||
At age 55 years | ||||
Females | LE | 31.6 (31.6-31.7) | 30.1 (30.1-30.2) | 1.5* |
HALE | 24.7 (24.4–25.1) | 22.7 (22.3–23.0) | 2.0* | |
LE-HALE | 6.9* | 7.4* | ||
(LE-HALE)/LE | 0.22 | 0.25 | ||
Males | LE | 28.0 (28.0-28.1) | 25.9 (25.8-25.9) | 2.1* |
HALE | 22.9 (22.6–23.2) | 20.2 (19.8–20.6) | 2.7* | |
LE-HALE | 5.1* | 5.7* | ||
(LE-HALE)/LE | 0.18 | 0.22 | ||
At age 85 years | ||||
Females | LE | 8.6 | 8.5 | 0.1 |
HALE | 5.2 | 4.9 | 0.3 | |
LE-HALE | 3.4 | 3.6 | ||
(LE-HALE)/LE | 0.40 | 0.42 | ||
Males | LE | 6.9 | 6.5 | 0.4 |
HALE | 4.4 | 4.0 | 0.4 | |
LE-HALE | 2.5 | 2.5 | ||
(LE-HALE)/LE | 0.36 | 0.38 |
*Statistically significant at .05.
In this study LE and HALE were estimated for Canadian adults (20 years old and older) with and without diagnosed hypertension by sex and fourteen 5-year age intervals. Our results show that life expectancy decreases with increasing age and that the decline is faster for LE than HALE (Figures
It was observed that a greater number of years of life were lost in HALE than in LE especially at younger ages (Table
The results attribute significant loss of health expectancy to hypertension. In reality, hypertension is a convenient marker which functions as a surrogate for health risks not controlled for in the analysis. Future work should target controlling for risk factors concurrent with a diagnosis of hypertension. That kind of study could quantify the potential impact of prevention of obesity, smoking, physical inactivity, and other risk factors associated with population health. More detailed data would be required. For instance mortality rates by BMI class would be required to evaluate the effect obesity on population health. Work plans have been prepared to explore the feasibility of controlling for obesity in HALE estimation.
The absolute difference between LE and HALE represents the number of years a person spends in poor health. Relative differences between LE and HALE quantify the portion of life a person spends in poor health. That is, the ratio of unhealthy years to the life expectancy ((LE-HALE)/LE). These measures are only meaningful within the same population (i.e., for the population of people of the same age with or without hypertension). Both measures were greater for populations of people with hypertension than for people without the disease (Table
Differences in LE associated with hypertension were estimated for people in eastern Finland using a baseline age of 25 years by Kiiskinen et al. [
A limitation of our study was that data for residents of long-term care facilities were not available for calculation of our estimates of life expectancy and health-adjusted life expectancy. As a result, the true values for the entire population would be somewhat lower than what we reported. It is also important to note that misclassification of hypertension status is present in both the survey data and the surveillance system data we used. In the Canadian Community Health Survey, misclassification can be due to self-reporting bias, a tendency to underreport the true disease status. In the Canadian Chronic Disease Surveillance System, misclassification can be present in geographic areas where complete data are not available. Areas with a larger proportion of salaried physicians provide the least complete data, which results in identifying fewer individuals with disease. Consequently, the disease status concordance between the two data sources varies by province and territory [
This paper described the method used by the Public Health Agency of Canada to calculate life expectancy and health-adjusted life expectancy among Canadian adults with and without hypertension, based on mortality data for 2004 to 2006 and morbidity data for 2000 to 2005. Our work shows that it is possible to calculate health-adjusted life expectancy for all Canadians and for subpopulations with this particular chronic condition. Our method can be adapted for calculations for other chronic conditions and diseases to provide useful information for public health researchers and policy makers.