Association between Physical Inactivity and Health-Related Quality of Life in Adults with Coronary Heart Disease

Abstract

Background:

Health-Related Quality of Life (HRQoL) provides an accurate measure of the health status of coronary heart disease (CHD) patients. However, few studies have examined the relationship between physical inactivity and HRQoL in CHD survivors. We evaluated this association in a cross-sectional study of 21,936 CHD participants of the 2015 Behavioral Risk Factor Surveillance System.

Methods:

CHD diagnosis, HRQOL and Physical Activity were self-reported. Physical activity (PA) was categorized (1) based on intensity into no PA, light to moderate PA and vigorous PA, and (2) based on duration and frequency into no PA, insufficiently active and active. HRQoL was assessed by the CDC HRQoL questionnaire. Participants with 14+ physical or mental unhealthy days in a 30-day window were grouped into poor physical or mental HRQoL. We estimated the odd ratios (AOR) and 95% confidence intervals (CI) of poor HRQoL associated with PA after adjusting for age, sex, education, income level, social support, smoking status, ethnicity/race, BMI, chronic conditions, and CHD groups.

Results:

Compared to vigorous PA, adults with no PA had higher odds (95% CI) of poor physical HRQoL [1.82 (1.58, 2.10)] and poor mental HRQoL [1.28 (1.05, 1.55)]. When compared to active adults, AOR (95% CI) for adults with no PA were 1.80 (1.55, 2.01) and 1.17 (0.97, 1.42) for poor physical and mental HRQoL, respectively.

Conclusions:

We found an association between physical inactivity and poor physical and mental HRQoL among CHD survivors. There is a need for longitudinal studies to determine the temporality of this association.

1.0. INTRODUCTION

Coronary heart disease (CHD) is a major cause of death worldwide.¹ It is characterized by cholesterol-containing deposits in the major heart blood vessels, which results in angina, shortness of breath, fatigue and myocardial infarction.² The number of survivors is growing due to an aging population, and advancement in CHD treatment and management.^3,4 Most of the research on survivorship has focused on morbidity and mortality, however there is increasing awareness that quality of life (QoL) is also an important health indicator.^5,6 The World Health Organization defines QoL as “a broad ranging concept affected in a complex way by the person’s physical health, psychological state, personal beliefs, social relationships.”⁷ Since living with CHD is complex, it is important to assess how the disease and its symptoms impact overall health.⁸

One of the constructs used to measure QoL is health-related quality of life (HRQoL). HRQoL specifically measures diseases’ impact on health.⁵ This study uses a HRQoL tool developed by the Centers of Disease Control and Prevention (CDC).⁹ There is ample evidence suggesting that HRQoL is a strong indicator of CHD patients’ health.^10–14 It can predict subsequent mortality, independent of other health indicators such as hypertension and smoking status.^15–17 Awareness of HRQoL could serve as a motivational tool to promote adoption of healthy behaviors and provide new insights into CHD outcomes.^18–20

CHD survivors have worse mental and physical HRQoL compared to the general population.²¹ In CHD patients, HRQoL has been associated with medication adherence, self-care, social support, controlled cholesterol, blood pressure, smoking cessation, and weight loss.^22–25 HRQoL is impaired by having one or more risk factors, stress, depression and anxiety.^22–25 However, despite the extensive characterization of HRQoL predictors, very few studies have investigated the independent association between sedentary lifestyle and HRQoL among cardiovascular disease patients.^26–29 A decrease in sedentary time has been associated with improved HRQoL in patients undergoing cardiac rehabilitation,^27–29 although no such association was found in congestive heart failure patients.²⁶

Sedentary lifestyle, or physical inactivity, is used to identify people who do not meet recommended levels of physical activity (PA).³⁰ The PA guidelines for Americans recommend that adults obtain at least 150 minutes a week of moderate-intensity aerobic PA, or vigorous-intensity equivalent.³¹ Guidelines for the secondary prevention of CHD and other atherosclerotic vascular disease recommend a similar PA level.^32,33 However, CHD patients tend to engage less in physical activities, especially moderate and vigorous-intensity PA.³⁴

Thus, to improve our understanding of PA and QoL in adults with cardiovascular disease, we examined the association between physical inactivity and HRQoL in 21,936 adults with CHD from the 2015 Behavioral Risk Factor Surveillance System (BRFSS). We hypothesized that physical inactivity is associated with poor mental HRQoL and poor physical HRQoL among those with CHD.

2.0. METHODS

2.1. Study Population

BRFSS is a state-based phone surveillance system overseen by CDC. BRFSS collects data from non-institutionalized U.S. adults aged 18 and older on many lifestyle and behavioral factors that place them at risk for chronic diseases. It uses an independent probability sample of U.S. households with landline and cell phones. In 2015, the response rate was 48.2% for landlines and 47.2% for cell phones.³⁵

2.2. Coronary heart disease (CHD)

Persons with CHD were defined as those who answered “Yes” to the question: “Has a doctor, nurse or other health professional ever told you that you had angina or coronary heart disease?” We divided them into three groups – myocardial infarction (MI), no MI but difficulty walking, and no MI nor difficulty walking - based on their responses to the questions: “Has a doctor, nurse or other health professional ever told you that you had a heart attack, also called a myocardial infarction?” or “Do you have serious difficulty walking or climbing stairs?” The latter question was included because both the Canadian Cardiovascular Society and Rose Chest Pain Questionnaire use how walking and managing stairs impact CHD to grade severity.^{56, 57} There is also a moderate to strong correlation between self-reported and physician diagnosed CHD.^36–38

2.3. Physical inactivity (no PA)

In this analysis, physical inactivity was treated as the independent variable. Respondents were asked, “During the past month, other than your regular job, did you participate in any physical activities or exercises such as running, calisthenics, golf, gardening, or walking for exercise?” and “What type of physical activity or exercise did you spend the most time doing during the past month?”. Respondents answering “Yes” to these questions were then asked about “How many times per week or per month did you take part in this activity during the past month?” and “And when you took part in this activity, for how many minutes or hours did you usually keep at it?” These questions have reasonable reliability and validity (moderate activity k = 0.35 - 0.53; vigorous activity k = 0.80-0.86).^37,39 BRFSS assigned a metabolic equivalent (MET) value to each reported activity. Vigorous PA was defined as MET values >= 60% of the age and sex-specific maximal oxygen uptake. Activity with MET values >= 3, but not vigorous, was rated moderate. All other physical activities that were not moderate or vigorous were rated as light.

We used two approaches to categorize PA. The first categorization (Definition 1) was based on intensity and included three levels: no PA, light to moderate intensity PA (LMPA), and vigorous intensity PA (VIPA). We combined light and moderate intensity to form a LMPA category because only a handful of participants (n=68) were engaged in light PA. Organizing this category is clinically reasonable bcause light activity may produce marked health benefits among individuals with CHD.⁴⁵ The second categorization (Definition 2) was based on duration and frequency, and included three groups: no PA, insufficiently active (0–149 min/week) and active (>150 min/week of moderate-intensity activities, or vigorous equivalent.)

2.4. Health-Related Quality of Life (HRQoL)

HRQoL was the dependent variable. Based on the CDC HRQoL questions, we developed two indicators: (1) physical HRQoL (“how many days during the past 30 days was your physical health not good?”) and (2) mental HRQoL (“how many days during the past 30 days was your mental health not good?”).⁴⁰ The questions have moderate to excellent reliability (physical health ICC = 0.67 – 0.74; mental health ICC = 0.63 – 0.71).^37,40–43 We dichotomized physical and mental HRQoL into two groups depending on whether respondents reported 14+ unhealthy days. The demarcation point of 14 days is considered by clinicians and researchers as a meaningful cut point for substantially impaired HRQoL and has been previously used in other studies.^19,44

2.5. Covariates

We controlled for covariates that have been associated with HRQoL and physical inactivity in this or previous studies: age, sex, income level, education, smoking status, race, BMI, CHD groups and number of chronic conditions.^13,19,44,45 We categorized participants into having zero, one, two, or 3+ chronic conditions based on self-reported physician diagnoses of stroke, cancer, heart attack, asthma, COPD, arthritis, depression, kidney disease, and diabetes. Age was a 14-level categorical variable in the BRFSS. Since CHD occurs predominantly in the older population, age was categorized into 18-60, 60-69, 70-79, >=80 years. Income was categorized into <=$25,000; $25,000 to $50,000; >$50,000. Smoking status was categorized into current, former and never based on respondents’ response to smoking in the last twelve months. A non-respondent category was created for missing values of covariates.

2.6. Analytical sample

In 2015, 441,456 adults were surveyed. 416,166 participants with no CHD were excluded. Of the remaining, 3,354 were excluded for missing data pertaining to PA (n=2,117) and HRQOL (n= 1,237). The final analytical sample included 21,936 adults.

2.7. Statistical Analysis

Statistical analysis was performed using SAS version 9.4. P values < 0.05 (two-sided) were considered significant. The distribution of patients’ characteristics across PA groups were characterized using proportions (Pearson’s chi-square test) for categorical variables and means (standard deviations) for continuous variables. We used logistic regression to estimate the odds ratios (OR) and 95% confidence intervals (95% CI) for poor physical and mental HRQoL associated with physical inactivity.

We used four models to examine the association between physical inactivity and HRQoL. Model 1 was unadjusted. Model 2 was adjusted for age, sex and race (non-modifiable risk factors). Model 3 was additionally adjusted for income, smoking status, BMI, social support, education and the number of chronic conditions (modifiable risk factors.) Model 4 was further adjusted for CHD groups. We then explored whether the association differed by CHD groups, age, sex, education and income by adding interaction terms to Model 4. We used a Wald Test and P values < 0.1 (two-sided) were considered significant for the interactions.

To account for survey design, we weighted the data using weights provided by BRFSS.⁴⁶ We also accounted for clustering by using primary sampling units.

3.0. RESULTS

Among the 21,936 CHD adults, 66.6% were aged 65 years and older, 41.5% were female and 73.2% were non-Hispanic white. Furthermore, 16.7% were current smokers, 38.3% had BMI > 30.0 kg/m² and 48.7% had 3+ chronic conditions. The characteristics of respondents stratified by PA intensity (Definition 1) are presented in Table 1. For PA definition 1, 38.2% reported no PA, 21.6% reported LMPA and 40.2% reported VIPA. For PA definition 2, 45.0% reported being active (mean minutes (SD) of activity per week was 741.4 (869.6)), 16.8% reported insufficiently active (mean minutes (SD) of activity per week was 69.6 (45.6)), and 38.2% reported no PA. There was a noticeable overlap between the definitions of physical activity. Among all VIPA participants, 83.6% were active and 16.4 % had insufficient activity; while of the LMPA participants, 52. 3% were active, and 47.7% had insufficient activity (Supplemental Table 3). Respondents with no PA tended to have lower income, MI, difficulty walking, and multiple chronic diseases compared to VIPA ((Table 1; p-values < 0.01.)

Table 1:

Weighted characteristics of adults with CHD by intensity of physical activity (2015 BRFSS)

	No PA	Light to Moderate PA (LMPA)	Vigorous PA (VIPA)
	(n = 8,353, 38.1%)	(n = 4,736, 21.6%)	(n=8,847, 40.2%)	P-value
Women	4,509 (47.6%)	2,056 (38.3%)	3,557 (37.3%)	<0.01
Age, years				<0.01
18-59	1,700 (30.5%)	1,902 (52.2%)	745 (12.5%)
60-69	2,421 (28.6%)	2,206 (38.5%)	2,004 (22.5%)
70-79	2,405 (24.2%)	612 (9.2%)	3,569 (39.6%)
>= 80	1,772 (16.0%)	16 (0.2%)	2,529 (25.4%)
missing	55 (0.1%)	-	-
Race				<0.01
White, non-Hispanic	6,537 (70.0%)	3,655 (67.7%)	7,681 (81.1%)
Black, non-Hispanic	676 (11.8%)	384 (11.2%)	398 (6.7%)
Hispanic	555 (11.4%)	336 (13.4%)	284 (5.6%)
Other, non-Hispanic	452 (5.3%)	301 (6.8%)	361 (5.4%)
missing	133 (1.5%)	60 (1.0%)	123 (1.2%)
Education				<0.01
Less than high school	1,254 (25.5%)	478 (19.0%)	643 (13.2%)
High school	3,035 (33.3%)	1,444 (30.5%)	2,366 (27.2%)
Some college	2,363 (28.7%)	1,379 (31.5%)	2,426 (31.7%)
College or more	1,674 (12.4%)	1,426 (18.8%)	3,393 (27.8%)
missing	27 (0.2%)	9 (0.2%)	19 (0.2%)
Income, dollars				<0.01
<25,0000	3,364 (39.7%)	1,607 (35.1%)	2,092 (22.7%)
25,000 to 50,000	1,949 (24.4%)	991 (21.6%)	2,277 (26.2%)
>50,000	1,554 (19.7%)	1,542 (30.8%)	3,129 (36.1%)
missing	1,486 (16.2%)	596 (12.5%)	1,349 (15.0%)
Smoker				<0.01
Current	1,593 (21.4%)	915 (21.4%)	648 (7.96%)
Former	3,675 (42.5%)	2,029 (40.3%)	4,312 (49.4%)
Never	3,036 (35.5%)	1,772 (37.7%)	3,831 (41.9%)
missing	49 (0.6%)	20 (0.6%)	56 (0.7%)
BMI (kg/m2)				<0.01
≤ 25.0	1,693 (20.7%)	947 (18.1%)	2,465 (28.5%)
25.0 - 30.0	2,675 (30.3%)	1,629 (36.6%)	3,642 (39.7%)
≥ 30.0	3,627 (44.8%)	1,985 (41.5%)	2,511 (28.6%)
missing	358 (4.21%)	175 (3.8%)	229 (3.2%)
CHD groups				<0.01
Has MI	4,165 (51.4%)	2,225 (44.4%)	4,048 (44.8%)
No MI, diff walking	2,441 (28.1%)	875 (19.1%)	1,353 (16.1%)
No MI, No diff walking	1,747 (20.5%)	1,636 (36.5%)	3,446 (39.1%)
Chronic Conditions				<0.01
0	387 (5.32%)	436 (11.3%)	845 (9.31%)
1	1,199 (13.6%)	984 (22.7%)	2,154 (24.9%)
2	1,807 (20.6%)	1,119 (23.2%)	2,323 (26.7%)
3+	4,960 (60.5%)	2,197 (42.8%)	3,525 (39.1%)

Note: Data are reported as N (weighted percent)

Abbreviations: PA – physical activity; CHD - coronary heart disease; diff walking - difficulty walking; MI - myocardial infarction

Thirty three percent of the participants had poor physical HRQoL. The mean (SD) number of physically unhealthy days was 25.9 (6.1). 16.2% of respondents had poor mental HRQoL. The mean (SD) number of mentally unhealthy days was 24.8 (6.4). There was a low-to-moderate correlation between physical and mental HRQoLs (Pearson correlation coefficient was 0.37, p-value < 0.01).

3.1. Association between PA (Definition 1) and physical HRQoL

In all four models, there was a significant association between poor physical health and no PA (p-value < 0.001). In the fully adjusted model (Model 4), compared to VIPA, the OR (95% CI) for poor HRQoL was 1.82 (1.58, 2.10) for no PA and 1.22 (1.02, 1.46) for LMPA (Table 2). Furthermore, the OR (95% CI) for poor HRQoL was 1.49 (1.26, 1.77) for no PA versus LMPA (data not presented in the tables). We also found the association did not significantly differ by CHD groups, race, income, age or education [p_{for interaction} > 0.10] (Supplemental Table 1).

Table 2:

Weighted analysis of the likelihood of having poor HRQoL^a among different levels of physical activity based on intensity

	No. with poor HRQoL/ No. of participants	Model Ib OR (95% CI)	Model IIc OR (95% CI)	Model IIId OR (95% CI)	Model IVe OR (95% CI)
Physical Health
VIPA	1904/8847	1 (ref)	1 (ref)	1 (ref)	1 (ref)
LMPA	1507/4736	1.67 (1.43, 1.96)	1.36 (1.15, 1.60)	1.24 (1.04, 1.48)	1.22 (1.02, 1.46)
No PA	3900/8353	3.09 (2.72, 3.50)	2.79 (2.45,3.18)	1.97 (1.72, 2.59)	1.82 (1.58, 2.10)
p-value		< 0.001	< 0.001	< 0.001	< 0.001
Mental Health
VIPA	777/8847	1 (ref)	1 (ref)	1 (ref)	1 (ref)
LMPA	926/4736	2.37 (1.93, 2.91)	1.31 (1.06, 1.63)	1.16 (0.92, 1.46)	1.15 (0.91, 1.44)
No PA	1848/8353	2.69 (2.27, 3.17)	2.00 (1.67, 2.39)	1.34 (1.11, 1.62)	1.28 (1.05, 1.55)
p-value		< 0.001	< 0.001	0.010	0.044

Abbreviations: HRQoL – health related quality of life; No PA -no physical activity, LMPA - light to moderate physical activity; VIPA - vigorous physical activity; OR -odds ratio; CI – confidence interval; ref – reference group

^aPoor HRQoL is defined as having 14 or more physical or mental unhealthy days

^bModel I: unadjusted model

^cModel II: adjusted for age, sex, race

^dModel III: adjusted for age, sex, race, education, income, smoking status, BMI, and number of chronic conditions

^eModel IV: adjusted for age, sex, race, education, income, smoking status, BMI, number of chronic conditions and CHD groups.

3.2. Association between PA (Definition 1) and mental HRQoL

We found a significant association between poor mental health and no PA (p-value < 0.05, Table 2). In Model 4, compared to VIPA, the OR (95% CI) for poor HRQoL was 1.28 (1.05, 1.55) for no PA and 1.15 (0.91, 1.44) for LMPA. This association did not significantly differ by CHD groups, race, income or age [p_{for interaction} > 0.10] (Supplemental Table 1). However, the association differed by education (p_{for interaction} = 0.004). It was stronger among those who graduated college [1.57 (1.11, 2.21)], high school [1.45 (1.06, 1.97)] or attended college [1.36 (0.99, 1.88)] than those with less than high school education [1.02 (0.64, 1.61)].

3.3. Association between PA (Definition 2) and physical HRQoL

There was a significant relationship between poor physical health and no PA (p-value < 0.001) in Table 3. In Model 4, the OR (95% CI) for poor HRQoL was 1.80 (1.55, 2.01) for no PA and 1.27 (1.06, 1.52) for insufficiently active compared to active. The OR (95% CI) for poor HRQoL was 1.42 (1.19, 1.68) for no PA compared to insufficiently active (data not presented in the tables). We also found the association did not significantly differ by CHD groups, income, age or education [p_{for interaction} > 0.10] (Supplemental Table 2). However, the association differed by race (p-value = 0.010). It appeared stronger among non-Hispanic whites [2.11 (1.83, 2.44)] than in other races [1.23 (0.89, 1.69)].

Table 3:

Weighted analysis of the likelihood of having poor HRQoL^a among different levels of physical activity based on duration and frequency

	No. with poor HRQoL/ No. of participants	Model Ib OR (95% CI)	Model IIc OR (95% CI)	Model IIId OR (95% CI)	Model IVe OR (95% CI)
Physical Health
>150 min/wk	2195/9870	1 (ref)	1 (ref)	1 (ref)	1 (ref)
0-149 min/wk	1216/3713	1.64 (1.38, 1.94)	1.50 (1.26, 1.78)	1.35 (1.13, 1.61)	1.27 (1.06, 1.52)
No PA	3900/8353	2.85 (2.51, 3.24)	2.76 (2.43, 3.14)	1.97 (1.71, 2.27)	1.80 (1.55, 2.01)
p-value		< 0.001	< 0.001	< 0.001	< 0.001
Mental Health
>150 min/wk	1066/9870	1 (ref)	1 (ref)	1 (ref)	1 (ref)
0-149 min/wk	637/3713	1.45 (1.71, 1.79)	1.16 (0.93, 1.45)	1.03 (0.82, 1.29)	0.99 (0.79, 1.23)
No PA	1848/8353	1.95 (1.66, 2.29)	1.81 (1.53, 2.14)	1.24 (1.03, 1.50)	1.17 (0.97, 1.42)
p-value		< 0.001	< 0.001	0.037	0.12

Abbreviations: HRQoL – health related quality of life; No PA -no physical activity; wk – week; 0-149 min/wk -insufficiently active; >150 min/wk - active; OR -odds ratio; CI – confidence interval; ref – reference group

^aPoor HRQoL is defined as having 14 or more physical or mental unhealthy days

^bModel I: unadjusted model

^cModel II: adjusted for age, sex, race

^dModel III: adjusted for age, sex, race, education, income, smoking status, BMI, and number of chronic conditions

^eModel IV: adjusted for age, sex, race, education, income, smoking status, BMI, number of chronic conditions and CHD groups.

3.4. Association between PA (Definition 2) and mental HRQoL

We found a significant relationship between poor mental HRQoL and no PA (p-value < 0.001) in Models 1 to 3. In Model 4, the OR (95% CI) for poor HRQoL was 1.17 (0.97, 1.42) for no PA and 0.99 (0.79, 1.23) for insufficiently active compared to active individuals. We found the association did not differ by CHD groups, race or age [p_{for interaction} > 0.10] (Supplemental Table 2). However, it differed by income (p_{for interaction} = 0.04) and education (p_{for interaction} = 0.004). It appeared stronger in those with less than $25,000 [1.50 (1.15, 1.97)] than in those with more than $50,000 [1.21 (0.82, 1.80)] or than in those between $25,000 and $50,000 [0.79 (0.54, 1.16)]. Additionally, the association appeared stronger in those that graduated college [1.54 (1.10, 2.14)] or attended college [1.42 (1.06, 1.91)] or graduated high school [1.31 (95% CI 0.99, 1.73)] than in those with less than high school [0.86 (0.567, 1.29)]. Of note, the correlation between income and education was very low in this study (Pearson correlation coefficient r = 0.04, p-value < 0.01).

4.0. DISCUSSION

The primary purpose of this study was to investigate the association between physical inactivity and HRQoL in adults with CHD using the 2015 BRFSS. We found that physical inactivity assessed by two methods (level of intensity (Definition 1) and duration and frequency of PA (Definition 2) is associated with poor HRQoL in a multivariate analysis. Adults that reported no PA were more likely to have poor physical HRQoL than those who were engaged in vigorous PA (Definition 1) or were active (Definition 2). Also, physically inactive adults were more likely to have poor mental HRQoL than those engaged in vigorous physical activity. We found that the association between physical inactivity and HRQoL was stronger for physical HRQoL than mental HRQoL, and both associations did not differ by CHD groups or race. The association between physical inactivity and mental HRQoL appeared stronger in those with higher education. Our findings suggest that staying active is important in maintaining physical and mental HRQoL of CHD patients.

Our findings are consistent with studies that showed that PA is associated with overall health in cardiovascular patients.^34,47–49 In a large prospective cohort study of CHD patients undergoing cardiovascular rehabilitation, there was a 1% decrease in mortality with each additional exercise session attended.⁴⁹ Similarly, another cohort study of patients with stable CHD found that doubling the amount of physical activity from 0-5 MET hours/week to 5-10 MET hours/week reduced all-cause, cardiovascular and non-cardiovascular mortality by 10-20% after a median follow-up time of 3.7 years.⁵⁰ The largest reduction in mortality was seen among patients engaged in habitual exercise.

Our findings are also mostly in agreement with other studies.^51–53 In a cross-sectional study of individuals with chronic heart failure (CHF), physically inactive patients were four times more likely to have poor QoL versus those that were physically active.⁵³ Considering that the study found that even 6 minutes of walking per day was associated with improved quality of life, a small increase in PA among individual with CHF may produce marked benefits. However, a prospective study of adults with congenital heart disease found only a weak correlation between daily PA and QoL measured by SF36.⁵² One possible explanation for the weak correlation in that study is the high proportion of adults (76%) that met the recommended 150 min of at least moderate-intensity activity a week. This contrasts our study, where only 38% of adults met the recommended levels of PA.

Our findings enhance the current understanding of the association between physical inactivity and QoL of CHD survivors. There may be several reasons why physical inactivity has a negative impact on both physical and mental HRQoL. One such reason is the association between physical inactivity and individuals’ ability to perform normal daily activities. Research has shown that physical inactivity reduces the capacity for exercise and limits functional capacity.^51,54 Both reduced exercise and functional capacity are known to impair HRQoL.^51,54,55 Alternatively, in this cross-sectional study poor physical and/or mental HRQoL may lead to reduced physical activity.

Our study has several strengths. First, this large study is one of few studies that has examined the relationship between physical inactivity and the CDC HRQoL assessment in CHD patients, which has been validated using the SF36 HRQoL survey.^37,40–43 Second, the BRFSS uses an independent probability sample of households and trained interviews to obtain a representative sample of non-institutionalized U.S adults. Third, we had data on intensity and amount of physical activity and comprehensive information on covariates, which helped minimize sources of bias and confounding.

However, our study had several limitations. First, it was cross-sectional, which precluded the assessment of temporality and limited causal inference, particularly in this setting where the relationship between physical inactivity and HRQoL may be bidirectional. It is plausible that physical inactivity could lead to poor HRQoL, or physical and mental health may determine activity levels. The direction of this association will need to be determined by longitudinal or interventional studies. We also did not have information about the time of onset of CHD, duration of CHD, time since last event, or detailed information about severity. We were also unable to ascertain the amount of sedentary time or occupational physical demands. It is possible that different amounts of sedentary time or occupational physical activity may moderate our observed findings. Lastly, we only had self-reported PA, which could have created recall bias.

In conclusion, our findings suggest that among patients with CHD, physical inactivity is associated with poor physical and mental HRQoL after adjusting for various modifiable and non-modifiable risk factors. To the best of our knowledge, this is the first study that has looked at this association using the CDC HRQoL instrument. If confirmed by longitudinal studies, our findings would shed light on the importance of physical inactivity on the HRQoL of CHD patients. Together with other studies, our findings can inform the guidelines on physical activity and help shape policies/plans focused on increasing physical activity in this patient population.