Television Viewing Time and 13-year Mortality in Adults with Cardiovascular Disease: Data from the Australian Diabetes, Obesity and Lifestyle Study (AusDiab)

Background

In the general population, excessive sedentary behaviour is associated with increased all-cause mortality. Few studies have examined this relationship in people with cardiovascular disease (CVD). Using a sample of people with CVD who were excluded from an analysis of the Australian Diabetes, Obesity and Lifestyle (AusDiab) study, we examined the relationship between sedentary behaviour and 13-year all-cause mortality.

Methods

In the original AusDiab study, television viewing time was used as a marker of sedentary behaviour in 609 adults (≥45 years of age) with CVD. During 6,291 person-years of follow-up (median follow-up 13 years), there were 294 deaths (48% of sample). Using the time scale of attained age, the Cox proportional hazards model predicting all-cause mortality adjusted for sex, self-rated general health, leisure-time physical activity, smoking status, education, household income, body mass index, lipid levels, blood pressure, and diabetes mellitus was used.

Results

Compared with a TV viewing time of <2 hours per day, the fully adjusted hazard ratios for all-cause mortality were 1.18 (95% CI, 0.88 to 1.57) for ≥2 to <4 hours per day and 1.52 (95% CI, 1.09 to 2.13) for >4 hours per day.

Conclusions

Sedentary behaviour was associated with increased risk of all-cause mortality in people with CVD, independent of physical activity and other confounders. In addition to the promotion of regular physical activity, cardiac rehabilitation efforts which also focus on reducing sedentary behaviour may be beneficial.

Introduction

Adults in the general population spend more than half of their waking hours engaged in sedentary behaviours [1]. Sedentary behaviour refers to any waking behaviour characterised by low energy expenditure while in a sitting or reclining posture [2] and is a distinct behavioural entity from insufficient physical activity (PA) [3]. While more sophisticated measures of sedentary behaviour are now available [4], early studies in this area typically used television (TV) viewing as a marker of sedentary behaviour [5], [6]. Television viewing occupies a large amount of adults’ leisure time [7] and is particularly prevalent in older adults, who typically watch between three and five hours of TV per day [8]. High TV viewing is associated with low household income, low education, poor self-rated health [9], and the consumption of energy-dense snack foods [10].

Cardiovascular disease (CVD), including coronary heart disease (CHD) and stroke, is the leading cause of death and disability worldwide [11]. People who survive an acute event are at an increased risk of a subsequent event and premature death [12]. Physical activity is a unique form of treatment and management for CVD because it contributes to lowering physiological risk factors [13], [14], reducing premature all-cause and cardiac-related mortality [15] and morbidity [16], and improving quality of life and psychological wellbeing [17]. Adults with CVD are less likely to engage in sufficient PA than the general population [18], [19]. Emerging evidence suggests that people with CVD engage in more sedentary behaviour than those without CVD [18], [19]. To our knowledge, no studies have investigated the prevalence of sedentary behaviour in Australians with CVD.

Over the past decade, research in the general adult population has consistently shown an association between TV viewing time and poor health outcomes, independent of PA levels. Excessive TV viewing is associated with increased risk of all-cause [5], [20], [21], [22] and CVD [5], [21], [22] mortality as well as higher morbidity, including higher rates of CVD [5], [20], [22], [23], [24], type 2 diabetes [25] and depression [26], independent of confounding factors such as age [27], [28], lower education levels [29], [30], [31], [32], smoking [31], higher waist circumference/body mass index (BMI) [31], serum triglycerides [5], blood pressure [5], total cholesterol [5], high-density-lipoprotein cholesterol (HDL-C) [5] and PA [31]. Even adults who meet the minimum PA recommendations remain at risk of poorer health if they spend excessive amounts of time engaged in TV viewing [22], [27], [33].

To ensure results are not biased by the presence of illness categories, the majority of population-based studies of sedentary behaviour and health have excluded people with established CVD [5], [20], [21], [22]. In a large population study of Australian adults, Van der Ploeg and colleagues [34] found consistent associations, independent of PA levels, between self-reported sitting time and all-cause mortality among healthy participants and also among those with pre-existing CVD, diabetes mellitus and overweight/obesity. While these findings highlight the importance of investigating not only healthy but also chronically ill populations, the impact of sedentary behaviour on mortality risk in adults with existing CVD is unknown.

The present study replicates the approach used in the Australian Diabetes, Obesity and Lifestyle (AusDiab) study with the sub-sample of patients with self-reported CVD who were excluded from the original study [5]. The primary aim was to investigate the association between TV viewing time and 13-year all-cause mortality. Television viewing was used in the original AusDiab study as the indicator of sedentary behaviour. The secondary aims were to examine the amount of time spent in TV viewing among people with CVD and to characterise high versus low TV viewers according to sociodemographic and lifestyle factors, medical conditions and cardiometabolic health outcomes.