The objective of this study was to assess the association of two common sedentary behaviors, riding in a car and watching TV, with CVD mortality in men. In age-adjusted analysis, TV watching, riding in a car and combined sedentary behavior were significantly associated with risk of CVD mortality. However, multivariate-adjusted analysis resulted in no association of time watching TV and CVD mortality risk. Riding in a car (>10 hrs/wk) and combined sedentary behavior (>23 hrs/wk) remained significantly associated with 48% and 37% increased risk of CVD mortality, respectively, as compared with the referent groups (<4 hrs/wk and <11 hrs/wk). Results further showed, regardless of time spent in riding in a car or in combined sedentary behavior, being older, normal weight, normotensive, and physically active were associated with a lower risk of CVD mortality in this cohort.
Beginning in the 1950s, physical inactivity was reported to be associated with atherosclerosis (32
). Since that time, evidence has accumulated linking physical inactivity to incident CVD (1
). Emerging physical inactivity research assesses the role of various sedentary behaviors. During the last decade, numerous epidemiological studies have shown indicators of physical inactivity, such as TV viewing, driving in a car and sitting, are strongly related to the risk for developing dyslipidemia (1
), obesity (24
), type 2 diabetes (21
), hypertension (3
), metabolic syndrome (18
), and CVD (2
). Limited studies have also revealed that sedentary behavior may increase the risk for CVD mortality (24
). Despite these findings, to date there are no public health recommendations for adults regarding the amount of time an individual should spend engaged in sedentary behaviors (19
Very few studies have assessed the independent association of time spent riding in a vehicle and CVD mortality. Some of the early work on this topic by Morris and colleagues (32
) showed a positive relationship between men with sedentary occupations and the incidence of CVD mortality. In that study, London bus drivers were 1.8 times more likely than bus conductors to develop coronary heart disease (32
). Actual time spent driving a bus was not assessed; however, it can be assumed that bus drivers spent more weekly hours driving compared to bus conductors. The present study indicated that riding in a car >10 hours/week increased CVD mortality risk by 48%. Further research in diverse groups of men and women are needed to clarify the relationship between hours spent riding in a car and risk of CVD mortality.
Research suggests that, on average, adults are quite sedentary spending ≥7.7 hours/day involved in activities resulting in very low energy expenditure (8
). Recent reports estimate that more than 60% of American adults are not regularly active, and 25% of the adult population is physically inactive (9
). More recently, it was reported that a large percentage of daily energy expenditure comes from sedentary behaviors and leisure time activities. Dong et al. (14
) reported driving a car and TV watching as the second and fourth largest contributors to daily energy expenditure, respectively. Despite no other studies relating total sedentary behavior to CVD risk factors, incidence, or mortality having been published, our results, combined with previous findings, indicate that decreasing time spent in total sedentary behavior may increase overall physical activity and energy expenditure and, therefore, decrease the risk of CVD mortality.
Another major finding of our study was that, for any given amount of time spent riding in a car, men who were physically active () maintained lower CVD mortality rates than men who were classified as physically inactive. Research indicates that physical activity is protective against CVD mortality (16
), and that less-active individuals have a greater associated risk of obesity (7
), hypertension (3
), diabetes (18
), and some forms of cancer (20
), thus resulting in increased mortality (15
). Previous ACLS reports have shown that being aerobically unfit due to insufficient amounts of regular physical activity is an independent predictor of mortality and nonfatal disease (34
). In addition, other evidence indicates that higher levels of aerobic fitness, a strong indicator of a person’s recent level of physical activity, is protective against all-cause and CVD mortality in men in the presence of overweight and obesity (37
), type 2 diabetes (10
), and hypertension (12
). One other study of sedentary behavior determined that physically active men and women had lower rates of CVD mortality in the presence of elevated time spent sitting (27
). The current study’s findings add to the cumulative evidence for the benefits of being physically active despite the presence of other potentially health-diminishing behaviors and conditions.
A growing body of research is beginning to elucidate the mechanistic pathways that contribute to the health risks associated with sedentary behaviors. Some of the mechanisms may include adverse alterations to cardiac function, glucose homeostasis, and lipid metabolism (4
). Recent findings suggest that physiologic mechanisms associated with excessive sedentary behavior are different than the physiologic benefits of regular exercise (18
). This may help to partially explain the elevated risk of CVD mortality noted in physically active men who also demonstrated high levels of total sedentary behavior in the current study. Additional research to ascertain the pathophysiologic mechanisms associated with total and segmented components of sedentary behavior is well warranted.
This study had several strengths. The relatively long follow-up (21 years) was sufficient to accumulate enough fatal end-points to assess the association of sedentary behaviors and CVD mortality. An extensive physical examination also provided detailed information on the absence or presence of medical conditions and CVD risk factors. The limitations of the study include the representativeness of the study cohort, which was male, primarily white, well-educated, and in middle to upper socioeconomic status. Thus, results may not be generalized to other populations; however, it should not affect the internal validity, which may be considered a strength. There may be confounding subclinical diseases affecting the outcome of the study. However, the probability of these diseases affecting the relationship between sedentary behavior and CVD mortality is low, especially when considering the extensive baseline medical examination and observing a lack of change in the associations when eliminating participants with CVD events in year one of follow-up. Data were only available at baseline, so changes in the exposure variables during the follow-up period could not be assessed. Although true exposure could have changed significantly within many subjects during follow-up, there was still a remarkably strong relationship between time spent riding in a car and CVD mortality. This source of error likely led to an underestimation of the full magnitude of sedentary behavior upon the risk of CVD mortality. The status of being physically inactive or active was self-reported with a very crude assessment and could have resulted in some misclassification. Finally, we do not have sufficient data on diet and medication usage to include in the analytic models. Despite these limitations, the results revealed a strong association between self-reported sedentary behaviors and CVD mortality risk.
The magnitude of the association between combined sedentary behavior and CVD mortality observed in this study is clinically relevant. In this prospective study of 7,744 men, participants were at significantly greater risk of CVD mortality if they reported riding in a car >10 hours/week or participated in >23 hours/week of combined sedentary behaviors. Therefore, we suggest that men, in combination with increasing their level of physical activity, also reduce sedentary behavior to diminish their risk of CVD mortality. This study provides further evidence that formal recommendations on limiting sedentary behavior in persons of varying age should be developed to provide public health professionals and clinical practitioners with information to improve their effectiveness in promoting physical activity and health (19