1Department of Family Medicine, Jeju National University Hospital, Jeju, Korea

1Department of Family Medicine, Jeju National University Hospital, Jeju, Korea

2Department of Family Medicine, Jeju National University School of Medicine, Jeju, Korea

1Department of Family Medicine, Jeju National University Hospital, Jeju, Korea

2Department of Family Medicine, Jeju National University School of Medicine, Jeju, Korea

1Department of Family Medicine, Jeju National University Hospital, Jeju, Korea

2Department of Family Medicine, Jeju National University School of Medicine, Jeju, Korea

1Department of Family Medicine, Jeju National University Hospital, Jeju, Korea

2Department of Family Medicine, Jeju National University School of Medicine, Jeju, Korea

One-third of the global population aged 15 years and older engages in insufficient physical activities, which affects health. However, the health risks posed by sedentary behaviors are not well known. The mean daily duration of sedentary behavior is 8.3 hours among the Korean population and 7.7 hours among the American adult population. Sedentary lifestyles are spreading worldwide because of a lack of available spaces for exercise, increased occupational sedentary behaviors such as office work, and the increased penetration of television and video devices. Consequently, the associated health problems are on the rise. A sedentary lifestyle affects the human body through various mechanisms. Sedentary behaviors reduce lipoprotein lipase activity, muscle glucose, protein transporter activities, impair lipid metabolism, and diminish carbohydrate metabolism. Furthermore, it decreases cardiac output and systemic blood flow while activating the sympathetic nervous system, ultimately reducing insulin sensitivity and vascular function. It also alters the insulin-like growth factor axis and the circulation levels of sex hormones, which elevates the incidence of hormone-related cancers. Increased sedentary time impairs the gravitostat, the body’s weight homeostat, and weight gain, adiposity, and elevated chronic inflammation caused by sedentary behavior are risk factors for cancer. Sedentary behaviors have wide-ranging adverse impacts on the human body including increased all-cause mortality, cardiovascular disease mortality, cancer risk, and risks of metabolic disorders such as diabetes mellitus, hypertension, and dyslipidemia; musculoskeletal disorders such as arthralgia and osteoporosis; depression; and, cognitive impairment. Therefore, reducing sedentary behaviors and increasing physical activity are both important to promote public health.

Approximately 31% of the global population aged ≥15 years engages in insufficient physical activity, and it is known to contribute to the death of approximately 3.2 million people every year [1]. In South Korea, the physical activity rate is on the decline among adults aged ≥19 years, irrespective of the type of activity, including aerobic exercise, walking, and muscle training. Therefore, in 2017, the rates of aerobic exercise, walking, and muscle training in the Korean adult population were 48.5%, 39.0%, and 21.6%, respectively, with the majority of the Korean population engaging in physical inactivity [2]. In addition to physical inactivity, sedentary behavior is also a serious problem, and a substantial number of people engage in it for prolonged periods. For instance, Americans spend 55% of their waking time (7.7 hours a day) engaged in sedentary behaviors whereas Europeans spend 40% of their leisure time (2.7 hours a day) watching television [3]. Similar patterns have been observed in Koreans, who have been reported to demonstrate long sedentary times. According to Korea Health Statistics of 2018, adults in Korea aged ≥19 years engage in 8.3 hours of sedentary time. Only 8.9% of the adult population engaged in 12 hours of sedentary time [4].

A poor participation in physical activity is speculated to be influenced by multiple factors. Some environmental factors include traffic congestion, air pollution, shortage of parks or pedestrian walkways, and a lack of sports or leisure facilities [1]. Television viewing, video viewing, and cell phone usage are positively correlated with an increasingly sedentary lifestyle [5]. Sedentary behaviors are projected to continue to rise on the basis of this socio-cultural background.

Sedentary lifestyles have a major impact on the overall health of the global population. Many people worldwide engage in sedentary lifestyles, and the prevalence of relevant non-communicable diseases is on the rise. It is well known that insufficient physical activity, that is, physical inactivity, has a detrimental effect on health. Physical inactivity is the fourth leading risk factor for global mortality, accounting for 6% of global mortality [6]. Despite the fact that sedentary behavior poses a comparable risk to health and contributes to the prevalence of various diseases, most physical activity-related education in clinical practice is focused on improving the physical activity levels, with less emphasis on lowering the sedentary behavior. In addition to understanding and informing patients about the health impact of a sedentary lifestyle, healthcare providers of various fields, including clinicians, should reflect upon its significance in policies. This study examined the effects of a sedentary lifestyle on health and the lifestyle-related improvements to be made to promote healthy living.

Sedentary behavior is defined as any waking behavior such as sitting or leaning with an energy expenditure of 1.5 metabolic equivalent task (MET) or less [7]. This definition, proposed by the Sedentary Behavior Research Network in 2012, is currently the most widely used definition of sedentary behavior. Some examples of sedentary behavior include television viewing, playing video games, using a computer, sitting at school or work, and sitting while commuting (Figure 1) [8]. According to the 2011 Compendium of Physical Activities, MET is defined as the ratio of work metabolic rate to the standard resting metabolic rate (RMR) of 1 kcal/(kg/h). One MET is the RMR or energy cost for a person at rest. When classified quantitatively based on their intensities, physical activities can be classified into 1.0–1.5 METs (sedentary behavior), 1.6–2.9 METs (light intensity), 3–5.9 (moderate intensity), and ≥6 METs (vigorous intensity) (Figure 2) [9].

Examples of sedentary behavior. (A) Playing a video game. (B) Watching television. (C) Using a computer. (D) Reading a book.

Examples of moderate to vigorous physical activity. (A) Riding a bicycle. (B) Running.

A sedentary lifestyle increases all-cause mortality and the risks for cardiovascular diseases (CVD), diabetes mellitus (DM), hypertension (HTN), and cancers (breast, colon, colorectal, endometrial, and epithelial ovarian cancer). This has been consistently documented in the literature [3,10,11]. There is no disagreement on the fact that prolonged total sedentary behavior times are associated with poor disease outcomes. However, the patterns of sedentary time may differ even within the same total amount of time, and not much is known about the particular patterns of prolonged sedentary time that pose more significant health hazards (for example, continuous sedentary behavior without a break or intermittent sedentary behavior) [12]. One study reported that even if the total sedentary time was equal, having short sedentary bouts and engaging in physical activities intermittently can have relative health benefits. The total sedentary time and moderate-to-vigorous physical activity (MVPA) have been reported to be negatively correlated, where the waist circumference (standardized β, -0.16; 95% confidence interval [CI], -0.31 to -0.02; P=0.026), body mass index (β, -0.19; 95% CI, -0.35 to -0.02; P=0.026), triglyceride level (β, -0.18; 95% CI, -0.34 to -0.02; P=0.029), and 2-hour postprandial plasma glucose level (β, -0.18; 95% CI, -0.34 to -0.02; P=0.025) decreased with increasing the number of breaks in the sedentary time [13]. Furthermore, when the sedentary time was interrupted with light- or moderate-intensity physical activity, the systolic and diastolic blood pressures dropped by 2–3 mm Hg whereas interrupting the sedentary time with light-intensity physical activity (LIPA) or simple muscle training in patients with diabetes (88% of the population had HTN) decreased the systolic pressure by 14–16 mm Hg and the diastolic pressure by 8–10 mm Hg [14].

The exact mechanisms of the various adverse effects of sedentary behavior on the human body are currently unknown. However, several hypotheses have been proposed for the overall understanding of the impact of sedentary behavior on the human body, which are described below.

Sedentary lifestyles are associated with metabolic dysfunctions, such as elevated plasma triglycerides and high-density lipoprotein (HDL) cholesterol and reduced insulin sensitivity [15,16]. Lipoprotein lipase (LPL) is a protein that interacts at the cellular level, and a low LPL concentration is known to decrease the plasma HDL cholesterol level, while affecting the prevalence of severe HTN, diabetes-induced dyslipidemia, metabolic disorders caused by aging, metabolic syndrome, and coronary artery diseases. Moreover, LPL activity is diminished by physical inactivity. Additionally, physical inactivity inhibits LPL activity in skeletal muscles and rapidly signals for impaired lipid metabolism. In an experiment based on a rat model, the reduction of LPL activity in rats that engaged in light walking was only about 10% of the LPL activity in rats that were only placed in their cages [17]. The fact that muscle LPL activity is highly sensitive to physical inactivity and low-intensity muscular contractile activity can serve as evidence supporting the theory that sedentary behavior is a risk factor for various metabolic disorders [18].

Physical inactivity reduces bone mineral density [19]. In a study on healthy adult men and women, 12 weeks of bed rest decreased the mineral density of the lumbar spine, femoral neck, and greater trochanter by 1%–4% [19]. The balance between bone resorption and bone deposition mediates the relationship between sedentary behavior and the reduction of bone mineral density. According to some studies, bed rest elevates bone resorption markers and does not influence bone formation markers [20-22].

Some studies have provided limited evidence that sedentary behavior has a negative impact on vascular health. A study on healthy women reported that 56 days of head-down bed rest decreased the endothelium-dependent vasodilation while increasing the endothelial cell damage. Such alterations in vascular function were prevented through aerobic exercise and muscle training [23].

A sedentary lifestyle is strongly associated with CVD, DM, cancer, and premature mortality. The total daily sedentary time and television viewing time were correlated with an increased all-cause mortality risk [24]. In a study analyzing the mortality rates of people with >10 hours and