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.

Little is known about the trade-off between the health benefits of physical activity (PA) and the potential harmful effects of increased exposure to air pollution during outdoor PA. We examined the association of the combined effects of air pollution and changes in PA with cardiovascular disease (CVD) in young adults. This nationwide cohort study included 1 469 972 young adults aged 20–39 years. Air pollution exposure was estimated by the annual average cumulative level of particulate matter (PM). PA was calculated as minutes of metabolic equivalent tasks per week (MET-min/week) based on two consecutive health examinations from 2009 to 2012. Compared with the participants exposed to low-to-moderate levels of PM2.5 or PM10 who continuously engaged in ≥1000 MET-min/week of PA, those who decreased their PA from ≥1000 MET-min/week to 1–499 MET-min/week [PM10 adjusted hazard ratio (aHR) 1.22; 95% confidence interval (CI) 1.00–1.48] and to 0 MET-min/week (physically inactive; PM10 aHR 1.38; 95% CI 1.07–1.78) had an increased risk of CVD (P for trend <0.01). Among participants exposed to high levels of PM2.5 or PM10, the risk of CVD was elevated with an increase in PA above 1000 MET-min/week. Reducing PA may lead to subsequent elevation of CVD risk in young adults exposed to low-to-moderate levels of PM2.5 or PM10, whereas a large increase in PA in a high-pollution environment may adversely affect cardiovascular health. Combined effects of air pollution and changes in physical activity with cardiovascular disease in young adults.

The health benefits of physical activity have been well established. However, more than a quarter of the adult population in the world is insufficiently active (not performing at least 150 minutes of moderate-intensity physical activity per week, 75 minutes of vigorous-intensity physical activity per week, or any equivalent combination of the two), and there has been little improvement since 2001. In South Korea, the prevalence of insufficient physical activity was 54.4% in adults and 94.1% in adolescents in 2020. There was continuous decrease in the prevalence of sufficient aerobic physical activity, from 58.3% in 2014 to 45.6% in 2020. However, daily duration of sedentary behavior increased from 7.5 to 8.6 hours in the same period. Interventions to promote physical activity are necessary in various fields including clinical and policy approaches. As physical activity has decreased during the coronavirus disease 2019 pandemic, safer and more effective strategies to promote physical activity are required.

In a cohort of 190,599 participants from The National Health Insurance Service-National Health Screening (NHIS-HEALS) study, we investigated the association of changes in the predicted body composition and metabolic profiles with the risk of metabolic syndrome (MetS) in the general population, which was hitherto incompletely elucidated. At baseline and follow-up examinations, the body composition, including lean body mass (LBM), body fat mass (BFM), and appendicular skeletal mass (ASM), were estimated using a prediction equation, and the risk of MetS was analyzed according to relative body composition changes. An increase in relative LBM and ASM decreased the risk of MetS in men and women (adjusted odds ratio (aOR), 0.78 and 0.80; 95% confidence interval (CI), 0.77–0.79 and 0.79–0.81, respectively; all p < 0.001). As relative LBM and ASM increased, the risk of MetS was more significantly reduced in the group with higher baseline BMI and body fat mass index (BFMI)(all p-trend < 0.001). In men, when the relative LBM increased (aOR, 0.68; 95% CI, 0.63–0.73), the risk of MetS was low despite increased BMI. Thus, our findings suggested that an increase in the relative LBM and ASM reduced the risk of MetS, whereas an increase in the relative BFMI increased the risk of MetS; this result was consistent in men despite an increase in BMI.

Seogsong Jeong, Yun Hwan Oh, Seulggie Choi, Jooyoung Chang, Sung Min Kim, Joung Sik Son, Gyeongsil Lee, Won Kim, and Sang Min Park. Gut and Liver 2022;16:589-98. https://doi.org/10.5009/gnl210256

Seogsong Jeong, Yun Hwan Oh, Seulggie Choi, Jooyoung Chang, Sung Min Kim, Sun Jae Park, Yoosun Cho, Joung Sik Son, Gyeongsil Lee, and Sang Min Park. Gut and Liver -0001;0:. https://doi.org/10.5009/gnl220038