1.1. Background
A significant social problem in Japan is the rapidly increasing number of older adults. In 2020, the number of people in the Japanese aged population (65 years old and over) was 36.19 million, constituting 28.8% of the total population [1]. A concern is an increase in medical costs associated with the aging of the population [2]. Increasing medical costs constitute a significant challenge for urban sustainability because the government's largest expenditures are related to social security expenditures, including medical costs [3]. A large proportion of medical costs are related to lifestyle-related diseases [4]. Lifestyle-related diseases are defined as a group of diseases whose onset and progression are related to lifestyle and behavior factors, such as dietary habits, physical activity, rest, smoking, and alcohol consumption [5]. For example, lifestyle-related diseases include diabetes, hypertension, heart diseases, and cerebrovascular diseases [5]. To prevent lifestyle-related diseases, the Japanese Ministry of Health, Labour and Welfare (MHLW) has developed the policy of “Healthy Japan 21” to promote the health of the people [6]. Prevention of lifestyle-related diseases is essential not only to reduce health care costs but also to extend people's healthy life expectancy [7]. Effective measures to prevent lifestyle-related diseases are diet/exercise, vitality/stress management, sleep, and cognition [8]. In particular, a very effective way is to incorporate walking into daily activities such as commuting to work [9].
This study's research question is as follows: Do changes in human mobility during the COVID-19 pandemic relate to the medical costs of lifestyle-related diseases? The pandemic forced people to reduce the frequency of outdoor activities and worsened their mental health [10]. It was also reported that the number of people using public transit declined markedly [11]. Japan had one of the most significant declines in human mobility worldwide [12]. With the pandemic continuing for two years, we need to investigate the “New-Normal” lifestyle. Studying human mobility in the context of the “New-Normal” lifestyle could provide valuable information for policy-makers and researchers in terms of prevention measures for not only infectious diseases but also lifestyle-related diseases.
1.2. Purpose
This study aims to clarify the correlation between the change in human mobility types and the medical costs of lifestyle-related diseases during the pandemic. Human mobility types are walking, driving, and public transit, according to the COVID-19 Apple Mobility Trends Reports [13]. The medical costs of lifestyle-related diseases were assessed for eleven diseases using the JAST Medical Dataset [14]. Based on a previous study [15], this study assessed eleven types of lifestyle-related diseases: diabetes mellitus, hypertensive diseases, disorders of lipoprotein metabolism and other lipidemia, disorders of purine and pyrimidine metabolism, fatty liver, atherosclerosis, intracerebral hemorrhage, cerebral infarction, angina pectoris, acute myocardial infarction, and subsequent myocardial infarction. The analysis method was boosted tree analysis.
The pandemic period in this study was set from January 2020 to September 2021. In Japan, the first case of SARS-CoV-2 infection was confirmed in January 2020 [16]. From April to May 2020, the first state of emergency was declared for all forty-seven prefectures [17]. In 2021, states of emergency were declared repeatedly, mainly in metropolitan prefectures, from January to February, April to June, and July to September. In September 2021, the emergency declaration was lifted for the last time because of the vaccination progress in Japan. In other words, the analysis period of this study, from January 2020 to September 2021, is the COVID-19 pandemic period in Japan.
This study analyzed all prefectures, divided into metropolitan and other prefectures. In Japan, prefectural governors have the authority to take measures to prevent the spread of infectious diseases based on special measures for pandemic influenza and new infectious disease preparedness and response [18]. In addition, prefectural governors have the authority to request that the central government declare a state of emergency [18]. Therefore, it is appropriate to analyze this study according to prefectures. The metropolitan prefectures are the Tokyo, Kanagawa, Chiba, Saitama, Osaka, Kyoto, and Hyogo prefectures in the Tokyo and Osaka metropolitan areas. The seven metropolitan prefectures declared states of emergency every time [17]. This study excludes the prefectures in the Nagoya metropolitan area because those prefectures did not declare states of emergency for some time. The other prefectures include forty prefectures in Japan.
1.3 Literature Review
Many studies have been conducted to reduce the medical costs related to lifestyle-related diseases from the viewpoint of human mobility. Regarding driving among the forms of human mobility, it was found that time and distance traveled by driving are statistically significantly positively associated with weight status, which is related to the obesity epidemic [19]. Therefore, instead of driving cars, using public transportation and walking reduced obesity-related medical costs [20]. For example, in Portland, it was found that opening the new public transit reduced the medical costs related to chronic diseases [21]. Among human mobility forms, walking has been analyzed for its effect in preventing lifestyle-related diseases [22, 23]. It was found that people who walk more than an hour a day experience a 15–20% increase in medical costs compared to those who walk less than 30 minutes a day [24]. In addition, the combinations of the risks of SM (ever smoking) and PI (walking for < 1 h/day), OB (BMI >/=25.0 kg/m) and PI, and SM and OB and PI were associated with a 31.4%, 16.4%, and 42.6% increase in medical costs, respectively [25]. Compared to previous studies, the novelty of this study is the analysis of the association between changes in human mobility and medical costs during the COVID-19 pandemic.
A characteristic feature of the COVID-19 pandemic is the restriction of human mobility to reduce the number of infections. During the pre-lockdown period in northern Italy, it was reported that 68% of people reduced their regular exercise [26]. In addition, in Australia, due to the COVID-19 pandemic, negative changes were noted for not only physical activity (48.9%) but also alcohol (26.6%) and smoking (6.9%) [27]. It was found that people endured and gradually adapted to these lifestyle changes [28]. It was found that a 554-step per-day decrease in mobility would increase functional status limitations by 5.9%, total medical expenditures by 0.9%, and nursing home utilization by 2.8% and decrease employment by 2.9%, earnings by 10.3%, and monetized QoL by 3.2% over 18 years [29]. In addition, it was found that people who tend toward restricting their daily activities to their bedroom had greater mean total medical costs than those who tend toward daily trips outside their town [30]. Some papers suggest that obesity and impaired metabolic health are both accelerators and consequences of severe infection [31]. Therefore, new evidence suggests the potential for health benefits by reducing sitting time and increasing moving time even during the pandemic [32]. Based on these studies, several states of emergency might seriously impact the medical costs related to lifestyle-related diseases. This study's novelty is the analysis of the correlation between human mobility and medical costs through the conduction of a retrospective study using statistical data.