**1. Introduction**

The increase in life expectancy of Japanese people is well-known worldwide [1]. Many studies have investigated the factors that determine the life expectancy of Japanese people [2]. In 2019, men had a life expectancy of 80.41, while healthy life expectancy was 72.68, a difference of 8.73 years. The average life expectancy of

women was 86.44 years, and the healthy life expectancy was 75.38 years, with a range of 12.06 years (Ministry of Health, Labor and Welfare 2022) [3].

In recent years, attention has been paid to the determinants regarding the average life expectancy and healthy life expectancy of older Japanese people. However, most of these studies used cross-sectional and ecological data [4, 5]. Therefore, it has been complicated and unclear to comprehensively analyze the causal structure, and various factors, including socioeconomic factors, for the healthy life expectancy of older people over their lifetime.

Canada's Lalonde Report [6] and USA Healthy People Strategy [7] addressed the importance of lifestyle habits related to diet and health, against the background that the contribution to medical health has not been significant to date. Many studies have explained the health effects of certain lifestyles [8, 9].

A favorable lifestyle reduces early mortality in people with specific diseases and lifestyles [10, 11]. In a large cohort of Japanese people, Tamakoshi et al. [12] showed that lifestyle significantly impacted life expectancy. However, lifestyle is not the only factor associated with individual survival days. Socioeconomic factors and the three health factors indicated by the WHO, physical and mental, and social factors, should also be considered.

Several reports highlight the impact of socioeconomic status on life expectancy. Socioeconomic differences were significantly associated with life expectancy [13, 14] and survival in older people [15]. Sugiura et al. [16] reported socioeconomic status as a background to the rapid increase in life expectancy of Japanese people after World War II. Considering the impact of Japan's socioeconomic position on health, Kagamori et al. [17] concluded that the difference in mortality was not trivial. However, research results have not been presented on the direct and indirect causal structure of socioeconomic conditions and life expectancy.

The World Health Organization (WHO) defines health as follows: Health is a better physical, mental, and social well-being, not merely the absence of illness or infirmity [18]. Based on this definition, studies have reported that three health-related aspects of physical, mental, and social well-being are related to life expectancy [19– 24], Specifically, physical activity and function [19, 20], cognitive vulnerability and self-rated health [21–23], and social connections [24] are statistically significantly related to survival in older adults. However, except for a few studies [25, 26], no studies have clarified causal structures associated with three health aspects, survival and socioeconomic status.

The fundamental hypothesis model is shown in **Figure 1**. This model indicates that healthy survival days and not-bedridden status would be determined by healthy dietary and lifestyle habits and three health-related dimensions based on socioeconomic status as a structural and causal relationship.

Therefore, the objectives of this chapter were to clarify the causal relationships among healthy dietary and lifestyle habits, socioeconomic status, and three healthrelated dimensions related to healthy longevity among Japanese elderly suburban dwellers. Covariance structure analysis clarified how large and causally each latent variable shown in **Figure 1** has a causal relationship with healthy longevity, a latent dependent variable.

It has become clear that it is essential to live satisfactorily in terms of health and the amount of annual income influenced by individual educational background.

What is the income threshold required to maintain survival? The relationship between per capita national product and average life expectancy for each country and its income threshold for longevity are reported. Here, a connection is shown in which

*Causal Structure for the Healthy Longevity Based on the Socioeconomic Status, Healthy… DOI: http://dx.doi.org/10.5772/intechopen.111910*

**Figure 1.**

*Causal structural relationships to the healthy longevity as a hypothesis model.*

the higher the per capita national product of a country, the longer the average life expectancy. When it exceeded more than 4.500 US \$, almost no extension of life expectancy was seen, and it occupied a practically constant level [27].

Costa Rica's average life expectancy, which is less than 10% of the per capita national product of the United States of America, was almost at the same level as that of the United States. In this way, along with the relationship between the value of national production and average life expectancy, the national product threshold has been clarified to ensure a certain average life expectancy [27].

However, no studies have been reported that clarify the annual income on an individual basis and the income threshold for maintaining a certain number of survival days, except in the six-year follow-up studies in urban suburbs and areas reported by the authors [25, 26].

Therefore, in this study, we will discuss the relationship between marital annual income and survival days in older people living at home in urban suburbs, citing a part of a previous study that also aimed to clarify the family yearly income threshold to ensure a certain number of survival days.

**Figure 2.**

*Relationship between marital annual income and survival days and the threshold as a hypothesis model.*

In the case of achieving the research purpose, the support method by health education specialists who support health is expected to be linked to new health support based on the process of taking into account the significance of the underlying income and enabling people to live positively against the background of a certain income, and as a result, specific desirable lifestyle habit might be maintained.

In addition to the significance of income, which is particularly important as a socioeconomic factor, it is expected that scientific income criteria regarding how much income can be used to maintain a certain level of survival can be presented.

We hypothesized that there is a significant relationship between annual marital income and survival days and that there is a threshold in this association. The hypothetical model is shown in **Figure 2**.

However, no studies have been reported that clarify the annual income on an individual basis and the income threshold for maintaining a certain number of survival days, except in the six-year follow-up studies in urban suburbs and areas reported by the authors [25].
