Education as a Moderator in the Effect of Successful Aging on Mortality Risk in Elderly Chinese: A National Longitudinal Study (2011-2016)

Abstract

Background

Some studies have found that successful aging and its components were significantly associated with older adults’ health, their achievement has a positive effect on reducing mortality rates. However, there is little evidence to discuss whether education could modify the effect of successful aging on morality risk. Numerous literatures from worldwide were cross-sectional and previous studies on the association between successful aging and mortality in China were quite few. We aim to evaluate the effect of successful aging and each of its components on mortality risk of older in China, further discussed whether education was a moderator in this effect and investigated differences in results among males and females.

Methods

Data was derived from CHARLS (China Health and Retirement Longitudinal Study), which is a nationally representative follow-up survey. Cox proportional hazards models were used to estimate the education's moderate effect on the relationship between successful aging and mortality.

Results

In total, 4824 residents aged 60 years and above were recorded. 15.18% (n=367) for males and 15.74% (n=379) for females were defined as successful aging and the mortality were 2.61% (n=63) for males and 3.45% (n=83) for females during the survey. It is the first longitudinal study using national cohort data to research the educational effects on the association between mortality and successful aging, our study showed that the effect only existed in females aged 65-74 years old group with lower education.

Conclusions

Education has the significant effect on the relationship between successful aging and mortality. Physical health is significantly associated with the achieving of successful aging among young older. More measures should be paid on improving mental health among the young female older with lower education to achieve successful aging and to against mortality and live longevity. 

Introduction

Faced with life expectancy increased dramatically, the world’s demographic structure has changed significantly[1]. It is predicted that almost 2 billion people will be 60 years or older by the year 2050, accounting for 20% of the global population, aging populations pose economic challenges to society[2].Social attention about aging has shifted from “how to live longer” to “how to age well”, how can people age well? Many people, all around the world, regard good health as an important goal in their lives[3].

The concept of successful aging which was closely connected with good health has evolved for several decades, there is no agreed-upon definition of successful aging. This term was introduced by Robert J. Havighurst who first proposed the concept of successful aging[4, 5]. Rowe and Kahn discussed the operational concept of successful aging that encompasses three main criteria: low risk of disease and disability, maintenance of high physical and cognitive functioning, as well as active engagement in social and productive activities[6]. In recent years, the World Health Organization (WHO) reported the concept of active aging, which is “the process of optimizing opportunities for health, participation and security in order to enhance the quality life as people age”[7]. Several empirical studies nowadays have recognized the successful aging as a “calculable gold standard of aging”[8].

Although there are different defined successful aging across countries, cultures and literature, a majority of researches of successful aging has already paid attention to the factors which is associated with the achievement of successful aging and the prediction of future health outcomes result from successful aging[9, 10].A considerable number of studies have found that individual components (absence of major disease, freedom from disability, high cognitive function, no depressive symptoms, active social engagement in life) of successful aging were significantly associated with older adults’ health[11–14], their achievement has a positive effect on reducing mortality rates.

Education, as the common proxy for socioeconomic status (SES), makes it possible for individuals to master more knowledge about diseases, to understand the health treatments and cope with mechanisms for ill-health[15]. In empirical studies, numerous of them have provided evidence that education significantly contributed to the prediction of reaching successful aging[9, 16, 17]. Studies of 20th century found that higher educational level were linked with robust aging[9, 16–20]. Recent studies of Chinese elderly in Hong Kong and Shanghai have identified education as determinants of successful aging, higher educational level was related to higher rate of successful aging and the rate of successful aging was differ from years of education[21, 22]. Education is also associated with psychological and biological conditions, two main criteria of successful aging, among the elderly, which means low levels of education were linked with poorer psychological function (depressive symptoms) and poorer biological conditions (diseases and disability)[23].

Higher socioeconomic status(age/gender/education), longer life expectancy and lower morbidity is positively associated with successful aging[24], indicating that better education is likely to prevent populations from high mortality risk, meaning the mortality rate might be higher who did not achieve successful aging than in their counterparts.. Hence, it is of great interest to explore relationship between successful aging and mortality. However, there is little evidence to discuss health outcomes derived from successful aging and whether education can modify the effect of successful aging on morality risk. Furthermore, studies from worldwide were most cross-sectional and association between successful aging and mortality among Chinese elderly has remained unexplored thus far.

On the basis of above literature review, we hypothesized that successful aging would be associated with education and different levels of education, and education may modify the effect of successful aging on morality risk. Another primary hypothesis was that the effect as mentioned above experience gender difference, which means gender disparities may exist in the health indicators of mortality among successful aging population and non-successful aging population. So this prospective study first aims to evaluate the effect of successful aging and each of its components on mortality risk of the elderly aged 60 and over in China, the analyses of study population were classified into two group (60–74 years/75 years or older) because the effect may be different between young-old and old-old; we further discussed whether education plays a moderator role in this effect using nationally representative longitudinal data..

Methods

Definition Of Successful Aging

Our concept of successful aging took the definition of Rowe and Kahn[6], including the following 5 components: 1) absence of major diseases, 2) freedom from disability, 3) high cognitive function, 4) no depressive symptoms, 5) active social engagement in life.

1 Absence of major diseases: To judge the status of chronic diseases, respondents were asked by the following question: “Have you been diagnosed with conditions listed below by a doctor?” The conditions include cancer, chronic lung disease, diabetes, heart disease and stroke. The research indicated that those diseases mentioned above may cause major disease burden for the elder[26], the respondents were classified as having no major diseases if they reported have no any of the above five chronic diseases.

2 Freedom from disability: The activities of daily living (ADL) scale was used to assess the ADLs[27], according to the following questions: “Because of a physical, mental, emotional or memory problem, do you have any difficulty with one type of everyday activity, excluding any that you expect to last less than three months?” The everyday activities include dressing, bathing, or showering, eating, getting into or out of bed, using the toilet, and controlling urination and defecation. Respondents were classified as having no disability if they reported that they had no difficulty with the everyday activities of six items mentioned above.

3 High cognitive function[14] : Cognitive function was assessed with the Telephone Interview of Cognitive Status (TICS).This includes both immediate and delayed recall of ten words on a list, serial subtraction of seven from 100 (up to five times), and naming the day of the week, month, day, year, and season, and drawing the picture. The score of cognitive function ranged from 0 to 21. Respondents were considered to have high cognitive functioning if they achieved a median or above score, and the median score was 11.

4 No depressive symptoms: Depressive symptoms were assessed using the CES-D 10 (10-item Center for Epidemiological Studies Depression Scale). The cut-off value is less than 10 points, which was used to identify no depressive symptoms.

5 Active social engagement in life: Respondents were defined as being actively social engaged if they participate in any of the following types of social groups: voluntary or charity work, provided help to family, friends, or neighbors, gone to a sport, social, or other kind of club in the month preceding the interview. The participant who met all five indicator criteria mentioned above was defined as “successful aging”, otherwise as “non-successful aging”.

Other Variables

Control variables includes following factors: age (60–74 years/75 years or older), gender (Male/Female), education level (Primary school and below/Junior high school or above), income ( low: <650yuan,medium: 650-100580yuan,high:>10058yuan) marital status (Married/Cohabitating/Divorced/Separated/Widowed/Never married), community type (Rural/Urban), smoking (Yes/No/Quit), and drinking (Drink more than once a month/Drink but less than once a month/Do not drink).

Mortality

Participants enrolled in W1 were followed up in W2, W3 and W4. We collected the all-cause mortality and survival information of the respondents during the four wave surveys (2011–2015). W2 recorded of the respondents’ both status information (dead or alive) and death time, while W3 and W4 only provided the interview status information (dead or alive). We recorded and calculated the survival time of those who had the accurate all-cause death time by the interval between the interview time of W1 and the death time in W2. If respondents’ accurate death time was not available, we calculated the specific value by the interval between the interview time of W1 and the specific wave with death information and then defined the median of this value as the survival time. The survival time of those who were alive during whole follow-up interview was the interval between W1 and W4.

Statistics Analysis

All descriptive statistical analyses were performed by gender. We first used chi-square test to compare individual characteristics (including dichotomous or categorical variables) with and without successful aging. Next, the survival analysis was used to examine the association between successful aging and all-cause mortality, the Cox proportional hazards regression models were used to estimate the unadjusted and adjusted hazard rations (HRs) and 95% confidence intervals (CLs) of successful aging. At last, whether the education could modify the effect of successful aging on the all-cause mortality was assessed, in this stage, we also used the Cox proportional hazards regression models to examine the educational mediating effect on all-cause mortality among successful aging and non-successful aging populations. All statistical analyses were performed by SAS 9.3. The significance level was set at 0.05.

Results

Table 1 shows the respondents’ baseline characteristics according to successful aging. In the group aged 60–74 years old, 15.20% (n = 297) for males and 15.95% (n = 305) for females were defined as successful aging according to our definition. Among males and females, people with high education level were likely to achieve successful aging compared with lower education (P < 0.001). Higher income makes it possible for people to achieve successful aging (P < 0.01). People keeping the drinking habits (Drink but less than once a month and Drink more than once a month, P < 0.001) were more likely to achieve aging successfully, compared with the people (Do not drink). In addition, smokers were more likely to be successfully aging in male group (P = 0.001). For the group of 75 years old and above, the successful aging rate was 15.12% (n = 70) for males and 14.95% (n = 74) for females respectively. The connection between successful aging and education was similar among the group aged 60–74 years old. Other details of characteristics of participants were shown in Table 1.

[Insert Table 1 here]

As Table 2 shows, among population aged 60–74, the mortality rate of females (3.50%) was higher than males (2.46%), although the difference was not significant (P = 0.055). Moreover, the distribution of the association between successful aging and its components and mortality differed by gender, the association between successful aging and mortality was significant in females (P = 0.033), but not in males (P = 0.200). Specifically speaking, individual components comprising successful aging except "Active social engagement in life (P = 0.642)" in females were associated with mortality significantly, and those significant correlation in males only existed in " Absence of major disease (P๤0.001)" and" Freedom from disability (P๤0.001)". Among group aged 75 and above, the mortality rate of males and females were similar (males = 3.24%, female = 3.23%, P = 0.995). In addition, both males and females showed the same correlation trend between successful aging and its components and mortality except " Absence of major disease (P = 0.004)" was associated with mortality in males and "High cognitive function (P = 0.021)" was associated with mortality in females.

[Insert Table 2 here]

In order to assess the risk of mortality onset, the Cox proportional hazards models were used to show relevant results during the follow-up survey according to the successful aging at baseline participants (Table 3).In total, after adjusting education, health behavioral and relevant influencing factors, the association between successful aging and mortality was only observed in the group aged 60–74 in females (HR = 3.105, 95%CI = 1.128–8.543). However, there was no association between successful aging and mortality significantly in males. In addition, owing to the restriction of data, the females aged 75 and above cannot observe similar correlation (females defined as aging successfully had no death data at that age stage).

[Insert Table 3 here]

The study further explored if the education was a moderator in this effect of successful aging on morality risk (Table 4). Owing to there was no significant association between successful aging and mortality in the group of 75 years old and above, relevant analysis mainly on the participants aged 60–74 years old. Table 4 shows the significant correlation between successful aging and mortality only exist in females’ group with the education level of primary school and below (HR = 3.272, 95%CI = 1.019–10.507).