The study investigated the association between successful aging and mortality and education's role of moderating the effect of successful aging on mortality, we found the significant correlation between successful aging and its 5 components with mortality, meanwhile, those correlation existed gender differences.In addition, those significant association only existed in the group of female(60–74 years old) with education level of primary school and below.
For 60–74 years old group, we found that the association between successful aging and mortality in females (HR = 3.105 95%CI = 1.128–8.543), not in males.Gender differences in mortality risk were found across 5components of successful aging; the association was strongest for presence of major disease, disability, low cognitive functionand depressive symptoms in females, but for presence of major disease and disability in males. For 75 years old and above group, both males and females had not found the association between successful aging and mortality; the association was strongest for presence of major disease in males, but for presence of low cognitive function in females.
Our finding is accordance with previous studies which found successful aging was significantly associated with lower mortality. In a Korean longitudinal study of aging (2006–2014) which included 3848 participants aged 65 and above, non-successful aging older had a higher risk of mortality than successful agers (men: HR = 1.69, 95%CI = 1.18–2.43;and women: HR = 2.37, 95% CI = 1.21–4.63). Meanwhile, this study found gender differences in mortality risks across all components of successful aging (absence of major illness, freedom from disability, no depressive symptoms, active social engagement, satisfaction with life, high cognitive function, high physical function). A study(2 year followed survey)from longevity areas of China focusing on the relationship between successful aging index (assessed by self-rated health, depressive symptoms, cognitive function, disability, and physical activities)and the survival status included 2296 old people (65 years old and above). According to this research, the mortality rate in the successful aging group was lower than non-successful aging group, the death rate in successful aging group reduced by 38%(HR = 0.62, 95% CI = 0.49–0.79). Considering the definitions of successful aging varied from researches, we cannot directly compare those previous available studies with ours. However, from another perspectives, it is proved that achieving successful aging is crucial for lowering mortality and improving life-expectancy, which could support our study.
We can conclude that aging successfully may be beneficial for lower the risk of mortality, but components of successful aging had different contribution to mortality varying from genders.Some studies indicated this gender difference may result from biological, genetic, and social variations [21–24]. Our study showed that the significant association between successful aging and mortality only existed in females (60–74 years old). On the one hand, possible explanations for the phenomenon is that the association between all components of successful aging (except "Active social engagement in life") and mortality was significant in females (60–74 years old), however, there only found significant association between partly components of successful aging ("Major disease" and "Disability") and mortality in males, as a result, the overall effect of successful aging on mortality in males was diminished. On the other hand, possible explanations for the association between the specific components of successful aging ("Depressive symptoms" and "Cognitive function") and mortality may be weaker in males than females might be that females may have greater and more prolonged hypothalamic-pituitary-adrenal (HPA) response to challenge at older ages than males.That is to say,post-menopausal women are at increased risk of exhibiting greater and more prolonged HPA activation, which may contribute significantly to the increased risksamong such post-menopausal women for chronic disease, depression, disability and so on,previous researches had proved those diseases are associated with higher mortality.
Meanwhile,the association mentioned above diminished with increasing age, that is to say, we cannot observe similar correlation at the 75 years old and above group among males and females.Potential explanation for the declines in the effects of successful aging on mortality with age is that physiological factors gradually become the prominent contribution factors more than others such as diseases, behaviors and so on for the death of people aged 75 years old and above group.
It is the first longitudinal study using national cohort data to research the educational effects on the association between mortality and successful aging, the study showed that the effect only existed in females aged 65–74 years old group with lower education. On the one hand, focusing on the role of education rather than SES which usually was a comprehensive concept (including education, occupation, income, social class, physical health and so on) provides us a precisely perspective to understand the connection between successful aging and mortality. On the other hand, some studies had found that the effect of education on mortality is stronger in young old than in oldest old, lower education population had less possibility to access to more health resources which are related with good health and survival[27, 28].