In recent years, with the increasing number of elderly populations, their health problems have attracted more and more attention. It is not only the basic physical health that affects the quality of life and health level of the elderly, but also mental health is becoming an important factor . If the spiritual needs of the elderly are not met, it will produce loneliness, depression, and accelerate the physical and psychological aging of the elderly. Mental health problems will induce depression, Alzheimer's disease, and other psychological diseases [2, 3]. In serious cases, mental health problems may even increase the risk that older adults would attempt or commit suicide. As older adults retire, they have less social participation, and their spiritual needs will be more difficult to be satisfied socially. At present, the common psychological problems of the elderly include anxiety, depression, hypochondriasis, obsessive-compulsive disorder, diet and sleep disorder, cognitive disorder, interpersonal sensitivity, alcohol dependence and so on . If the government does not intervene, those mental health problems can lead to serious consequences for the whole society.
Previous studies have found that mental health status of the elderly is related to emotional sensitivity factors, but few studies pay attention to the impact of positive psychology from a holistic view on the mental health of the elderly [5–7]. China's increasing urbanization has not only brought convenience to the elderly, but also brought great challenges. These challenges are like the socio-cultural challenges experienced by Americans at the beginning of 20th century. At the beginning of 20th century, American historian James Adams first created the word "American Dream" in Epic of America, which is based on this background. In 2013, China also put forward the "Chinese dream". These dreams are the highest needs of human psychological development and the spiritual pillar of unity, encouragement, and support for social progress . The connection between the Chinese dream and the American dream is the positive psychology behind the national dreams. The importance of positive psychology to China is not only the promotion of history, the inevitable requirement of development, the voice of the Chinese people, but also the responsibility of China’s healthy aging.
Compared with positive emotions, commitment, relationships and achievements, there were few studies on the impact of positive psychology on the mental health of the elderly. Like achievements, positive psychology is a promoting factor, which will make the elderly more resilient when facing difficulties in life [9–11]. Scholars have explored the impact of positive psychology on mental health among people. The theoretical basis of positive psychology is Darwin's theory of evolution. In his theory of evolution, Darwin pointed out that human psychology is the result of long evolutionary history. Natural selection and sexual selection are the main evolutionary processes that produce these psychological mechanisms. The meaning of the selected psychological mechanism is to be conducive to human survival and reproduction. Human evolutionary choice makes human beings have positive nature, empathy, self-control, moral sense, and reason, like learning, love creation, good at imagination and willing to plan the future. It also makes human beings have love, a sense of responsibility, understand communication and cooperation, have the ability of aesthetic and image thinking, and improve their mental health status [12, 13]. Furthermore, humans have one of the oldest nerve channels, called the vagus nerve. The vagus nerve governs most of the organs of the respiratory and digestive systems, as well as the feeling, movement, and gland secretion of the heart. The new research of positive psychology has found that the vagus nerve is related to prosocial behavior, morality, and positive experience of happiness [14–16]. Research on the elderly found that when people see noble and beautiful things, they will feel a positive force because of the opening of the vagus nerve . Moreover, a study argued that when people are positive, their self-identity will be improved and they will be more willing to design and pursue life goals, so that their intellectual resources will be improved and their ability to solve problems, think about problems and create problems will be strengthened . The study of Song et al. (2019) focused on the efficacy of psychological capital intervention (PCI) for depression from the perspective of positive psychology supported this conclusion ; the scholars agreed that positive psychology makes people produce positive emotions, including pride, calm, gratitude, satisfaction, interest, pleasure, hope, curiosity, and love. Positive emotion is an important ability that can help improve people's quality of life and happiness index. It is a valuable renewable resource. In addition, some studies summarized the moderating role of personal value between positive psychology and mental health [20, 21].
In Chinese society, after economic reform in 1978, the fierce competition of the free market economy to a large extent urged the individual atomized . These individuals have lost the protection of the original planned economic unit system, and all social problems have been transformed into personal viability and let individuals bear these problems alone. In the 1980s, personal independence was once a liberation force admired by everyone, but now it has become a huge pressure that vulnerable individuals can't bear. After the mid-1990s, when the individualism ideology began to envelop the market, it also participated in the re-shaping of people, which made people equip with more independent consciousness . Entering the 21st century, with the development of urbanization and the development of socialist market economy with Chinese characteristics, individualism has become an irreversible trend in Chinese society
Individualism can positively or negatively regulate the relationship between positive psychology and mental health. On the one hand, individualism can play a negative regulatory role. Under the catalysis of individualism, due to the lack of responsibilities and obligations for the public interest, individuals have no sense of belonging to the community. Especially for people born in and after 1980s, economic reform has made them realize that personal interests had priority over collective interests, and they can't find an organic connection with public life and public community, so they can't bear the corresponding responsibilities required by society, which may lead to their lack of positive psychology and reduce their mental health . Besides, individualism may degenerate into more and more intense anxiety. The emergence of solipsistic individualism is related to the disappearance of certainty and security. When various communities acting as protectors are dissolved, people may lose their sense of security, and this will damage their mental health status . On the other hand, individualism plays a different role for people born in 1960s and before. These people are the elderly in China. They experienced famine and poverty in the collectivist period. Individualism brings them hope that people can actively pursue life happiness. Economic reform in 1980s made them more aware that Individualism can play a positive role of initiative and participation in personal life and social interaction. This also means that individualism promotes people's own welfare . In Chinese context, old people with individualism have a more positive attitude to face life challenges and have better resilience and mental health status in the transitional society . Therefore, for the elderly in China, individualism is more likely to promote the relationship between positive psychology and mental health.
In summary, as fewer empirical studies have explored the impact of positive psychology on the mental health status of older adults in China, in the context of the rise of individualism. To fulfill this gap, this study aims to explore the relationship between positive psychology and mental health for the elderly in China, using the 2017 wave of Chinese General Social Survey (CGSS) data. The results of this study could shed light on future studies concerning the effect of positive psychology on mental health in transitional society.