Heart disease refers to a set of heart problems, including but not limited to coronary heart disease, heart attack, congestive heart failure, and angina . Heart disease is the top health problem in the Chinese population. The morbidity of heart disease in adults aged 60 years or older is generally higher than that in middle-aged adults . It is important to note that the pathogenic causes of heart disease usually begin in early life, especially during childhood [3–5]. According to a report on cardiovascular health in China, around 20% of adults older than 18 years old have heart disease . Heart disease accounted for more than 40% of disease-related deaths . It is the top cause of mortality, even higher than cancer and cerebrovascular diseases.
Heart disease not only has adverse impacts on individuals’ physical health and social functioning, but also is a risk factor for Alzheimer disease and other types of dementia [7, 8]. Moreover, given the lifestyle changes and population aging in many developing countries, the average age of individuals who are diagnosed with heart disease is decreasing . The prevalence of heart disease is predicted to continue to rise in the next few decades. At the same time, hospitalization costs due to heart disease are also increasing rapidly. Under such circumstances, China has encountered great social and economic burdens due to heart disease. There is a urgent need for preventive strategies and interventions that promote heart health and healthy aging among community-dwelling older adults.
Previous research identified a range of individual-level social and health factors related to heart disease [10–14]. Specifically, recent Chinese studies identified significant associations between unhealthy behaviors (e.g., smoking) and heart disease [10, 11, 13]. Furthermore, overweight and obesity were found to be the main risk factors for hypertension and dyslipidemia, which further increase the risk of heart disease [1, 15]. Physical inactivity is another risk factor for heart disease. Decreasing physical functionality may increase the risk of overweight or obesity, hypertension, and dyslipidemia [1, 16]. Finally, mounting evidence indicates that socioeconomic status (SES), social support, and negative life events have accumulative influences on heart disease, and they should be examined from a life course perspective [5, 17, 18].
Abundant evidence indicates that childhood conditions are associated with health outcomes in later life, including functional health status, mental health status, cognition, chronic diseases, and mortality [19–21]. Some studies, for example, suggested that early life conditions play an important role in influencing functional health status in later life in developing countries . Another Chinese study found that early life conditions affected cognitive function in middle-aged and older adults . Furthermore, children from poor families were more likely to have low educational attainment, low income, and poor health status in later life than their counterparts from rich familes .
Risk factors and behaviors related to heart disease can be traced back to childhood, and the effects might accumulate over time and influence adulthood and even older life [2, 5, 23]. Growing studies have investigated different sets of risk factors and behaviors linked to heart disease at different life course stages [2, 24]. However, only a few studies explored the relationships between childhood conditions and heart disease in the context of China. Among the limited number of relevant studies, the majority focused on the effects of SES on heart disease in later life. Few studies have considered other childhood conditions such as health conditions and access to health resources [5, 25, 26]. Therefore, the present study focused on multiple childhood conditions, including childhood SES, childhood self-rated health (SRH), severe illness in childhood, and access to health resources nearby in childhood [5, 22]. Given the trend toward younger people being diagnosed with heart disease in China, this study aimed to examine early life risk factors of heart disease among middle-aged and older populations.
Early-life Conditions And Heart Disease In Later Life
The pathways linking childhood conditions to heart disease in later life can be both direct and indirect. Two main theoretical perspectives were used to explain the association between childhood conditions and health outcomes in later life: the latency model and the pathway model [27–30]. The latency model suggests that childhood circumstances have a direct impact on health outcomes in adulthood and later life through influencing individuals’ health trajectory patterns [21, 31]. In other words, childhood adversities such as low SES, undernutrition, and severe illness may permanently alter individuals’ trajectories of health throughout the life course, even after controlling for conditions in adulthood. For instance, poor maternal nutrition in childhood could weaken individuals’ immune systems and alter the function of important organs associated with blood pressure, lipid regulation, and insulin . In turn, this could increase the risk of chronic diseases in adulthood and later life, such as heart disease and diabetes [29, 32, 33].
Furthermore, the pathway model argues that childhood circumstances could indirectly affect health outcomes in later life. Childhood adversity often has adverse impacts on health outcomes in later life through influencing individuals’ educational achievement and employment in adulthood [20, 33]. Poor childhood conditions could increase the risk of chronic diseases in adulthood (e.g., hypertension and heart disease), which in turn could have long-term adverse impacts on their cognitive function and social competence and further lead to relatively low levels of educational achievement, occupational status, and income in adulthood [5, 20, 33]. In addition, low SES in childhood and adulthood might be associated with poor living environment and living conditions, which can further affect individuals’ educational achievement and health outcomes in later life [29, 33]. Childhood conditions are also associated with health-related behaviors. Individuals raised in families with low SES are more likely to adopt unhealthy behaviors, such as smoking and alcohol use, which can affect health outcomes in later life [19, 34]. It is important to note that the latency model and the pathway model are not mutually exclusive. Both processes could coexist and influence health outcomes in later life.
The literature has a few major gaps concerning childhood conditions and heart disease and other health outcomes in later life. First, many previous studies used selective samples (e.g., oldest-old adults and samples from hospitals). Therefore, the empirical generalization of the findings are limited. Second, although different childhood conditions might affect health in later life differently, the majority of studies only used childhood SES to represent childhood conditions. Third, most previous studies were conducted in developed countries; relatively less is known about whether the association between childhood conditions and heart disease exists in developing countries. It is important to note that the childhood conditions of a large proportion of current middle-aged and older cohorts are harsher than their counterparts in developed countries . Therefore, new empirical evidence is needed to inform policy and intervention developments in developing countries, especially in China, which has the largest middle-aged and older population in the world.
China has undergone dramatic transitions, both socially and economically, mainly due to economic reforms and rapid urbanization in the past few decades. Before the economic reforms implemented in the late 1970s, China had undergone the Great Chinese Famine (1959–1961) and the Great Cultural Revolution (1966–1976). Thus, many middle-aged and older adults born before 1970 experienced unrest and upheaval during childhood. After the economic reforms, millions of Chinese adults’ standards of living have improved significantly . Although improved living standards are important in influencing health outcomes in later life, this may not completely offset the disadvantages of childhood conditions on health outcomes in later life.
In the present study, we used the China Health and Retirement Longitudinal Study (CHARLS) to examine whether childhood conditions are associated with the onset of heart diseases in later life among middle-aged (45–59 years) and older (60 years or older) adults in China. CHARLS is a nationally representative survey of the population aged 45 or older. A life history survey was conducted in 2014, so CHARLS is suitable to examine the association between childhood conditions and heart diseases through a life course perspective. We extended previous literature by investigating the effects of childhood SES, childhood SRH, illnesses in childhood, and access to health care resources in childhood on heart disease in later life. Furthermore, we tested the roles of illness status, access to health care resources, body mass index (BMI), fuctional loss, and hypertension in adulthood as conditions in later life. At the same time, we controlled for demographic characteristics and health-related behaviors. It is important to note that China is a two-tier society. This means that in China, citizens living in urban and rural areas hold different household registration types: nonagricultural and agricultural, respectively. Compared to citizens with an agricultural household registration, those with a nonagricultural household registration status usually have more educational opportunities and access to better medical resources and social welfare systems [36–38]. Therefore, we added household registration status as a control variable.
In summary, poor living conditions, low SES, and poor health in childhood could have direct and indirect negative effects on health outcomes in later life. Findings regarding the association between childhood conditions and heart disease in later life are important for policy and intervention implications and could further help China achieve healthy and active aging. Based on the literature and theoretical models previously discussed, we proposed the following hypotheses about the relationship between childhood conditions and heart disease in later life among Chinese older adults:
Socioeconomic status in childhood is associated with heart disease in later life.
Childhood self-rated health is associated with heart disease in later life.
Severe illnesses in childhood are associated with heart disease in later life.
Access to health care resources in childhood is associated with heart disease in later life.