Although agricultural technology made remarkable progress in the world, hunger was still a serious issue faced by all human-beings. In 2020, there were as many as 720 million to 811 million people worldwide facing hunger, accounting for about 10% of the global population, and most of them were in the developing and undeveloped countries of Asia, Africa, Latin America (United Nations, 2021). To achieve the goal as stated by the United Nations by 2030 could be a huge challenge. Malnutrition or health shock in early years may bring continuous adverse effects on adult health, till the end of the life (Yao, 1999). In this paper, we investigated the long-term effects of childhood starvation on the mental health in their later life.
In recent years, the impact of life course on health attracted extensive attention from scholars in China and abroad. The relationship between the early experience of hunger and mental health in later years became a topic concerning with the emergence of poverty and hunger. Most studies found that early life experience was the basis for the development of people's whole life cycle. The seeds of many diseases in adulthood may have been planted decades ago (Warren, 2016). Malnutrition or health shock in early years would bring continuous adverse effects on adult health (Neelsen and Stratmann, 2011), for example, the metalogenesis hypothesis proposed by Barker (1998) suggested a causal relationship between health in utero and later life. Walker et al. (2007) and Victoria et al. (2008), reviewing medical evidence from developing countries in Asia, Africa and South America, suggested that, similar to malnourished fetuses, malnutrition in the first 24 months of life in children was associated with increased blood glucose concentrations, elevated blood pressure, cognitive deficits and increased odds of psychosis. Guo and Zhao (2019) believed that famine increased the risk of cognitive impairment, depression and other mental disorders in old age. Shi et al. (2012) studied the long-term cumulative disadvantage on health. Both the number of early unfortunate experiences and the duration of the events formed a long-term accumulation, especially, the duration of early starvation experience had a significant negative relationship with adult health. Moreover, women's health was more vulnerable to famine (Huang and Phillips, 2013), and it was also possible that men's death choice to cope with health shock was more serious than women's, which leaded to the long-term health damage caused by famine not likely to be fully observed in men. Shi et al. (2012) also found that the health effects of the duration of early starvation tended to long in the 50-59 age group, followed by a declining trend in the 60-69 age group, with the inflection point occurring around age 60. In addition, the health risks associated with unfortunate experiences still existed and increasing levels of education and socio-economic status generally could not decreased the health risks that accumulated when experiencing starvation in childhood.
However, the conclusions were not consistent. He et al. (2020) conducted a cross-sectional study using a sample of community-dwelling adults aged 55 and above in Ningxia Province, Western China, and found that fetal famine was associated with a higher risk of depression in later life, compared with famine in adulthood. Moreover, Dermot (2012) used the Irish Famine data and found no evidence supported that hunger was associated with an increase in the incidence rate of mental disorders such as schizophrenia and depression. Based on the research of Shi (2011), Du and Huang (2020) subdivided the health status into depression tendency of older adults, focusing on the short-term accumulation effect of unfortunate experiences. Finally, they found that the impact of recent misfortune was more significant, which indicated the time accumulation effect was not obvious. The effect of early starvation on mental health in old age may not be as obvious as that of famine in old age. The reason for this may lie in different sample selection. Du and Huang (2020) only compared the impact of negative life events that older adults went through three years ago and one year ago, rather than tracking whether the sample suffered from famine in childhood. They did not consider the impact of starvation on depressive symptoms of older adults from the perspective of long-term life cycle.
In terms of the mechanisms between early hunger on mental health of older adults, there were two main explanations. One was the physiological effect, which focused on the generation of congenital mental diseases. The "fetal origin hypothesis" held that when intrauterine malnutrition occurs, nutrition would be supplied to the head first, while the heart, blood vessels and other organs or tissues would be stunted, thus affecting the health status of adults for a long time. Neurodevelopmental disorders may be "programmed" by early life stress exposure, which used epigenetic modification to alter the brain development (Tracy et al., 2010). Biological evidence showed that congenital nervous system abnormalities were mainly related to neural tube defects (Lumey and Stein, 2011). More specifically, suffering from famine may lead to micronutrient and macronutrient deficiencies, increasing the risk of mental disorders. Protein malnutrition affected the development of hippocampus and other structures in the brain, as well as damaged the function of dopamine, serotonin and other neurotransmitters (Brown et al., 2000), laying a hidden danger for the child's future mental health. These biological conclusions provided the idea of the influence mechanism of "early experience of starvation leaded to nutritional deficiency and physiological function damage, thus inducing mental disease of older adults".
The second was the social effect, which focused on the influence of the later experience, suggesting that social support, experience accumulation and other factors were also related to depression in older adults. The social origins hypothesis suggested that early life misadventures had a persistent negative impact on health and the negative impact was not counteracted by any change in socio-economic status after childhood. Early life experiences and conditions actually reflected the characteristics of the family background, reflecting the low socio-economic status and lifestyle of the parents. Moreover, the theory of cumulative advantage, first proposed by Merton, provided the insights that the important events experienced by individuals in the course of life may have cumulative impact on the health of older adults (Cheng et al., 2020). The early famine experience led to the accumulation of disadvantages in such as education, employment opportunities and economic status, which eventually leaded to mental illness. Similarly, the stress process model suggested the occurrence of life events (such as famine) leaded to the change of chronic life stress (such as the decline of health level), and then caused the change of self-concept including sense of control and self-esteem, finally leading to the symptoms of depression (Merton, 1968).
In summary, many scholars have discussed the cumulative impact that early experiences of misfortune can have on their physical health in adulthood (Shi & Wu, 2018; Cheng & Phillips. 2013). However, less attention has been paid to the relationship between childhood starvation and mental health in later life, particularly in studies with Chinese samples. To fill these research gaps,, this study was about to investigate the impact of individuals' childhood experiences of starvation on their mental health in later life, and to specifically analyse whether this impact differs across different types of older adult groups, in order to verify whether the impact relationship proposed by foreign scholars is appropriate for the actual situation in China.
On the basis of the foregoing, we put forward the two competing hypotheses as follows:
Hypothesis 1a: childhood starvation has no impact on the mental health in later life.
Hypothesis 1b: childhood starvation has a negative impact on mental health in later life.
Some studies have found that the impact of childhood starvation on the mental health in later life was different in terms of individual characteristics (24, 25). Therefore, the following hypothesis can be proposed:
Hypothesis 2: The impact of childhood starvation on the mental health in later life is heterogeneous in different groups.