1. Introduction
In modern society, fierce job competition and tense interpersonal relationships can easily cause mental health problems among professional people. Mental health refers to a state of psychological functioning in which an individual has no mental illness or abnormality, is well adapted to society, has a perfect personality and ability, and can fully realize their potential [
1]. The physical and mental health of the population and the ability to be socially well-adjusted can directly affect the survival and development of enterprises as well as national social stability [
2]. About 450 million people worldwide are reported to suffer from mental illness, and at least one in four families suffers from psychological and behavioral disorders. Approximately 25% of the UK population experiences mental disorders every year [
3]. Annual incidence of mental disorders in Ghana is 13% [
4]. The prevalence of mental disorders in China is 12% [
5], while the lifetime prevalence of mental disorders in West Africa is 12.1% [
6]. According to research data, the economic burden of mental illness was about 2.5 trillion US dollars in 2010, and it is estimated that the cost will increase to 6 trillion US dollars by 2030 [
7], which accounts for about 3–4% of gross national product (GNP) in developed countries. However, most of the social burden of mental health problems is not related to the cost of treatment, but to the reduction in human capital and productivity [
8].
At present, research on the mental health problems of occupational groups mainly include teachers, medical personnel, skilled workers, oil workers, police, etc. Studies have found that long-term excessive pressure or harsh working environments aggravate the occurrence of mental illness [
9,
10,
11,
12,
13]. Recent research on the influencing factors of mental health mainly analyze the relationship between gender, age, education, marriage, physical health, and other population characteristics and mental health (e.g., Yu Shanfa [
14], Yu Xiaoxia [
15], Qiu Xingyuan et al. [
16]). Some scholars also found that work time, work status, and work arrangements were correlated with psychological problems. Excessive working hours, frequent shift work, and high workloads lead to a series of negative emotions [
17,
18,
19]. The causes of psychological problems are numerous and are often a combination of multiple factors. Therefore, by evaluating the health risk factor, some scholars have studied the probability of disease occurrence in the environment by examining risk factors, as well as the change in the disease occurrence risk factor in response to changes in unhealthy behaviors and by eliminating or reducing risk factors [
20].
Health risk appraisal (HRA) is a technical method that is employed to study the quantitative dependence and regularity between risk factors and the incidence of chronic diseases or deaths [
21]. HRA mainly examines the impact of various risk factors in terms of the occurrence and development of diseases in the production environment, lifestyles, and medical and health services. By taking effective measures, risk factors that can be changed by intervention, such as workload (e.g., working hours, complexity, shift work), interpersonal relationships (superiors and subordinates, colleagues), and poor working environments (noise, dust, chemical poisons), have been proven to reduce the risk of disease. Studies [
22,
23] have confirmed that the evaluation of health risk factors plays a positive role in disease prevention.
With the rise of molecular genetics, more and more researchers are beginning to pay attention to the effect of gene polymorphism on mental health. It was found that monoamine oxidase A (MAOA) mainly acts on the limbic system which is associated with higher cognitive functions such as emotional regulation. The gene, located on the X chromosome, degrades neurotransmitters such as serotonin, dopamine, and catecholamines in the human brain and affects the psychological state of the individual by regulating the level of neurotransmitters in the brain. Yu et al. [
24] proved that either low activity or lack of MAOA contributed to an ineffective degradation of excessive serotonin, which was the direct cause of depression. A study explored the relationship between the
MAOA gene and alcoholics with depression and anxiety by examining the polymorphism of the promoter region of the
MAOA gene in the blood of German male and female alcoholics, and found that the
MAOA gene was closely related to the incidence of anxiety and depression among alcoholics [
25]. In recent years, epigenetic research has made great advancements. The researchers believe that epigenetic modifications provide a means of explaining the influence of environmental factors on gene function. In addition, epigenetics can also offer a theoretical basis by which to explain the inconsistencies of a large number of studies on the association between mental health problems, such as the different transcription efficiency caused by different epigenetic modification states of gene promoters [
26]. DNA methylation is one of the more thoroughly studied mechanisms of epigenetic modification. It is a heritable and precise form of gene regulation provided by eukaryotes with cytosine methylation to assist gene silencing [
27]. Methylation of transcription factor binding sites does not significantly affect the specific binding of transcription factors, while methylation of CpG sites in adjacent sequences can significantly reduce the binding activity of transcription factors [
28]. The
MAOA gene has two CpG islands, and the differential methylation status of CpG islands can dynamically affect gene expression and the synergistic effect of other potential transcription factors, resulting in different pathogenicity [
29,
30].
The onset of psychological problems is influenced by genes, environment and epigenetics. However, most of the current studies focus on the polymorphism of the
MAOA gene variable number tandem repeat (VNTR), and the majority of studies are related to behavior, such as aggressive behavior and criminal behavior [
31,
32], and they lack consistent results. Therefore, this study selected the
MAOA rs6323 locus and
MAOA rs 1137070 locus to study the genes implicated in psychological problems and analyzed the correlation between both loci and psychological problems. In addition, the DNA methylation level of the
MAOA gene in the mental health group and the abnormal group was compared, to explore the relationship between DNA methylation mechanism and mental health.
4. Discussion
With the transformation of the medical model, mental health has received increasingly more attention. One study showed [
42] that psychological problems are highly correlated risk factors for sleep disorders. Stress, anxiety, depression, and other negative emotions reduce the working ability of the occupational population, causing absenteeism, job burnout, and other phenomena, and seriously affects the quality of life of the occupational population [
4,
43,
44]. The causes of mental health problems are various, and include the environment, genes, and heredity [
5,
6].
The results of this study found that there were differences in the incidence of psychological disorders among different ethnic groups, ages, types of work, working years, professional titles, shift work, and marital status. The incidence of psychological abnormalities was the highest in the group aged between 30 and 45 years. The reason for this finding may be that most people in this age group are married, they need to take care of children and the elderly in their lives, and they are also experiencing a period of career progress in their work, with substantial work pressure [
45]. The incidence of psychological abnormalities was higher among oil extraction workers than those who engage in other types of work. Due to the special nature of oil production and poor work planning, it is difficult to carry out the work in an efficient and orderly manner. At the same time, because oil extraction work is carried out in the field, the natural environment is harsh, the living conditions are difficult, and there is less communication with the outside world, so there is no means of alleviating work-related pressures [
46]. The incidence of psychological abnormalities was highest among workers with 10 to 20 years of working experience. At this stage, most workers were in important positions or leadership positions, and they assumed more responsibilities and obligations, so there were additional factors that caused mental health problems. With the increase in working years, people have to confront various sources of tension arising from their work and personal life, so negative emotions can easily contribute to the occurrence of mental health problems [
47]. The incidence of psychological abnormalities rises in line with an increase in the status of professional titles. People with high ranking professional titles tend to experience a higher degree of stress and psychological problems [
48]. The incidence of mental abnormalities among people whose job requires shift work is significantly higher than that observed among people who work a fixed day shift. Multiple studies have found that shift work can affect sleep, work ability and the mental health status of those in the workforce [
49,
50]. The results of a meta-analysis on shift work and mental health [
51] showed that shift work is closely associated with an overall increased risk of adverse mental health outcomes (ES = 1.28; 95% CI = 1.02, 1.62), especially for depressive symptoms (ES = 1.33; 95% CI = 1.02, 1.74). Unmarried people have the lowest incidence of psychological abnormalities, while divorced or widowed people have the highest incidence of psychological abnormalities. Unmarried people do not need to raise children or take care of life chores, they live independently, and experience less financial pressure, so they tend to maintain a good mood and a better mental health status than married people. People who are divorced or widowed may be more likely to experience mental health problems as a result of a failed marriage or the pain of losing a loved one. Domestic scholars Liao Siqi et al. [
52] also believed that marital status had a significant impact on tendencies for depression after analyzing the tendency to develop depression among 1837 oil workers in the Panjin area, and divorced oil workers scored the highest for depression tendency.
Large-scale epidemiological surveys in various countries around the world [
53,
54] showed that the odds ratio (OR) of residents of different races and from different regions varied greatly. When different risk factors co-existed, the risk of psychological abnormalities significantly increased. The results of this study found that different sexes had different risk factors for mental health: The risk factors of male mental health included age >45-years-old (relative to ≤30-years-old), shift work, moderate, and high occupational stress, high effort/low return, while the risk factors of female mental health included age >45-years-old (relative to ≤30-years-old), high occupational stress, and high effort/low return. In respect to shift work as a risk factor for the mental health of men working in desert oil, the risk scores of different age groups were 1.214, 1.172, and 1.369, respectively. If the shift could be changed to a fixed day shift, the risk scores could be reduced to 0.560, 0.623, and 0.512, respectively. Nascimento et al. [
55] recently conducted a study of 231 nurses who worked shift work and found that shift work can result in negative emotions and lead to sleep problems. Highly intense work and intense competition can easily lead to stress. Many studies have shown that stress is an important factor affecting mental health [
48,
56]. As a risk factor of mental health, the risk score of occupational stress among different age groups reached 5.081, 4.767, and 3.278 for males and 3.252, 2.801, and 2.793 for females, respectively. If the source of stress can be reduced, the degree of occupational stress can be reduced to moderate stress. The risk scores of men can be reduced to 4.712, 3.916, and 2.724, respectively; the risk scores of women can be reduced to 2.972, 2.654, and 2.778, respectively. If the stress level can be reduced to low stress, the risk scores of men can be reduced to 2.840, 2.844, and 2.123, respectively, and the risk scores of women can be reduced to 1.783, 1.730, and 2.081, respectively. Foreign studies reported [
57] that occupational stress can, to a certain extent, contribute to the development of psychological diseases and cardiovascular diseases. Occupational stress can affect the mental health of oil workers, generating or exacerbating anxiety and depression [
58,
59,
60]. The risk scores of ERI among different age groups were 1.353, 1.274, and 1.264 for males, 1.538, 1.496, and 1.694 for females, respectively. Desert oil workers do not receive a corresponding return for their work efforts, which may lead to job burnout and a feeling of dissatisfaction with life, as well as anxiety, depression, and other psychological conditions. If the efforts and returns can be balanced, the risk of psychological abnormalities can be greatly reduced. Shift work, occupational stress, and pay return are all contributing factors. If these contributing factors are not addressed, the situation is bound to diminish the working ability and efficiency of employees and is more likely to result in workplace accidents [
48].
In this study, it was found that the somatization factor score of TT genotype was higher than that of the GG group in regard to different psychological health groups of desert petroleum workers with rs6323 locus of the
MAOA gene. The rs1137070 was not found to be associated with mental health problems. Aslund et al. [
61] found a significant association between rs6323 polymorphism of the
MAOA gene and anger-related traits in a controlled study on suicidal tendencies. Cao Cong et al. [
62] concluded that the polymorphism of the
MAOA gene T941G and peer aggression interact with adolescent male depression, and the genetic variation of the
MAOA gene may affect the antidepressant treatment effect of depressed patients [
63,
64]. Tadic et al. [
65] believed that the
MAOA gene was related to anxiety disorder, and
MAOA polymorphism was related to female anxiety disorder, which was not found in male patients. This study compared the methylation level of
MAOA gene DNA methylation at different sites in the group with participants with psychological problems and found that the methylation level of the group with psychological abnormalities was lower than that of the group with psychological normality. DNA methylation influences gene expression by interacting with transcription factors or changing the chromatin structure, regulates biological genetic information at the epigenetic level, and plays an important role in growth and development [
66]. Studies suggest that mental illness is caused by the interaction between genes and the environment, and DNA methylation is closely related to the occurrence of mental illness [
67,
68]. Domschke et al. [
69] demonstrated that panic disorder is related to the hypomethylation level of the
MAOA gene, which is consistent with the results of this study. In their study on CBT treatment of panic disorder, Ziegler et al. [
70] found that the methylation level of the
MAOA gene in patients who participated in the treatment increased after six weeks of treatment, suggesting that there was a negative correlation between the severity of panic disorder symptoms and the methylation level of the
MAOA gene. Teroganova et al. [
71] also found that methylation levels in male schizophrenia patients were lower than those in the control group, but no difference was found in women.