Introduction

Anxiety disorders are the most common type of psychiatric illness [1, 2]. According to a report in 2013, one in nine people in the world has had an anxiety disorder in the past 12 months [3]. In the general population, the estimated current prevalence of anxiety was between 0.9 and 28.3% and past-year prevalence was between 2.4 and 29.8% [3]. According to Burden of Diseases (GBD), anxiety plays a major role in global burden [4]. Anxiety is associated with several risk factors, including stroke [5] and diabetes [6]. Another factor in anxiety disorder is immigrant status [7].

Migration is the process by which a person moves from one culture to another for a long time [8]. In recent decades, the immigrant population has increasingly grown and the economic and social factors have influenced this trend [9, 10]. The United Nations estimates that there were about 195 million immigrants in the world in 2005 and about 10.4 million international refugees had been reported by the end of 2011 [11, 12]. A new study shows that there are about one billion immigrant populations in the world [13]. Most immigrants live in European countries and Asia and North America were in second and third places which go from developing countries to developed countries [8, 14]. Immigrant populations are exposed to higher levels of physical and mental illness [15, 16].

Because immigration affects different aspects of mental health, studies have examined mental health problems in the immigrant population, including mental illness [17,18,19], depression [20], mood, and anxiety disorders [21, 22], psychotic disorders [23] and posttraumatic stress disorder [24]. Extensive studies have examined the dimensions of mental health in the immigrant population and studies have looked at the prevalence of mental disorders in this population, as mentioned in the previous section. A recently published meta-analysis study examined suicide among immigrants and refugees [25]. According to that study, the prevalence of suicidal ideation is 16%, and the prevalence of suicide attempts and suicide plans is 6 and 4%, respectively [25]. A study of research history shows that despite the high prevalence of anxiety disorders, less attention has been paid to this category of mental illness. The only meta-analysis study that looked at the prevalence of anxiety in the immigrant population was in 2009 [7]. That study included 19 studies in a meta-analysis and the prevalence of anxiety was 28% and the prevalence of posttraumatic stress disorder (PTSD) was 47% [7].

Studies have examined health-related dimensions in the immigrant population and valuable insights have been provided in this field [25,26,27], and meta-analytical studies in this field have been able to examine the prevalence of some mental health problems, including suicide [25]. But anxiety disorders, as the most common mental health problem, need further investigation [28]. The purpose of this research is to study the prevalence of anxiety in the world’s immigrant population.

Methods

The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [29] protocol was used to perform this research. MeSH (Medical Subject Headings) keywords were extracted and their syntax is available in the Appendix, Table 3. Based on these keywords, scientific databases were systematically searched to collect articles. The search included three databases, PubMed, Google Scholar and, Research Gate, and articles in these indexes were collected until June 2020. Manual search also included reviewing related article references to increase the scope of article retrieval.

Inclusion and exclusion

The target population in the study comprised immigrants, i.e., individuals who had immigrated to another country. These included labor immigration, refugees, and asylum seekers. The psychological event for study in this population was anxiety and posttraumatic stress disorder. Anxiety included any type of anxiety disorder, including generalized anxiety, panic, social phobia, agoraphobia, obsessive–compulsive disorder, and specific phobia. The age range was considered to be at least 14 years. Populations that had been faced with severe psychological trauma were not eligible. Immigrants with physical illnesses as well as a woman during pregnancy and postpartum were not eligible. A population of fewer than 100 people, as well as studies that did not report enough information to calculate the prevalence, were not eligible. Studies with mixed outcomes were not eligible nor were studies with the same database and editorial articles.

Data extraction

As shown in Table 1, a collection of detailed information was extracted from each of the eligible articles. The following information were recoreded: the authors of the article, the country in which the immigrants lived, the type of immigration, the study design, age and sex, the sample size included in the analysis, the type of anxiety and its scale of measurement, and finally the statistical results.

Table 1 Data extracted from articles
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Qualitative measure

In measuring the quality of those studies that met the inclusion criteria of the study, three adjusted dimensions of EPHPP [30, 31] were used.

Statistical analysis

The data extracted from each of the articles are listed in Table 1. In studies where there were several subgroups for each type of anxiety, these subgroups were pooled together and the pooled number was used. An analysis was performed to assess the prevalence of anxiety disorders and PTSD. In studies that examined more than one type of anxiety in a sample, the average sample and event were used to calculate the total. In the following, I2 was used to assess the degree of heterogeneity in the studies included in the meta-analysis [32, 33]. EPHPP [30, 31] dimensions were used to assess qualitative bias as well as statistical tests to evaluate quantitative bias, as mentioned above.

Results

Study inclusion

Fig. 1 shows the screening steps of the meta-analysis. Nearly 20,000 articles were retrieved based on keywords. The screening continued in several stages to identify eligible studies. Based on screening, 266 articles were qualitatively synthesized and finally, 78 eligible articles [34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111] were identified, which are reported in Table 1.

Fig. 1
figure 1

Selection flow diagram. PTSD posttraumatic stress disorder. (From Moher et al. [29]. For more information, visit www.prisma-statement.org)

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Quality assessment

The quality of studies was assessed in three dimensions. In the selection bias dimension, most of the studies had a low and moderate bias. In the anxiety assessment method, based on the qualitative evaluation, most of the studies had a low and moderate bias. In the withdrawals and dropouts dimension, most of the studies had a low bias.

Anxiety and PTSD prevalence

Table 2 shows the prevalence of anxiety disorders. The prevalence of agoraphobia was 4% with 95% confidence interval (CI) = 3–4% (I2 = 97.5%). The prevalence of PTSD was 25% with 95% CI = 22–29% (I2 = 99.4%). The prevalence of GAD was 9% with 95% CI = 7–11% (I2 = 97.8%). The prevalence of panic disorder was 4% with 95% CI = 3–5% (I2 = 96.9%). The prevalence of OCD was 3% with 95% CI = 1–4% (I2 = 94.5%). The prevalence of social phobia was 5% with 95% CI = 3–7% (I2 = 99.1%). The prevalence of specific phobia was 8% with 95% CI = 4–12% (I2 = 98.8%).

Table 2 Anxiety and its subtypes in immigrants
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Heterogeneity

The level of heterogeneity (I2) in the total number of studies included in the meta-analysis was high, which indicates that there is a high level of heterogeneity ([32]; Table 2).

Discussion

This study aimed to investigate the global prevalence of anxiety and PTSD in the immigrant population based on a systematic review and meta-analysis. The first findings of this study showed that 4–9% of the immigrant population have different anxiety disorders, while the prevalence of PTSD was 25%. In the general population, one in nine people have anxiety [3]. The prevalence of anxiety in immigrants is almost no different from the general population. But, the findings of the current study show that the prevalence of PTSD in immigrants is high. A mechanism for the link between migration and anxiety can be the level of income, as the level of income is associated with anxiety [112]. Also, a low level of education is a factor in the increased risk of anxiety [112, 113]. Therefore, low economic and educational levels may be factors in migrating to another country and at the same time have a direct relationship with the level of anxiety of immigrants. The process of accepting immigrants, as well as the length of time it takes to be accepted, can be a factor in increased anxiety, as the study shows, the asylum process is associated with an increased risk of psychiatric illness [68, 114]. Postimmigration conditions are also important in determining the prevalence of mental health problems, as studies have shown [104, 115, 116]. Other causes of anxiety need to be addressed in determining the causes of higher prevalence anxiety; especially the lifestyle and nutrition of the immigrant population, as previous studies have shown people with smoking [117], obesity [117], and annual medical visits [118] are more likely to report lifetime anxiety disorders. Also, the reduction of resources is one of the factors that decreased after migration and can affect psychological health [119]. Among the subgroups, the highest prevalence rate was for PTSD with 25% prevalence and GAD prevalence was 8%. As the study shows, immigrants are less likely to have access to mental health services [120]. Of course, the role of stigma has also been discussed, with stigma being a major barrier to accessing psychological services in the immigrant population [121].

This meta-analysis updated the previous meta-analysis and also performed a comprehensive meta-analysis on the prevalence of anxiety in immigrants. Overall, the findings of the current study provide a perspective on the prevalence of anxiety in the immigrant population, but there are limitations. The separation of different generations of immigrants should be considered in future studies. Periods of anxiety (lifetime anxiety, 12 month, 6 month, and 1 month) are another topic that needs attention. Most of the studies included in the meta-analysis did not provide these results and this is a limitation. Residence time in the destination country is a factor that can affect the results. The issue of heterogeneity in studies included in the meta-analysis is a methodological limitation and can affect the power of the study. Of course, in the case of heterogeneity, the sources of heterogeneity should also be considered because heterogeneity has two main sources: one of which is the clinical difference and the other is statistical heterogeneity [122]. Clinical heterogeneity refers to differences in measurement methods, differences in population and subjects, and the like [122]. Statistical heterogeneity also refers to differences in quantitative methods of outcome measurement, study design, and so on [122]. Finally, another issue is the generalizability of the findings of this meta-analysis. Generalizability is limited because the study populations were from very diverse cultures that this socio-cultural-economic difference can determine the prevalence of anxiety. Another important issue is that most of the results of the studies included in the present meta-analysis were crude and in the meantime other mixed variables should be considered as possible influential variables. Therefore, in future studies, adjusted results can reduce the limit of generalizability and increase the strength of the results.

Health and clinical implications

Overall, the findings show a high prevalence of anxiety. Explanations for these different rates were provided in the previous sections. Considering the findings on the significant prevalence of anxiety and PTSD in the immigrant population and the increasing population of immigrants in recent decades, it is necessary to pay special attention to the mental health of this population. In this regard, health policies need to move towards screening this population for prevention and treatment.

Anxiety disorders are the most common mental disorders and according to the results of studies, one-third of the general population are affected by anxiety during their lifetime [28]. Also, the financial burden of anxiety disorders is very high and this has a great burden on the health of the community [123]. Anxiety disorders are effectively treatable by a range of psychological and pharmacological therapies [124, 125]. On the other hand, studies show that a significant percentage of people with anxiety disorders do not seek treatment [126]. The reasons and descriptions presented above were intended to show that the rate of health problems caused by anxiety is very high. Furthermore, given that the immigrant population is more exposed to mental health problems and their access to psychological and psychiatric health care becomes much more necessary due to economic problems and other related factors in immigrations, health-related policies need to provide wider access to mental health care. A higher percentage of people with anxiety problems should receive treatment to reduce the individual, social and economic consequences of anxiety disorders.