Elsevier

Sleep Medicine Reviews

Volume 41, October 2018, Pages 78-86
Sleep Medicine Reviews

Clinical review
The impact of ethnicity on the prevalence and severity of obstructive sleep apnea

https://doi.org/10.1016/j.smrv.2018.01.003Get rights and content

Summary

Obstructive sleep apnea (OSA) is a common disorder associated with multiple adverse health consequences and its prevalence is increasing in parallel with rising obesity trends. Early support for ethnic differences in OSA prevalence and severity has been derived from studies of relatively homogenous ethnic groups. However, between-study comparisons are problematic given differing methodologies. Recent large inter-ethnic studies examining different ethnic populations using standardized protocols support the notion that Chinese have an increased OSA prevalence and severity compared to those of European descent. Although the evidence is less clear, some data suggest that Hispanic/Mexican Americans also show higher rates of OSA, while OSA prevalence in African Americans is not dissimilar to that of populations of European ancestry. Of the anatomical traits underlying differences in OSA prevalence and severity between ethnic groups (i.e., obesity, fat distribution, and craniofacial structure) obesity appears to be the most important. The effect of ethnicity on non-anatomical factors (i.e., upper airway muscle responsiveness, arousal threshold, and loop gain) responsible for OSA severity and potentially prevalence is currently unknown and needs further research.

Introduction

Obstructive sleep apnea (OSA) is a common condition characterized by repeated upper airway obstruction during sleep, recurrent oxygen desaturation, and frequent arousal from sleep [1]. Untreated OSA is often associated with excessive daytime somnolence (EDS), motor vehicle accidents and neurocognitive impairment [2]. Furthermore, there is evidence for a causal link between OSA and cardiovascular disease (CVD) [3], [4] and all-cause mortality [5], [6], [7]. Epidemiological studies demonstrate that important differences in the prevalence, severity and expression of OSA may exist between different ethnic groups ∗[8], ∗[9], ∗[10], ∗[11], ∗[12], ∗[13], ∗[14]. Understanding the phenotypic traits that underlie these ethnic differences, and the extent to which they contribute to OSA prevalence and pathogenesis across ethnic groups, is important to plan and implement health care delivery for OSA between and within ethnically diverse populations.

The topic of ethnicity and OSA was first reviewed by Villaneuva et al. in 2005 [15]. At that time the authors acknowledged several challenges associated with comparisons of OSA prevalence and phenotypic traits across studies of single ethnic groups. Difficulties include widely different protocols and methods used to define the presence and severity of OSA and craniofacial characteristics across studies. For example, the diagnosis of OSA from polysomnography (PSG) depends heavily on the scoring criteria used [16], which in turn will strongly influence prevalence estimates. Multiple scoring rule changes over time have made it difficult to compare OSA prevalence between studies. Some epidemiological studies have relied on self-reported questionnaires for diagnosis of OSA [17], [18], [19] or use of in-home, limited channel tests involving respiratory and oximetry signals without sleep measurements ∗[11], ∗[14], further impacting the reliability of OSA prevalence estimates.

Villaneuva et al. [15] concluded that the overall prevalence of OSA was broadly similar across those of European ancestry, Asian and Indian populations, and ranged from 1.3 to 7.5% in men and 2–3.2% in women. Based on limited inter-ethnic data, the authors concluded that African–American ethnicity may be a significant risk factor for OSA compared to those of European ancestry. The observation of increased OSA risk was also seen among American Indians and Hispanics, but was largely explained by complex obesity parameters.

Since Villaneuva et al.'s [15] initial review, several large epidemiological and cephalometric studies, each comprising multiple ethnic groups, have examined the influence of ethnicity on OSA prevalence, and relationships with obesity and craniofacial structure. The purpose of this review is to examine the current state of evidence regarding the prevalence, severity and expression of OSA across different ethnic groups; including the potential role of craniofacial characteristics and body habitus differences in understanding how ethnicity affects OSA, and how symptoms associated with OSA differ across ethnic groups.

To assess the effect of ethnicity on OSA prevalence, systematic searches of bibliographic databases up to December 2016 were conducted by first author KH including MEDLINE, PubMed, PsycINFO, the cumulative index to nursing and allied health literature (CINAHL), Scopus, ProQuest and cochrane central register of controlled trials (CENTRAL). We searched Medline, Embase, and the CENTRAL to identify relevant studies from inception to 25 July 2017. We used database specific subject headings (such as MeSH terms) and free text terms to search for potentially eligible studies (Appendix 1). We also performed similar searches to identify studies that have evaluated inter-ethnic craniofacial differences using the same objective sleep analysis techniques and craniofacial measurements from inception to 3 August 2017 (Appendix 2) to explore potential mechanisms for the differences in OSA prevalence and severity between ethnic groups. The articles were screened by title and abstract, and selected for full text review if they met the following inclusion criteria: multi-ethnic epidemiological/cohort studies, population studies, documented OSA prevalence and/or prevalence of patients at risk for OSA, articles in English and adult participants in studies using PSG or other objective forms of sleep assessment for OSA diagnosis. To minimize the impact of methodological differences and risk of bias introduced by individual studies assessing single ethnic populations, this review was restricted to inter-ethnic community cohort studies, in which the prevalence and/or severity of OSA was reported for each ethnic group and derived using the same sleep study recording techniques, scoring methods and disease definitions contemporaneously in use around the time of each study (see more details below). Within the main papers identified, we also reviewed the impact of ethnicity on the two main symptoms of OSA (snoring and daytime sleepiness).

The presence and severity of OSA are primarily defined using the apnea hypopnea index (AHI), or the respiratory disturbance index (RDI), which quantifies the frequency of obstructive events per hour of sleep or recording time. However, according to the third edition of the international classification of sleep disorders (ICSD) [20], the diagnosis of OSA requires either signs/symptoms or an associated medical or psychiatric disorder (e.g., hypertension, coronary artery disease, atrial fibrillation, congestive heart failure, stroke, diabetes, cognitive dysfunction, or mood disorder) coupled with ≥5 apnea and/or hypopnea events per hour of sleep during PSG. Alternatively, AHI ≥ 15 events per hour satisfies the criteria for OSA in the absence of symptoms [20]. In this review we predominantly focus on OSA prevalence defined on the basis of an AHI ≥ 15 events per hour using ICSD-3 criteria [20]. However, given that respiratory signals and criteria for defining apneas and particularly hypopneas have evolved considerably over time, and that this may confound comparisons of OSA prevalence and severity between studies, caution is warranted in the interpretation of potential inter-ethnic differences reported.

Ethnicity refers to a group of individuals sharing a common racial and/or cultural background ∗[15], [21], and in medical research is typically applied to the investigation of ethnicity dependent disease distributions and for health service provision planning [15]. Most ethnicity based research studies, including those selected for this review, rely on self-reported ethnicity or researcher based cultural assumptions at the time of study [22]. We acknowledge that there are several complex challenges for defining ethnicity in epidemiological/medical research, and that the relative merits of any specific definition inevitably remain debatable. In the studies selected for this review, variability exists in how individual study participants rated their own cultural identity, as well as how researchers report and define different ethnic groups, especially for studies spanning a period of time when definitions of ethnicity may have changed. For instance, some studies reported Europeans as “White” or “Caucasian” ∗[9], ∗[10], ∗[11], ∗[13], ∗[14] while another study has used the term “Caucasian/White” [12]. Variable terminology was also seen when defining Hispanics and Mexicans ∗[8], ∗[9], ∗[11], ∗[12] and African Americans ∗[8], ∗[10], ∗[12], ∗[13]. As such, for the purpose of this review, we have chosen to use “European ancestry or Europeans” to uniformly describe the diverse nomenclature used in other studies, including “Caucasians, Whites and European ancestry”. We have also selected “African American” to define “Black” or “African American” and “Hispanic/Mexican Americans” for “Mexican Americans and participants with a Hispanic background”.

Section snippets

Ethnicity and the prevalence of OSA

Our literature search yielded 1588 potentially relevant citations. Diagnostic criteria for OSA varied widely between studies with respect to definitions of apnea and hypopnea, types of diagnostic tools used and symptoms (e.g., snoring, witnessed apneas, daytime somnolence). Eight inter-ethnic studies met the selection criteria for inclusion in this review and are summarized in Table 1. Eight studies reported prevalence and severity data across OSA severity groupings, which, for consistency,

Ethnicity and symptoms of OSA

Reporting of symptoms by patients with OSA may be affected by their level of education and cultural differences in the interpretation and perception of OSA and its impact on health. Furthermore, data collected from specialist clinics (i.e., clinical/non-community samples) may not be reflective of symptom differences between community ethnic groups, particularly when there may be variable levels of access to health care across countries. Thus, to assess the effect of ethnicity, we examined two

Role of obesity on ethnicity-specific differences in OSA prevalence

Obesity appears to be the dominant factor explaining the observed differences in OSA prevalence and severity across ethnic populations. Obesity is a well-recognized, major public health problem and BMI continues to be the most widely used measure of obesity [26], despite its limitations. The prevalence of obesity [27] and the pattern of adiposity vary between ethnic groups [26], [28] and this may be an important contributing factor to the observed differences in OSA prevalence and severity

Role of craniofacial characteristics on ethnicity-specific differences in OSA prevalence

Craniofacial morphology is being increasingly recognized as an important phenotypic factor in the pathogenesis of OSA. Craniofacial anatomic features that are considered to be associated with OSA include skeletal structures (mandible, maxilla, cranial base, hyoid, face and head position) and soft tissues (tongue, soft palate, parapharyngeal fat pads, lateral pharyngeal walls, upper airway) [29], [35]. The main features that are believed to predispose an individual to OSA include a small

Non-anatomical OSA phenotypes

Although upper airway anatomy is clearly an important factor contributing to upper airway collapse in OSA, non-anatomical factors such as compensatory upper airway muscle responsiveness, arousal threshold, and respiratory control stability (or loop gain) may also play a role. It is possible that the relative contributions of these OSA phenotypes may differ between ethnic groups, thereby contributing to the differences in the prevalence and severity of OSA observed between ethnic groups.

Conclusion

The current evidence from a growing number of inter-ethnic population studies suggests that OSA is more prevalent and severe amongst Chinese populations compared with those of European ancestry. Obesity appears to be the strongest contributing risk factor for OSA in all ethnic groups studied thus far, although in Chinese and Japanese populations OSA occurs at a significantly lower BMI. This may reflect a stronger influence of craniofacial restriction on upper airway size in Asians, although

Conflicts of interest

The authors have no conflict of interest to declare.

Funding sources/sponsor

None.

Acknowledgements

None.

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