Elsevier

Sleep Medicine Reviews

Volume 9, Issue 6, December 2005, Pages 419-436
Sleep Medicine Reviews

Clinical review
Ethnicity and obstructive sleep apnoea

https://doi.org/10.1016/j.smrv.2005.04.005Get rights and content

Summary

There is a scarcity of adult prevalence studies of OSA outside the Caucasian populations of North America, Europe and Australia, and comparisons have been complicated by methodological differences in sleep study settings, respiratory events definition, measured risk factors and clinical outcomes, and the lack of objective parameters for the measurement of ethnicity itself. Comparing studies with the same methodological design and respiratory events definition, recent large-scale prevalence studies from Hong Kong, Korea and India show similar OSA rates to populations of mainly Caucasian composition. OSA is a very complex disorder determined by several phenotypes such as obesity, craniofacial structure and abnormalities in neuromuscular and ventilatory control. Genetics may partially explain some of the ethnic clustering of these phenotypes, modulated by cultural and environmental factors. The exact contribution of these component phenotypes to overall OSA risk will be determined by their varying prevalence and relative risk conferred across ethnic groups. For lesser degrees of obesity, Asians are at risk for a more severe degree of illness compared with Caucasians. Inter-ethnic studies suggests that African–American ethnicity may also be a significant risk factor for OSA. The increased prevalences of OSA among American Indians and Hispanic adults, and increased severity among Pacific Islanders and Maoris, were mainly explained by increased obesity parameters. Most cephalometric studies have largely been conducted without specific regard to ethnicity and comparisons of findings across studies have been mainly limited by differences in sampling methods and the varying selection and definition of measured cephalometric variables. The limited number of studies with inter-ethnic comparative data suggest cephalometric variables and their degree of contribution to OSA vary across ethnic groups.

Introduction

Obstructive sleep apnoea (OSA) is a disorder characterized by repetitive episodes of complete or partial upper airway obstruction during sleep, often associated with hypoxemia, increased breathing effort and arousals. OSA has a range of deleterious consequences that include unrefreshing sleep and excessive daytime sleepiness, neurocognitive impairment, and cardiovascular morbidity.1, 2, 3, 4, 5, 6, 7 OSA has been increasingly recognized over many years as an important health issue with major clinical and public health implications.8, 9 The clinical syndrome is typically referred to as OSAS (OSA plus daytime sleepiness) or more recently modified to OSAHS, where H introduces hypopnoea into the acronym.10

The most commonly quoted estimate of prevalence of OSAS derives from a study of middle-aged public servants from Wisconsin, USA: 4% in males, 2% in females.11 The ethnicity of the Wisconsin Sleep Cohort was overwhelmingly Caucasian. This prevalence gives an indication of the minimal size of the health problem associated with sleep apnoea. Documented risk factors for OSA include increasing age, male gender, obesity, craniofacial structure, ventilatory control dysfunction, and there is also some evidence for other risk factors including alcohol and other drugs, and both active and passive smoking. Ethnicity is also suggested as an important associated indicator of OSA risk and/or severity.12, 13, 14, 15, 16 The major purpose of this review will be to consider the ethnic aspects of obstructive sleep apnoea.

Section snippets

Ethnicity and health

The definition of ethnicity or of an ethnic group in medical literature is not always clear, but would generally pertain to a group of individuals sharing a common racial and/or cultural background.17 A very broad connotation of race separates just three categories, i.e. African, Caucasian and Mongoloid (sic), but this limited classification can be criticised on numerous grounds. Mixing of the human genetic pool has long occurred in developed countries, and in previously colonized regions of

Adult prevalence

Previously published reviews of OSA epidemiology have largely described prevalences from studies in predominantly Caucasian populations. A 1996 review20 included 12 prevalence studies, which varied considerably in the methods used, particularly systematic use or not of polysomnography (PSG) as the arbiter of OSA, the definitional criteria for OSA, geographical location and gender inclusiveness. Estimated whole population prevalences varied between 0.3 and 15%, although the authors went on to

Ethnicity as an OSA risk factor

Genetics, culture, environment (incorporating socioeconomic status) and development may all influence separately or in various combinations some of the recognized OSA risk factors. In addition, these components to a greater or lesser degree inform the construct of ethnicity which itself has been identified as a separate OSA risk factor. This complex amalgam of influences makes analysis of the contribution of ethnicity to OSA problematic (Fig. 1).

Craniofacial structure and upper airway

Craniofacial structure has both a bony component and a soft tissue component. The former would be expressed in adults in the relatively fixed elements of the skull, facial bones and cervical spinal skeleton, which in concert provide the bony framework and support of the upper airway. Those fixed elements can be identified on lateral cephalograms and are usually expressed as indicative angles and linear distances, and two-dimensional areas. It is then possible to establish norms for those bony

Phenotypic interactions

The racial variations in the prevalence and expression of these phenotypes may be related to ethnic differences in risks for obesity, craniofacial morphology and ventilatory control. Directly, these factors which are to some extent heritable, in various combinations and modulated by cultural and environmental influence, will determine the overall susceptibility for collapse of the upper airways.69 The interaction of these factors with each other may also serve to modify the contribution

Acknowledgements

The authors are grateful for the assistance provided by Dr Louis Wong during the initial draft of the paper. We would also like to thank Maria Vanessa V Alvarez for her invaluable help in the creation of the graphics used for the cephalometric figures.

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