Original ArticleObstructive Sleep Apnea Syndrome in the Sao Paulo Epidemiologic Sleep Study
Introduction
Obstructive Sleep Apnea Syndrome (OSAS) is a significant public health problem associated with hypersomnolence, accidents, cardiovascular morbidity, cognitive impairment, anxiety, depression, and metabolic dysfunction [1], [2], [3], [4], [5].
OSAS can be influenced by both genetics and the environment, and it is important to determine the prevalence of OSAS in specific populations. Although OSAS has been studied in North America, Europe, Asia, Australia, and India, no comprehensive studies have been conducted in South America [6], [7], [8], [9], [10], [11], [12], [13], [14].
Earlier studies estimated that between 3.7% and 26% of the population has an Apnea-Hypopnea Index (AHI) above 5. The prevalence of OSAS, defined by AHI frequency and the presence of hypersomnolence, has been estimated to range from 1.2% to 7.5% [6], [7], [8], [9], [10], [11], [12], [13], [14]. These wide variations are partly the result of the lack of homogeneity in epidemiologic studies. Some studies, for example, were performed in pre-selected population groups (e.g., state agency employees, industrial employees, or clinically referred patients) and included a high number of subjects who were suspected of having OSAS because of their snoring frequency [15]. Moreover, some earlier studies did not include subjects over 60 years of age [6], [9], [10], [11], [12], [13], [14]. Many studies were conducted before the development of the nasal cannula and used a thermistor to record airflow during sleep, which is a less sensitive device to detect abnormal sleep respiratory events. Finally, earlier investigations did not use the most recent criteria for OSAS diagnosis from the International Classification of Sleep Disorders (ICSD-2, 2005) of the American Academy of Sleep Medicine (AASM) [16]. Previously, significant daytime sleepiness and strictly scored apneas and hypopneas (AHI > 5) were required to establish the final clinical diagnosis of OSAS. The definition of OSAS has been changed with the introduction of ICSD-2, including symptoms besides daytime sleepiness in association with an AHI between 5 and 15 or an AHI equal to or higher than 15 obstructive events per hour of sleep regardless of the presence of any complaints.
The aim of the present study, which used current clinical and epidemiologic techniques and procedures, was to estimate the prevalence of OSAS according to age, gender, socio-economic status, and Body Mass Index (BMI) in a probabilistic sample representative of the adult population of Sao Paulo, Brazil.
Section snippets
The population under investigation
Sao Paulo, Brazil is the largest city in the southern hemisphere [17] and had a population of 10,886,518 in January 2008. Studies of genetic markers indicating ancestry have found that there are high levels of ethnic admixture in this population [18].
The protocol for this study was approved by the Ethics Committee for Research of the Universidade Federal de Sao Paulo (CEP 0593/06) and was registered with ClinicalTrials.gov (number NCT00596713). Selected volunteers read and signed an informed
Results
The distributions of gender, age, socio-economic status, and BMI among the sample of Sao Paulo residents (n = 1042) were similar to the demographic projections of the 2000 census (Table 1). Women constituted 55% of the study population, 75% of the population participated in the work force, and 59.9% of the subjects were overweight or obese (BMI > 25 kg/m2).
Weighted prevalence estimates of OSAS symptoms show that 55% of the population experiences sleepiness, 38.9% fatigue, 20.5% report snoring, and
Discussion
This is the first population-based survey of OSAS prevalence carried out in a probabilistic sample representative of a large metropolitan area. The study used comprehensive techniques and procedures and had a very low participant refusal rate (5.4%). The refusal group did not differ significantly from the final sample group in regard to age, gender, socio-economic status, or subjective sleep quality [19]; the prevalence estimates can therefore be assumed to be free from selection bias. In
Acknowledgments
This work was supported by grants from the Associaçao Fundo de Incentivo a Psicofarmacologia (AFIP) and FAPESP (#07/50525-1 to RS-S, and CEPID no. 98/14303-3 to ST). ST, LRAB and JAT received the CNPq fellowship. The authors would like to thank Fernando Colugnati for valuable suggestions and statistical analyses. All the efforts of AFIP’s staff, in particular those of Roberta Siuffi, are deeply appreciated.
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