Is sleep-disordered breathing an independent risk factor for hypertension in the general population (13,057 subjects)?

Abstract

Objective: Sleep-disordered breathing has been hypothesized to have a close relationship with hypertension but previous studies have reported mixed results. This is an important health issue that requires further clarification because of the potential impact on the prevention and control of hypertension.Methods: The relationship between hypertension and three forms of sleep-disordered breathing (chronic snoring, breathing pauses and obstructive sleep apnea syndrome (OSAS)) was assessed using representative samples of the non-institutionalized population of the UK, Germany and Italy (159 million inhabitants). The samples were comprised of 13,057 individuals aged 15–100 years who were interviewed about their sleeping habits and their sleep symptoms over the telephone using the Sleep-EVAL system.Results: OSAS was found in 1.9% (95% CI: 1.2% to 2.3%) of the UK sample, 1.8% (95% CI: 1.4% to 2.2%) of the German sample and 1.1% (95% CI: 0.8% to 1.4%) of the Italian sample. OSAS was an independent risk factor (odds ratio (OR): 9.7) for hypertension after controlling for possible confounding effects of age, gender, obesity, smoking, alcohol consumption, life stress, and, heart and renal disease.Conclusions: Results from three of the most populated countries in Western Europe indicate that OSAS is an independent risk factor for hypertension. Snoring and breathing pauses during sleep appeared to be non-significant predictive factors.

Introduction

The relationship between sleep-disordered breathing and hypertension is a major issue requiring elucidation, especially as appropriate treatment of the former may help control or even protect against the latter. However, the literature review on this topic raises many ambiguities.

(1) A major source of ambiguity lies in the terminology used by the authors. There is some confusion between obstructive sleep apnea (OSA), a polysomnographic entity associated with several pathologies, and obstructive sleep apnea syndrome (OSAS), a specific clinical entity associated with a polysomnographic pattern (apnea/hypopnea index (AHI) >five apneas plus hypopneas per hour of sleep) and characterized by daytime sleepiness or insomnia but dissociated from obesity. This conceptual misunderstanding has prevailed since the 1970s [1], [2], [3], [4]. Recent reviews [5], [6] regarding the association between hypertension and sleep-disordered breathing failed to make the distinction between OSAS and multi-morbid syndromes associating obesity and OSA. Therefore, the relationship between OSAS and hypertension remains poorly defined.

(2) In addition to this problem of terminology, general population studies of hypertension and sleep-disordered breathing are rare. Gislason et al. [7] explored this association in a representative sample of the Swedish male population. Although other studies may involve large samples, as was the case with the Wisconsin sleep cohort [8] and the Busselton cohort in Australia [9], findings were applied to the general population only through secondary extrapolation which may or may not be valid depending on the initial population.

(3) Finally, the identification of confounding variables may impact the association between sleep-disordered breathing and hypertension. Obesity, smoking and alcohol consumption are not always considered and are often inadequately assessed [10]. Moreover, life stress, which may be equally important, has not been included in any study to date.

Consequently, we decided to assess the relationship between hypertension and three forms of sleep-disordered breathing: namely, chronic snoring, breathing pauses and OSAS, in the course of telephone surveys undertaken in the general populations of the UK, Germany and Italy. This report presents the results obtained after controlling for confounding variables: age, body mass index (BMI), alcohol, smoking, life stress and heart and renal diseases.