Elsevier

Sleep Medicine Reviews

Volume 17, Issue 5, October 2013, Pages 321-329
Sleep Medicine Reviews

Clinical review
Obesity and obstructive sleep apnea – Clinical significance of weight loss

https://doi.org/10.1016/j.smrv.2012.08.002Get rights and content

Summary

Obesity is a major health burden that contributes to increased morbidity and mortality. Obesity is also the most important risk factor for obstructive sleep apnea (OSA); at least 70% of patients are obese. OSA as such, has been linked with increased cardiovascular morbidity and mortality, and OSA patients often display metabolic syndrome. The exact underlying mechanisms behind these associations are complex and not fully understood. In obese individuals, weight reduction and increased physical activity form cornerstones for the prevention and treatment of metabolic syndrome, and recent controlled intervention trials strongly suggest that weight reduction together with a healthy diet and increased physical activity may correct or at least improve the symptoms of OSA. However, regardless of promising results in terms of symptoms of OSA and the undoubted metabolic benefits of changing lifestyles, weight reduction as a treatment of OSA is still underrated by many clinicians. Based on the current knowledge, clinicians should revise their previous attitudes, including suspicions about weight reduction as an effective treatment for OSA patients. Nevertheless, we also need large well-controlled trials on the effects of different weight reduction programs among OSA patients to determine the overall efficacy of different treatment modalities and their long-term success.

Introduction

Obesity has become a serious health concern in recent decades, leading to increased morbidity and mortality, in particular from cardiovascular diseases.1, 2 Obesity is also the most important risk factor for obstructive sleep apnea (OSA) and in fact, most OSA patients (at least two out of every three) are obese.*3, 4, *5 The co-existence of obesity and OSA has a complex and far more serious impact on the cardiovascular and metabolic sequelae than either of these conditions on their own. OSA as such, has been found to have an independent association with cardiovascular diseases, type 2 diabetes, metabolic syndrome, deterioration of an individual’s quality of life and working capacity, and increased mortality.*5, 6, 7, 8, 9, 10, 11, 12 The importance and the effectiveness of weight loss in treating OSA have been well-known for more than two decades. The majority of the earlier studies on weight reduction in OSA patients evaluated either the effects of low and very low calorie diet programs in moderately overweight patients or the effects of bariatric surgery upon weight and concurrent OSA in severely obese patients.13, 14, 15, 16, 17, 18, 19 These studies have lead to conclusions that weight loss could reduce the severity of OSA, but that it was not a curative treatment for most patients. However, although weight reduction is recommended in all clinical guidelines, until recently there has been a lack of well-executed randomized intervention studies on the effect of weight reduction upon OSA.20 In the first randomized study to be conducted, we demonstrated that a lifestyle intervention lasting one year including an early weight reduction program represented a feasible and curative treatment for the vast majority of overweight patients with mild OSA.21 These findings have been supported by two other recent randomized studies, one examining obese OSA patients with type 2 diabetes and the other in obese patients with severe OSA, including an observational follow-up phase.*22, *23, *24 Most importantly, although the results of these and earlier studies are encouraging, it is not known, whether these favorable changes can be sustained after the discontinuation of the intervention. The recent post-interventional follow-up of our randomized study demonstrated that a successful weight reduction with lifestyle intervention can maintain the improvements of OSA for at least one year after the actual termination of the intervention.25 In earlier reviews on OSA, virtually no attention has been paid to the weight reduction as a potential key treatment modality not only for OSA but also for related co-morbidities. Recently this topic has finally attracted attention because of well-designed intervention trials, which unequivocally highlight the potential of weight reduction in this condition. It should be noted that weight reduction, more physical activity and adopting a healthy diet may have a marked influence on the well-being and cardiovascular risk of the OSA patients due to their beneficial effects on many cardiovascular and metabolic risk factors, e.g., glucose metabolism.3 The aim of this review is to focus on the new information on the importance of weight loss in the treatment of OSA and its metabolic co-morbidities in overweight patients.

Section snippets

Epidemiology of obesity and OSA

Excess body weight is perhaps the greatest health burden throughout the world, affecting almost every aspect of life and representing a major challenge to medical practice. It has been estimated that globally 1.6 billion adults are overweight [body mass index (BMI) > 25 kg/m2] and 400 million are obese (BMI >30 kg/m2).26 In the U.S.A., one out of every three adults has categorized as being obese.27 In Europe, the trends are in the same direction, for example in Finland one out of every five adults

Pathophysiology and risk factors of OSA

OSA occurs when there are repetitive collapses of the upper airway during sleep causing an obstruction of breathing, reduction in airflow and oxygenation. For patients with OSA, these disturbed nocturnal breathing functions also result in recurrent arousals causing a significant fragmentation of their sleep. The pathophysiology of OSA is complex and most likely multifactorial, consisting of a combination of predisposing anatomical factors and impaired neuromuscular compensatory responses.

Clinical symptoms related to OSA

The recurrent upper airway obstruction and the resulting interruptions in breathing during sleep characterized by OSA, are manifested as loud snoring, pauses in breathing, and sleep fragmentation. Due to the sleep fragmentation, OSA is often accompanied by daytime symptoms; fatigue, lack of concentration, morning headache, impotence, deterioration of an individual’s quality of life and working capacity.8, 11, 31 The breathing pauses can be divided into apneas and hypopneas; there is a total

Obesity related pathophysiology of OSA

The association between obesity and OSA seems to be bi-directional; obesity itself increases the risk for OSA, but, on the other hand, OSA may also predispose the individual to weight gain*3, *5, *33 (Fig. 1). There is current evidence that systemic inflammatory mediators related to obesity and localization of excess adipose tissue, e.g., increased fat tissue in the neck may have additional effects also in pharyngeal neural and mechanical control mechanisms that mediate collapsibility and

Weight reduction in OSA

The importance and the effectiveness of weight loss in treating OSA have been recognized for more than 25 years.15 The majority of the weight reduction and OSA studies have evaluated either the effects of low and very low calorie diet (VLCD) programs in moderately overweight patients with OSA or the effects of bariatric surgery upon weight and concurrent OSA in severely obese patients.13, 14, 15, 16, 17, 18, 19 Overall, the average weight loss and improvement in AHI after dietary interventions

Metabolic syndrome and OSA

Metabolic syndrome is a cluster of risk factors, which alone or in different combinations increase the risk for type 2 diabetes, cardiovascular morbidity and mortality.64 A recent study also suggested that sleep disturbance co-aggregated with other components of the metabolic syndrome and could be the second most important determinant after obesity.65 There are several reports that OSA is also associated with the metabolic syndrome and type 2 diabetes.7, 10, 31, *33, 65, 66, 67 In clinical

Cardiovascular consequences of obesity and OSA

OSA has been frequently been linked with cardiovascular diseases. The exact underlying mechanisms explaining the association between cardiovascular morbidity and OSA are not fully understood, although a multifactorial etiology is most likely.71, 72 Even mild OSA is associated with increased activation of the inflammatory system and a risk for cardiovascular morbidity, although the risk is more frequently associated with more severe degrees of the disease.73, 74 On the other hand, what was

Importance of weight loss – comeback of an abandoned cure

The improvement of OSA is highly associated with weight loss, and treatment results are comparable to those achieved by weight reduction in other obesity related morbidities. Table 3 summarizes the large body of evidence favoring lifestyle modification in the prevention and treatment of all obese related conditions. Weight reduction has been shown to result in a marked improvement in insulin resistance, and in some studies in type 2 diabetics also recovery of normal insulin secretion has been

Conclusion

Based on the current knowledge, weight reduction is a very effective treatment modality in overweight patients with OSA, and therefore, it should always be included in the treatment of OSA when this is linked to excess weight. In addition to improving OSA, weight reduction also improves the other obesity related disturbances of metabolic syndrome, e.g., the increased risk for cardiovascular diseases and type 2 diabetes. The cornerstone of treatment of overweight patients must be weight

Conflict of interest statement

We declare that we have no conflicts of interest.

Acknowledgments

Juho Vainio Foundation, Paavo Nurmi Foundation, Finnish Anti-Tuberculosis Foundation and the Research Foundation of the Pulmonary Diseases have supported the work with grants. The funding sources had no role in interpretation of the literature or writing of the report. The authors had final responsibility to submit the report for publication.

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