Nonobese Sleep Apnea Patients May Be At Risk for Factors of Metabolic Syndrome

Key Point

Patients with obstructive sleep apnea who are not obese may be at risk for dyslipidemia, hypertension, and hyperglycemia.

Obstructive sleep apnea syndrome (OSAS) may be associated with several factors that define metabolic syndrome, regardless of the presence of visceral fat accumulation, according to results published in the May Chest. Masakazu Kono, MD, and colleagues found that dyslipidemia, hypertension, and hyperglycemia were linked to OSAS independently of obesity, which raises the possibility that even OSAS patients who are not obese may be at risk for metabolic syndrome.

Dr. Kono, of the Department of Respirology at the Graduate School of Medicine at Chiba University in Japan, and colleagues examined 42 men with OSAS and 52 men without OSAS who were matched for age, BMI, and visceral fat accumulation. There were no significant differences between groups with regard to serum levels of triglycerides or HDL cholesterol, or in diastolic blood pressure, although fasting blood glucose measured 111 mg/dL among patients with OSAS and 93 mg/dL among those without OSAS.

Dyslipidemia, hypertension, and hyperglycemia were diagnosed in 48%, 45%, and 33% of patients in the OSAS group, respectively, compared with 25%, 15%, and 10% in the group without OSAS. Furthermore, 19% of patients with OSAS had at least two of the three preceding diagnoses, compared with 4% of patients without OSAS. Dr. Koto’s team stated, “Logistic regression analyses showed that [apnea-hypopnea index] value was the predictor of the number of metabolic syndrome param­eters ... while BMI and lowest [arterial oxygen saturation] during sleep [were] not.”

The authors discussed several possible mechanisms underlying the correlation between OSAS and metabolic syndrome. Disorders of lipid metabolism such as dyslipid­emia play a role in atherosclerotic vascular wall changes, and increased sympathetic activation, leptin, aldosterone, fatty acids and oxidative stress could allow OSAS to contribute to hypertension in obese individuals. Although factors other than obesity can lead to hypertension, insulin resistance can also predispose patients with OSAS to develop hypertension.

Insulin resistance itself plays a significant role in the pathogenesis of metabolic syndrome and may be associated with OSAS; obesity and visceral fat accumulation both increase insulin resistance and are OSAS risk factors. “[Visceral fat accumulation] increases the risk for obesity-related disorders such as vascular-related diseases,” while “[o]besity, especially the presence of [visceral fat accumulation], could worsen metabolic abnormalities such as insulin resistance [which is] a putative background of the metabolic syndrome,” Dr. Kono and colleagues noted. “Since continuous positive airway pressure treatment improves insulin sensitivity in patients with OSAS within a few days before any possible changes in body weight or lifestyle, OSAS itself appears to predispose to insulin resistance.”

Furthermore, while “intermittent hypoxia is likely to aggravate the insulin resistance associated with significant [visceral fat accumulation] in patients with OSAS,” the researchers stated, intermittent hypoxia may not be severe enough to affect lipid metabolism. The researchers suggested that an interventional study using continuous positive airway pressure could determine whether OSAS and metabolic syndrome share a common “patho­mechanism” besides visceral obesity.

“If OSAS was a risk factor for metabolic syndrome, any factor related to the pathophysiology of OSAS, such as intermittent hypoxia, increased oxygen-radical production, and membrane lipid peroxidation, would contribute to the development of metabolic syndrome,” Dr. Kono’s team pointed out. “Early intervention may help to decrease the cardiovascular morbidity and mortality associated with OSAS and metabolic syndrome.”            

—John Merriman

Reference
Kono M, Tatsumi K, Saibara T, et al. Obstructive sleep apnea syndrome is associated with some components of metabolic syndrome. Chest. 2007;131:1387-1392.

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