Metabolic Syndrome (MS) is comprised of a constellation of features consisting of obesity, hypertension (HTN), diabetes mellitus (DM) and dyslipidemia (abnormal cholesterol and triglyceride profiles). There is increasing speculation that both obstructive sleep apnea (OSA) and cardiovascular disease (CVD) may both be mediated by the MS. A recent Mayo clinic study found that MS was more prevalent in patients with OSA (60%) than in patients without OSA (40%). A recent school of thought is that the presence of MS and OSA work together to increase CVD risk since both disorders are predictive of increased cardiovascular morbidity and mortality.
Roughly 2/3 of American adults are either overweight or obese. A recent study of obese men without major medical illnesses found that 60% had sleep disordered breathing (SDB) and 27% had OSA. Estimates of obesity in patients with OSA have ranged from 60-90%. Patients with OSA have been found to have leptin resistance which contributes to weight gain. Leptin is a hormone that regulates weight by controlling appetite and metabolism. OSA treatment with CPAP has been shown to result in normalization of leptin levels, a decrease in leptin resistance and a reduction in obesity.
Along with the rise in obesity, the prevalence of type 2 DM has also increased. Diabetes is associated with a deficiency in insulin production. Both obese and non-obese patients with OSA are insulin resistant. Treatment of OSA with NCPAP has been shown to decrease insulin resistance and improve blood sugar control compared with patients with OSA who are not treated.
The relationship between HTN and OSA is complex. Data suggests that more than 40% of patients with OSA have HTN and more than 30% of patients with HTN also have OSA. Sleep apnea has been shown to be an independent predictor of HTN. HTN on the other hand is a significant predictor of cardiopulmonary deaths in patients with OSA. Numerous studies, including the Sleep Heart Health Study, have shown that the more severe the OSA, the greater the likelihood of having HTN. In addition, treatment of OSA with NCPAP results in a decrease in HTN.
The direct causal relationship between dyslipidemia and OSA is less straightforward. Dyslipidemia is a disorder of fat metabolism, caused by excessively high levels of cholesterol, a well accepted risk factor for coronary artery disease. High triglycerides and low levels of HDL are causative factors in dyslipidemia and both are increased with increasing obesity, which is a common risk factor for both OSA and CVD.
Data from the National Health and Nutrition Examination Survey, the National Cholesterol Education Program, the World Health Organization and the American Association of Clinical endocrinologists have shown an increased prevalence of various components of the MS and CVD in patients with OSA as well as an increase in CVD in patients with OSA. In patients with OSA there is a 27% rate of Obesity, 30% rate of HTN, 9.3% rate of DM and 30% rate of Dyslipidemia. In patients with OSA the risk of heart failure is 40%, stroke 60% and coronary artery disease 30% according to data from the SHHS and the NHLBI.
Evidence has accumulated over the past several years, clearly showing a relationship between OSA, MS and CVD. Numerous studies have shown that NCPAP therapy for OSA improves the individual components of the MS, blood sugar levels and cardiovascular disease. OSA is more common than both asthma and adult onset diabetes. It is estimated that untreated OSA will contribute to 38,000 cardiovascular deaths and 42 million dollars spent on related hospitalizations each year. OSA diagnosis and treatment should be a higher priority target for public health interventions aiming at reducing cardiovascular disease, which remains the leading cause of death in developed nations.
A positive response to 2 or more of these questions should result in your referral to a Board Certified Specialist at an Accredited Sleep Center for diagnosis and treatment of OSA.