, according to results of a study published in Nature and Science of Sleep (2021:13 1771-82).
Layla B. Guscoth, MD, of the South Australian Health and Medical Research Institute and Faculty of Health and Medical Sciences, University of Adelaide, Australia, and colleagues assessed unselected male community-dwelling participants in the Men Androgen Inflammation Lifestyle Environment and Stress (MAILES) and the Florey Adelaide Male Aging Study (FAMAS) studies.
They examined the association of OSA and nocturnal hypoxemia with serum lipid profiles, and suggested that the cardiometabolic risk profiles of healthy weight individuals with OSA require clinical attention, according to the researchers.
The partial or complete obstruction of upper airways found in the OSA syndrome results in intermittent hypoxia, accompanied variably by sleep fragmentation and daytime sleepiness. While the prevalence of moderate to severe OSA was 49.7% in the Swiss HypnoLaus cohort, it was 74.7% in men aged 40 or older (or having OSA syndrome according to ICD-3 criteria). Dr. Guscoth and colleagues point out, however, that OSA is frequently underdiagnosed or unrecognized in clinical settings, and that OSA has been implicated in development of cardiovascular conditions. Furthermore, the nocturnal hypoxemia resulting from OSA during rapid eye movement (REM) sleep is longitudinally associated with cardiovascular disease and its risk factors (hypertension, insulin resistance, metabolic syndrome and carotid atherosclerosis).
Study details
Prior research suggests that intermittent hypoxemia activates the sympathetic nervous system, increases oxidative stress and systemic inflammation, and that when chronic, reduces clearance of triglyceride-rich lipoproteins and inhibits adipose tissue lipoprotein lipase activity. To clarify inconsistent results in studies investigating potential OSA-dyslipidemia associations, and to confirm research suggesting an independent association with severe OSA (apnea-hypopnea index [AHI] ≥ 30/h), the authors conducted analyses stratified by waist circumference to observe an obesity-independent association between OSA metrics and dyslipidemia.
The investigators assessed 753 MAILES participants (mean age 60.8 years) who underwent full in-home polysomnography (Embletta X100). They looked at triglycerides, high- (HDL) and low-density lipoprotein (LDL), total cholesterol, associations between lipids and continuous measures of nocturnal hypoxemia (oxygen desaturation index [ODI], AHI, and REM-AHI), and adjusted for chronic conditions, risk behavior, and sociodemographic factors.
Mean waist circumference was 99.3 cm and OSA (AHI ≥ 10) prevalence was 52.6%. No significant associations were found between OSA metrics and lipid measures in an overall analysis, nor in a sensitivity analysis excluding lipid-lowering therapies.
In a covariate adjusted analysis stratified according to waist circumference (< 95 cm, 95-100 cm, > 100 cm) to minimize the contribution of obesity to hypertriglyceridemia, triglyceride levels were positively associated with AHI, ODI and REM-AHI in the participants with a waist circumference < 95 cm (P < .05), but not in participants with waist circumferences of 95-100 cm or > 100 cm.
Worse during REM
The authors observed also that OSA during REM sleep is marked by longer obstructive events with greater oxygen desaturations. Obstructive events during REM sleep, research has shown, may be more harmful than obstructive events during non-REM sleep with respect to hypertension, cardiovascular disease, and glycemic control in type 2 diabetes.
Looking at clinical categories of OSA, Dr. Guscoth and colleagues found that severe OSA was significantly associated with higher likelihood of triglyceride levels ≥ 1.7 mmol/L (odds ratio, 4.1, 95% confidence interval, 1.1-15.5, P = .039). Analysis according to waist circumference confirmed the relationship only among men with waist circumference < 95 cm.
Clinical concern
“We therefore suggest that with our data unstratified by weight circumference, metabolic derangements associated with insulin resistance induced by intermittent hypoxia due to OSA cannot be separated from the predominant effect of visceral obesity. When stratified by weight circumference, our data show that these derangements in triglycerides are observed only in lean participants where obesity does not have a dominant effect,” the researchers concluded.
“These findings of high prevalence of metabolic risk in lean patients with OSA, I find very worrying,” coauthor Sarah Appleton, PhD, Flinders Medical Center, Adelaide, Australia, said in an interview. She cited a study showing a 61% risk of dyslipidemia in lean patients with OSA (AHI > 5/hr, body mass index < 25 kg/m2, and waist < 80 cm in women, < 90 cm in men), and two of three metabolic syndrome components in 64%. “Annual fasting blood tests would identify metabolic problems such as elevated fasting glucose and triglyceride levels,” she noted.
This work was supported by a National Health and Medical Research Council of Australia Project Grant (627227), the Hospital Research Foundation and ResMed Foundation. There were no relevant conflicts reported.