Sleep Apnea Reduces Good Cholesterol Levels
The more severe the apnea, the lower the level of good cholesterol in the blood, according to researchers from Bochum in Germany. Their study, to be published in January's issue of the European Respiratory Journal, also shows that treating sleep apnea improves patients' lipid profile and reduces cardiovascular risk.
It has been recognized for several years that obstructive sleep apnea syndrome (interruptions to breathing for over 10 seconds, five times per hour or more) is associated with several cardiovascular risk factors, including a significant rise in blood pressure.
Apnea's damaging input in cardiovascular disease could also affect lipid metabolism, in other words the levels of "good" and "bad" cholesterol, which are involved, for example, in myocardial infarction.
This was what Jan Brgel and his team, of Bochum in Germany, set out to examine through their prospective study on the role of apnea and its treatment on serum lipid levels.
The study, published in the European Respiratory Journal (ERJ), covers 470 patients who sought treatment for sleep problems at the Marienhospital Herne, a hospital of the Ruhr-University Bochum, and were diagnosed with apnea via polysomnography. It paves the way for significant breakthroughs in primary and secondary prevention of cardiovascular events.
The more serious the apnea, the lower the level of good cholesterol
Through analysis of the lipid profile of the 470 patients, whose average apnea/hypopnoea index was 28 episodes per hour, the researchers discovered, first of all, that triglyceride levels rose in proportion to the severity of the apnea, while "good" cholesterol levels fell. "Good" cholesterol, also known as high-density lipoprotein or HDL cholesterol, is believed to reduce fatty deposits within arteries, which are, conversely, increased by "bad" cholesterol (low-density lipoprotein or LDL cholesterol).
Thus, for a low apnea index of between 11 and 21 per hour, the good cholesterol level was found to average 50mg/dl and the triglyceride level 150mg/dl. Yet in patients with an apnea index of between 42 and 102, the good cholesterol level fell to 40 mg/dl while the triglyceride level rose to 175mg/dl.
It should be noted, however, that only the connection between degree of apnea and "good" cholesterol is statistically independent of other variables, namely age, sex, body mass index, diabetes or lipid lowering medication. "What's particularly important is that this link does not depend on obesity, a co-morbidity frequently found in such patients, which could have been a confounding factor," Brgel emphasises. "The mechanism could be hyperactivity of the sympathetic nervous system, but that is only a hypothesis for now," he adds.
Apnea treatment increases good cholesterol
There is proof that apnea is truly associated with the reduction in "good" cholesterol: the standard treatment used to control obstructive sleep apnea syndrome has a remarkable effect, according to the ERJ article. (This well-known treatment consists of blowing air into the patient's airways to stop them collapsing, and is hence known as Continuous Positive Airway Pressure, or CPAP).
For a sub-group of 127 patients who underwent six months of CPAP, the average level of good cholesterol rose from 46.9mg/dl to 49.6mg/dl, a rise of 5.8%. In parallel, there was a fall in levels of triglycerides (-8.6mg/dl), "bad" cholesterol (-5.5mg/dl) and total cholesterol (-3.4mg/dl), but not at a statistically significant level.
"The treatment benefited all of the patients who presented lipid disorders at the start of the study," emphasise the authors. "Continuous positive airway pressure may work by reducing the activity of the sympathetic nervous system. But it may also be the case that it has a much less direct effect on the level of good cholesterol, for example by reducing the daytime sleepiness associated with apnea and thus encouraging the resumption of physical activity." Brgel and his colleagues hope shortly to explore this hypothesis.
Preventing cardiovascular disease
The results published in January's ERJ should allow a better understanding of the relatively high incidence of cardiovascular disease found in patients with obstructive sleep apnea. They also emphasise the decisive role of continuous positive airway pressure therapy.
This opens up exciting new horizons, and randomised studies should provide more precise details of the relationship linking obstructive sleep apnea and HDL cholesterol levels. So practical recommendations may be just around the corner.
Title of the original article: Obstructive sleep apnea and its therapy influence high-density lipoprotein cholesterol serum levels.
By European Respiratory Journal
This page is updated on May 11, 2013.