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WESTCHESTER, Ill. – A study in the July 1 issue of the journal Sleep shows that episodes of sleep-disordered breathing accompanied by mild oxygen desaturations of as little as two percent are associated with hyperglycemia.
Adults with 11 or more apnea-hypopnea events per hour with an oxygen desaturation of 2.0 percent to 2.9 percent had an adjusted cumulative odds ratio of 1.41 for impaired fasting glucose or diabetes. Apneas are complete pauses in breathing, and hypopneas are partial reductions in breathing. Events must last at least 10 seconds to be considered an episode of sleep-disordered breathing.
Because of a low occurrence of apneas in the study group, results also were calculated for hypopneas alone. Adults with 10 or more hypopnea events per hour that were accompanied by an oxygen desaturation of 2.0 percent to 2.9 percent had a similar odds ratio of 1.44.
“We did not expect to find that subtle decreases in oxygen levels would independently correlate with fasting hyperglycemia – a marker of insulin resistance and future diabetes risk,” said senior author Dr. Naresh Punjabi, associate professor of medicine and epidemiology at Johns Hopkins University in Baltimore, Md. “Perhaps the most surprising part was that the association remained even after we accounted for more severe drops in oxygen levels during sleep.”
The study group involved 2,656 participants in the ongoing Sleep Heart Health Study. Their average age was 68 years. Sleep was measured by unattended polysomnography in the participants’ homes. Within one year of a participant’s polysomnogram, a blood sample was taken after 12 or more hours of overnight fasting. Glycemic status was categorized as normal, impaired or diabetic. The overall prevalence of diabetic glucose values was 5.8 percent.
Previous studies have shown a link between sleep-disordered breathing and the prevalence of altered glucose metabolism and type 2 diabetes. According to current recommendations in the field of sleep medicine, however, hypopneas are counted during polysomnography only if they are accompanied by an oxyhemoglobin desaturation of at least three or four percent.
The study describes multiple mechanisms by which sleep-disordered breathing (SDB) may impair glucose metabolism. These include the repetitive cycles of hypoxemia and re-oxygenation, the related sleep fragmentation, and the resulting release of hormones such as cortisol.
“If future studies continue to support a causal role of SDB in mediating excess metabolic risk, the implications of our study are that even milder forms of SDB are clinically relevant,” said Punjabi.
Obstructive sleep apnea (OSA) is a common form of sleep-disordered breathing that involves a decrease or complete halt in airflow despite an ongoing effort to breathe. It occurs when the muscles relax during sleep, causing soft tissue in the back of the throat to collapse and block the upper airway.
Information for patients and the public is available from the American Academy of Sleep Medicine about sleep and diabetes at http://www.sleepeducation.com/Article.aspx?id=649 and about OSA at http://www.sleepeducation.com/Disorder.aspx?id=7.
Sleep is the official journal of the Associated Professional Sleep Societies, LLC, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society.
For a copy of the study, “Fasting Glycemia in Sleep Disordered Breathing: Lowering the Threshold on Oxyhemoglobin Desaturation,” or to arrange an interview with an AASM spokesperson, please contact Kathleen McCann, AASM director of communications, at (708) 492-0930, ext. 9316, or email@example.com.