Many people snore. Many people have heart attacks. Researchers from the University of Pittsburgh say they have found a connection between the two conditions. “People often report in primary care offices that they or their spouse complains of loud snoring, that they have difficulty falling asleep or staying asleep. And we as sleep researchers were interested in how this broad array of sleep symptoms that are often reported might relate to later cardiovascular risk,” lead research author Wendy Troxel of the University of Pittsburgh School of Medicine said.
Previous research has looked at the link between heart disease and obstructive sleep apnea, a problem where excess tissue blocks the airway during sleep. But this study looked purely at snoring. “There are some people with loud snoring who don't have obstructive sleep apnea,” Troxel continued.
In Troxel's government-funded study, more that 800 relatively healthy people ages 45 to 78 were followed for three years. High blood sugar and low levels of good cholesterol, both risk factors for heart disease, were twice as likely to present in the participants who reported frequent, loud snoring.
In addition to snorers, participants who had trouble falling asleep and had unrefreshing sleep were also at increased risk for metabolic syndrome, when additional heart disease risk factors like obesity, high blood pressure, and high levels of triglyceride fats are present. “Sleep complaints aren't just benign annoyances but something that can really foretell important health consequences,” Troxel stressed, “and they should really be discussed with [medical] providers and referred for further treatment if necessary.”
The research conducted at Pitt was an observational study. Patients were not treated to see whether decreasing snoring could lower the risk of heart disease. Rather, the study shows that snorers should pay particular attention to their heart disease risk factors.
To determine whether intermittent hypoxia (IH) and chronic hypoxia (CH) would have different metabolic effects, Dr. Lee and colleagues fitted adult male mice with arterial and venous catheters for continuous rapid blood monitoring of glucose and insulin sensitivity.
They then exposed the mice to either seven hours of IH, in which treatment, oxygen levels oscillated, reaching a low of about 5 percent once a minute, or CH, in which they were exposed to oxygen at a constant rate of 10 percent, and compared each treatment group to protocol-matched controls.
When compared to the control group, the IH mice demonstrated impaired glucose tolerance and reduced insulin sensitivity; the CH group, however, showed only a reduction in glucose tolerance but not insulin sensitivity compared to controls. “Both intermittent hypoxia and continuous hypoxia exposed mice exhibited impaired glucose tolerance, but only the intermittent hypoxia exposed animals demonstrated a reduction in insulin sensitivity,” said Euhan John Lee, M.D., a fellow at the Medical Center.
“The intermittent hypoxia of sleep apnea and the continuous hypoxia of altitude are conditions of hypoxic stress that are known to modulate glucose and insulin homeostasis. Although both forms of hypoxia worsen glucose tolerance, this research demonstrated that the increase in insulin resistance that accompanies intermittent hypoxia, or sleep apnea, is greater than that seen with continuous hypoxia, or altitude,” explained Dr. Lee.
The specific finding that intermittent, but not continuous, hypoxia induced insulin resistance was not expected.
Increased generation of reactive oxygen species, initiation of pro-inflammatory pathways, elevated sympathetic activity, or upregulation of insulin counter-regulatory hormones in IH may contribute to the greater development of insulin resistance in those mice versus those exposed to continuous hypoxia.
“As sleep apnea continues to rise with the rate of obesity, it will be increasingly important to understand both the independent and interactive effects of both morbidities on the development of metabolic disorders. This research demonstrated that intermittent hypoxic exposure can cause changes in insulin sensitivity and insulin secretion, which may have important consequences in metabolically vulnerable diabetic patients who present with co-morbid sleep apnea,” said Dr. Lee. (ANI)