An article in the December issue of the Sleep Journal has received media attention, so I thought I would summarize it here.
Metabolic syndrome is defined as having three or more of the following: elevated blood glucose, increased waist circumference, high blood pressure, increased triglycerides, and low HDL (the good cholesterol). It is estimated that 20% of us have the metabolic syndrome.
The authors of this study assessed over 800 people ages 45 to 74 over a three year period to see if they developed the metabolic syndrome and if it was associated with any sleep symptoms. They used a subjective questionnaire to assess insomnia symptoms, loud snoring, gasping at night, and/or nighttime choking. Sleep duration was not assessed. Almost 300 of the study participants volunteered to have a home sleep study (Resmed's ApneaLink) at the end of the three years.
Over the three year span of time, 14% developed the metabolic syndrome. The sleep symptoms that were statistically related to metabolic syndrome were difficulty falling asleep, unrefreshing sleep, loud snoring, and elevated score on the ApneaLink home sleep study. There was no interaction with race of gender. Loud snoring was most predictive, more than doubling the risk of developing metabolic syndrome. As expected, insomnia syndrome did not raise the risk of metabolic syndrome.
The study authors were not able to tell if the patients who claimed loud snoring also had the elevated sleep apnea severity as measured by the ApneaLink. This would have been helpful because the authors concluded that loud snoring by itself is a risk factor in developing metabolic syndrome. I'm not convinced that loud snoring without sleep apnea is physically dangerous to patients.
It was interesting that difficulty staying asleep did not significantly raise the metabolic syndrome risk, but difficulty falling asleep did. This goes against my clinical experience of how many sleep apnea patients sleep - most fall asleep easily, but just can not stay asleep. The authors suggested that the difficulty falling asleep could be due to emotional and/or physiologic hyperarousal, which could be due to increase nervous system activity and elevated cortisol levels. These have been linked to insulin resistance and the metabolic syndrome.
For me, the conclusion from this study is that you should seek a sleep evaluation from your doctor if you have loud snoring and/or difficulty falling asleep.