Sleep Apnea vs Cognitive Fxn: Chicken or Egg?

Sleep-disordered breathing is a collection of disorders most typified by sleep apnea.  It is characterized by recurrent (micro)arousals and intermittant hypoxemia.  In other words, individuals who suffer from sleep-disordered breathing wake up many times each night mainly because they're not getting enough oxygen (air).  This is most commonly associated with snoring, although it's actually that blessed silence that's deadly as that is when the patient is struggling to open the breathing passage to get air in and can't, thus the silence.  Typically, the longer the silent pause, the lower one's oxygen level drops, thus disturbing one's sleep just enough to wake enough to change sleeping position and open up one's airway. 

So why is this important?  In men, sleep-disordered breathing has been associated with all-cause mortality and sudden cardiac death.  And in a new prospective study released this week in the Journal of the American Medical Association, the authors linked sleep-disordered breathing with mild cognitive impairment and dementia in older women.  Just how did they do this?  The authors followed 193 women w/o sleep-disordered breathing and another 105 w/sleep-disordered breathing for almost 5 years.  The presence or absence of sleep-disordered breathing was confirmed via a sleep study or overnight polysomnography using an apnea-hyponea index of 15 or greater as diagnostic of the condition. 

Baseline cognitive function was assessed such that all of these individuals had normal cognitive function at the beginning of the observation period.  However, after 5 years time, the authors noted that those women with sleep-disordered breathing had an increased risk of developing mild cognitive impairment or dementia compared to women w/o sleep-disordered breathing.  So this proves the link between the two conditions but more importantly demonstrates that sleep-disordered breathing pre-dates mild cognitive impairment and death.  Unfortunately this still isn't enough to demonstrate cause & effect, similar to the ongoing conundrum regarding the chicken and the egg.  There's remains an alternative thought process that perhaps the brain dysfunction leads to the breathing issue.  The $64,000 question is whether treating sleep apnea & hypoxemia will improve/prevent mild cognitive impairment and dementia.  Time will tell . . .