Sleep-disordered breathing (characterized by recurrent arousals from sleep and intermittent hypoxemia) is common among older adults. Previous studies have linked sleep-disordered breathing to poor cognition.  However, it remains unclear whether sleep-disordered breathing precedes cognitive impairment in older adults. Comparing women with or without sleep-disordered breathing, the authors of this study found that individuals with sleep-disordered breathing were more likely to develop mild cognitive impairment or dementia (44.8% versus 31.1%). Measures of sleep fragmentation (arousal index and wake after sleep onset) or sleep duration (total sleep time) were not associated with risk of cognitive impairment.

Yaffe K et al., Sleep-Disordered Breathing, Hypoxia, and Risk of Mild Cognitive Impairment and Dementia in Older Women.     JAMA 306(6): 613-619 (2011).

http://jama.ama-assn.org/content/306/6/613.full