OBJECTIVES: Sleep disordered breathing (SDB) is very common in older people and is known to be associated with complaints of impaired daily functioning, including excessive daytime sleepiness and cognitive impairments. As part of a larger study on SDB and aging, it became possible to examine the relationship between SDB and cognition in older men and women.
DESIGN: A population-based longitudinal study.
SETTING: In-home interviews and home sleep recordings in the greater San Diego area.
PARTICIPANTS: Community-dwelling people age 65 and older with high risk for SDB were originally studied from 1981 through 1985 and then followed every 2 years. Data from the 46 subjects who completed Visit 3 and Visit 4 are presented.
MEASUREMENTS: Subjects were interviewed in the home about their sleep and medical condition before each visit. Cognitive function was assessed using the Mini-Mental State Examination (MMSE). Daytime sleepiness was based on self-report. Objective sleep was recorded in the home and scored for sleep, apneas and hypopneas, and oximetry variables.
RESULTS: Increases in respiratory disturbance index (RDI) (P = .036) and increases in daytime sleepiness (P = .002) were associated with decreases in cognitive performance (i.e., increases in cognitive impairment). Increases in RDI were also associated with increases in daytime sleepiness (P = .012). Change in MMSE scores was therefore regressed onto changes in RDI, daytime sleepiness, age, and education, resulting in decreases in MMSE scores being associated with increases in daytime sleepiness (P = .019) but not with changes in RDI (P = .515). There was no significant relationship between changes in oxygen saturation levels and changes in MMSE.
CONCLUSIONS: The results of this study suggest that declining cognitive function is associated primarily with increases in daytime sleepiness. Although cognitive decline was also associated with increases in RDI, this association did not hold in the more inclusive model which also included variable of SDB, oximetry, sleep and subjective report. One theoretical model could suggest that any relationship between SDB and cognitive function may be mediated by the effect of SDB on daytime sleepiness. These results suggest that older patients suffering from mild to moderate SDB may benefit from the treatment of SDB, even if they are not markedly hypoxemic.