Snoring and Risk of Cognitive Decline: A 4‐year Follow‐up Study in 1389 Older Individuals

To the Editor: Studies in clinical samples and in the general population have shown that sleep apnea syndrome is significantly associated with cognitive deterioration and dementia.1, 2The diagnosis of sleep apnea syndrome is based on the number of apnea and hypopnea episodes that are detected by overnight polysomnography. Snoring and excessive daytime sleepiness are frequent clinical symptoms of sleep apnea syndrome. Studies that examined the association between sleep apnea syndrome and cognitive disorders were cross-sectional or case control studies. To our knowledge, there has been only one longitudinal study that did not show any effect of breathing disorders during sleep on cognitive function.3 However, the power of this study was limited by its small size (n = 97) and short follow-up (17 months). In a large cohort of older persons, we examined whether the presence of snoring and excessive daytime sleepiness are risk factors at baseline for cognitive decline at 4-year follow-up. The EVA study is a longitudinal study investigating age-related cognitive and vascular disorders. The study population consisted of 574 men and 815 women, aged 59 to 71 years, recruited from the electoral rolls of Nantes (France). Data regarding education, occupation, medical history and drug use, and alcohol and tobacco consumption were collected using a standardized questionnaire. Physical examination included weight, height, and blood pressure measurements. Depressive symptoms were scored using the Center for Epidemiologic Study Depression (CES-D) scale. Data in regard to snoring and excessive daytime sleepiness were collected using a self-report questionnaire that has been previously validated.4The Mini-Mental State Examination (MMSE) was administered at baseline and 4 years later (follow-up rate: 88%). Cognitive decline was defined as a MMSE decrease of 3 points or more. To estimate the relative risk of cognitive decline associated with snoring or excessive daytime sleepiness, we computed odds ratios using multivar-iate logistic regression analysis. At baseline, 61.7% of men and 40.9% of women reported regular snoring, and 33.1% of men and 22.0% of women complained of inordinate daytime sleepiness. Snoring was related to body mass index (BMI), high blood pressure, and alcohol consumption, but only in men. Excessive daytime sleepiness was related to BMI, high blood pressure, and depressive symptomatology, but not to psychotropic drugs. All analyses were adjusted for age, gender, educational level, BMI, high blood pressure, and initial value of the MMSE. The possible confounding effect of alcohol consumption and depressive symptoms was also taken into account. A total of 184 subjects (16%) had a decrease in MMSE score of 3 points or more between baseline and 4-year follow up examinations. Longitudinal analyses showed that snorers had an increased risk of cognitive decline compared with non-snorers (OR = 1.36; 95% CI, 0.97-1.92); a similar trend was found for excessive daytime sleepiness (OR = 1.33; 95% CI 0.93-1.90). In the cross-sectional analysis of the EVA study data, we found that symptoms of breathing disorders during sleep were associated with low cognitive scores.1This previous finding is confirmed by the longitudinal analysis presented here, which showed that snoring and excessive daytime sleepiness were risk factors for cognitive decline Sleep apnea syndrome can be responsible for high blood pressure,5 which is a significant risk factor for cognitive decline in older people,6 but these relationships cannot explain our findings because the possible confounding effect of high blood pressure was taken into account in all analyses. Other mechanisms that could explain the relationship between symptoms of breathing disorders during sleep and accelerated cognitive decline are sleep fragmentation, reduction of duration of deep sleep, and nighttime hypoxemia. These chronic disorders could have a deleterious effect on cognitive functioning of older individuals.