Objective: To explore the association between obesity and cognition impairment in patients with moderate-to-severe obstructive sleep apnea-hypopnea syndrome (OSAHS).
Methods: A total of 425 eligible patients with moderate-to-severe OSAHS were screened for this retrospective study at Sleep Center, Second Affiliated Hospital, Soochow University from January 2008 to January 2013. Based on body mass index (BMI), they were categorized into normal weight (18.5 ≤ BMI<24, n = 67), mild overweight (24 ≤ BMI<26, n = 100), severe overweight (26 ≤ BMI<28, n = 134) and obese (BMI ≥ 28, n = 124) groups. They were examined by overnight polysomnography (PSG). And cognitive functions were assessed by the Montreal Cognitive Assessment (MoCA) questionnaires. MoCA scores, clinical and polysomnographic variables were compared between the groups. And the correlations between MoCA scores and clinical and PSG parameters were further evaluated by stepwise multivariate regression. Two-way analysis of variance (two-way ANOVA) was performed to examine the effects of obesity and OSAHS on MoCA score.
Results: The scores of MoCA progressively decreased across the spectrum from mild overweight to obese groups. The highest BMI group (obese group) had the lowest MoCA score (25.45 ± 2.35 vs 26.26 ± 2.01, 26.29 ± 2.60, 26.05 ± 2.51, P = 0.030, 0.010, 0.048). The evaluations of MoCA subdomains further revealed selective reductions. Compare to normal weight group, the score of visuospatial and executive function, memory/delayed recall significant decreased in obese and severe overweight groups (visuospatial and executive function: 4.48 ± 0.63 vs 4.07 ± 0.94, 4.13 ± 1.04, P = 0.022, 0.048; memory/delayed recall: 3.54 ± 0.90 vs 2.77 ± 1.20, 2.87 ± 1.30, P = 0.001, 0.004). Stepwise multivariate regression analysis demonstrated that MoCA scores were correlated significantly with apnea-hypopnea index (AHI), BMI, age and years of education. Two-way ANOVA revealed that both obesity and OSAHS had independent effects on MoCA score (P = 0.004). The interactions between the effect of obesity and OSAHS on cognitive score were insignificant. It indicated that the effect of BMI on cognitive function did not change with AHI.
Conclusions: In OSAHS patients, obesity aggravates cognitive impairment independently of AHI. And obesity is one of the most important influencing factors of cognitive function.