Association of sleep duration and physical frailty with cognitive function in older patients with coexisting atrial fibrillation and heart failure.

The analysis used 176 patients from 277 primary data records, and participants were recruited by convenience sampling at a single centre. The data were cross-sectional, so the study cannot show that sleep duration or frailty caused cognitive impairment. Sleep duration was measured with a single self-reported question, not actigraphy or repeated assessment, and sleep quality and sleep disorders were not measured. Cognitive impairment was screened with MMSE scores below 24, and the authors noted caution because the results rely on patient self-reporting. The analysis adjusted only for age, education, and spouse, and the authors noted that depression and sleep disorders could confound the sleep-cognition relationship. The study did not assess bidirectional relationships, detailed nutritional status, inflammation, dysphagia, dental status, or other biological and psychological factors that could contribute to frailty and cognitive impairment.

The study was funded by the Basic Science Research Program through the National Research Foundation of Korea, with funding from the Korea government. The authors declared no conflicts of interest.

Do not conclude that sleeping 9 or more hours or being frail causes cognitive impairment, or that reducing sleep or treating frailty will improve cognition. This was a cross-sectional study, so it measured associations at one time point and could not establish cause and effect.