Musiek ES, et al. - The associations between circadian function, aging, and preclinical Alzheimer's disease (AD) pathology were investigated in cognitively normal adults. Independent of age or sex, the preclinical AD was correlated with rest-activity rhythm fragmentation. In addition, aging was associated with circadian dysfunction independently of preclinical AD pathology, especially in men. In the preclinical phase of AD, the presence of circadian rhythm abnormalities suggested that circadian dysfunction could contribute to early disease pathogenesis or serve as a biomarker of preclinical disease.