Interpreting wrist actigraphic indices of sleep in epidemiologic studies of the elderly: The study of osteoporotic fractures

Introduction: Although wrist actigraphy-derived sleep indices correlate with adverse health outcomes, it is unclear whether these indices identify specific sleep disorders. Methods: Overnight polysomnography and ≥ three 24-h periods of wrist actigraphy were performed in the Study of Osteoporotic Fractures (SOF) (n = 455, age: 73-96 y). Actigraphy identified those with reduced sleep efficiency (SE, < 70%) and decreased sleep duration (≤ 5 h). Sleep disorders considered were: (1) sleep-disordered breathing (SDB): respiratory disturbance index ≥ 15 and (2) periodic limb movement disorder (PLMD): periodic limb movement-arousal index ≥ 5. Multivariable logistic regression analyses modeled each sleep disorder as the dependent variable with wrist actigraphy measures, age, race, medication use, depression, body mass index, activity, mental status, and comorbidity as independent variables. Results: In multivariable models, poor SE derived from wrist actigraphy was associated with 2.4-fold higher odds of SDB (OR = 2.43, 95% CI: 1.43-4.14) and PLMD (OR = 2.36, 95% CI: 1.34-4.15). Reduced sleep duration was associated with 3.2-fold higher odds of SDB (OR = 3.18, 95% CI: 1.51-6.68), and a 3.8-fold higher odds of PLMD (OR = 3.77, 95% CI: 1.78-7.95). Conclusions: In elderly women, wrist actigraphy-ascertained reduced SE and sleep duration are associated with objective measures of SDB and PLMD. Thus, although not able to discriminate between the different sleep disorders, variations in wrist actigraphy measures collected in epidemiologic studies may identify individuals at higher risk of SDB or PLMD.