Oxidative stress, reflecting the balance between pro-oxidant and antioxidant influences from diet and lifestyle, has been implicated in cognitive decline. Sleep duration is another modifiable lifestyle factor associated with cognitive health, but its joint relationship with oxidative balance remains insufficiently understood.

This prospective cohort study was conducted in Henan Province, China, based on the Rural Chinese Cohort Study. A total of 4,988 eligible participants aged 60 years or older at the 10-year follow-up were included in the final analysis. The Oxidative Balance Score (OBS) was constructed from dietary and lifestyle components, and cognitive impairment was assessed using the Mini-Mental State Examination at the 10-year follow-up. Multivariate logistic regression models were used to examine the associations of OBS and sleep duration with cognitive impairment. Restricted cubic splines were applied to assess nonlinear associations. Joint and interaction analyses were further conducted to evaluate the combined associations of OBS and sleep duration.

At the 10-year follow-up, 760 participants (15.2%) had cognitive impairment. In the fully adjusted model, compared with the lowest OBS tertile, the highest OBS tertile was associated with lower odds of cognitive impairment ( OR = 0.78, 95% CI : 0.63−0.96), whereas the association for the moderate OBS tertile was not statistically significant. Restricted cubic spline analysis suggested a nonlinear association between OBS and cognitive impairment ( P for nonlinearity = 0.023). Compared with normal sleep duration, both short and long sleep durations were associated with higher odds of cognitive impairment. Joint analyses showed that certain unfavorable combinations of OBS and sleep duration were associated with higher odds of cognitive impairment, particularly short sleep with moderate OBS and long sleep with low OBS. Interaction analysis based on OBS and sleep categories also suggested evidence of interaction ( P for interaction = 0.048). Results remained broadly consistent in sensitivity analyses.

Higher OBS was associated with lower odds of cognitive impairment, whereas both short and long sleep duration were associated with higher odds. Certain unfavorable combinations of oxidative balance and sleep duration were also associated with greater odds of cognitive impairment. These findings support the relevance of considering oxidative balance and sleep duration together in relation to cognitive health in older adults.