Intrinsic capacity (IC), a multidimensional construct encompassing mental and physical capacities, has been established in the aging framework by the World Health Organization. However, the detailed relationship between IC and Chinese sleep patterns (nighttime sleep and post-lunch naps) remains inadequately elucidated.

Participants in this study were individuals aged ≥45 years residing in China, included in the China Health and Retirement Longitudinal Study (CHARLS). We analyzed 4 years of CHARLS data from the first wave (May 2011 - March 2012) to the second wave (July 2015 - January 2016). Data from these waves were utilized for longitudinal analysis. Self-reported data included nighttime sleep and nap duration, along with other baseline characteristics. The IC evaluation involved physical examinations and blood tests. Initially, linear regression was used to assess the relationship between total sleep duration, nighttime sleep duration, nap duration, and IC change between the two waves that were determined by marginal effects (ME) and their corresponding 95% confidence intervals (CIs). Regression splines were employed to explore potential nonlinear associations. Subgroup and sensitivity analyses were conducted to investigate the heterogeneity of IC change under specific conditions and the robustness of our results. Mediation analysis was performed to identify potential factors mediating the relationship between sleep patterns and IC change.

Both excessive (>10 hours) (total, ME: -1.12; 95% CI: −1.61, −0.64; nighttime, ME: -1.44; 95% CI: −2.29, −0.59) and insufficient (<6 hours) sleep duration (total, ME: -0.43; 95% CI: −0.68, −0.18; nighttime, ME: -0.50; 95% CI: −0.73, −0.27) negatively impacted IC change. Moderate naps (≤60 minutes) mitigated the decline in IC change (ME: 0.28; 95% CI: 0.07, 0.49). IC values decreased at the slowest rate when nap time constituted one-seventh of total sleep time. The onset of dyslipidemia partially mediated the association between naps (≤ 60 minutes) and IC change (P =  0.02).

These findings suggest that maintaining a healthy sleep pattern of 6-8 hours of nighttime or total sleep, along with a post-lunch nap of ≤60 minutes, helps preserve optimal IC or delay its decline. This is particularly beneficial for cognitive, psychological, and locomotion performance among middle-aged and older adults.