Association Between Daily Internet Use and Intrinsic Capacity Among Middle-Aged and Older Adults in China: Large Prospective Cohort Study
Authors: Chen Xing-Ling , Li Jin , Sun Shu-Ning , Zhao Qiang-Qiang , Lin Sheng-Rong , Wang Ling-Jun , Yang Zhong-Qi , Ni Shi-Hao , Lu Lu 
Published: October 2024

Background
Intrinsic capacity (IC), as a comprehensive measure of an individual’s functional ability, has gained prominence in the framework for healthy aging introduced by the World Health Organization (WHO). As internet usage continues to integrate into daily life, it is imperative to scrutinize the association between internet use and IC to effectively promote healthy aging among the middle-aged and older population.

Objective
This study aimed to investigate whether daily internet use in middle-aged and older adults delays or accelerates the decline in IC.

Methods
Participants included in the China Health and Retirement Longitudinal Study (CHARLS) comprised individuals aged ≥45 years residing in China. We analyzed 4 years of CHARLS data from the first wave (May 2011-March 2012) to the third wave (July 2015-January 2016). Data from the first and third waves were used for longitudinal studies. Self-reported data encompassed internet use, frequency of use, and demographic baseline characteristics. In addition, the IC evaluation involved physical examination and blood test data. Initially, linear regression was used to assess the relationship between daily internet use and IC, followed by regression splines to explore potential nonlinear associations. Subgroup and sensitivity analyses were used to investigate the heterogeneity of IC in specific conditions and the robustness of our results. Mediation effect analysis was conducted to identify the factors that mediate the relationship between daily internet use and IC, focusing on social participation, physical activity, and health status.

Results
Among the 12,826 participants included in the longitudinal analyses, 12,305 (95.9%) did not use the internet, while 521 (4.1%) reported daily internet use with a mean age of 52.62 (SD 7.67) years. After adjusting for demographic variables, socioeconomic factors, lifestyle behaviors, and health conditions and examining the impact of daily internet use and frequency on changes in IC, our findings indicated important associations. Specifically, daily internet use is significantly linked to a slower decline in IC over time (marginal effect 1.58, 95% CI 1.03-2.12; P<.001). Individuals with moderate and regular internet use frequency exhibit higher levels of maintenance in IC (marginal effect 0.74, 95% CI 0.45-1.03, P<.001). In addition, the relationship between IC changes and internet use frequency demonstrated a nonlinear inverted U-shaped curve (nonlinear P=.003). Subgroup analysis further revealed that improvements in IC vary based on age and gender. Furthermore, mediation analysis denoted that more than 28.78% (95% CI 21.24-40.33) of the observed association is mediated by social participation (P<.001).

Conclusions
The findings of our research underscore the potential benefits of consistent and moderate internet use in promoting and preserving IC, particularly in cognitive capacity, sensory, vitality, and locomotion. The observed effects may be related to social participation. These insights offer valuable guidance for crafting strategies aimed at fostering healthy aging within the middle-aged and older adult demographics.