# Bidirectional association between symptomatic knee arthritis and circadian syndrome among middle-aged and older population: an analysis from the China health and retirement longitudinal study

## TL;DR

This study finds that knee arthritis and circadian syndrome can influence each other over time in middle-aged and older adults.

## Contribution

The study reveals a bidirectional relationship between symptomatic knee arthritis and circadian syndrome using longitudinal data.

## Key findings

- Symptomatic knee arthritis increases the risk of developing circadian syndrome (OR = 1.58).
- Circadian syndrome increases the risk of developing symptomatic knee arthritis (OR = 1.52).
- Bidirectional associations were confirmed using cross-lagged path analysis (β1 = 0.05, β2 = 0.07).

## Abstract

Increasing evidence has shown that there was an association between arthritis and metabolism and circadian rhythms. Circadian syndrome (CircS) can serve as an overarching indicator of circadian and metabolic disturbances. However, there are limited studies investigating the longitudinal association between the symptomatic knee arthritis and circadian syndrome (CircS).

This study used the data from two waves (2011 and 2015) of the China Health and Retirement Longitudinal Study (CHARLS). CircS was diagnosed when participants exhibited four or more of the following specified components: short sleep, depression, abdominal obesity, hyperglycemia, hypertension, and dyslipidemia. Symptomatic knee arthritis was diagnosed when both concurrent pain in knee joint and physician-diagnosed arthritis existed. Individuals diagnosed with CircS in 2011 were excluded from the symptomatic knee arthritis group, and those with symptomatic knee arthritis in 2011 were excluded from the CircS group. Each group was followed up for four years to observe the incidence of CircS and symptomatic knee arthritis, respectively. Binary logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for the longitudinal association between the symptomatic knee arthritis and CircS. Cross-lagged path analysis model was further conducted to estimate the bidirectional relationship. All models were considered to adjust for potential confounders.

At the baseline, 5525 non-CircS individuals and 9773 individuals without symptomatic knee arthritis were included in this study, respectively. During 4-year follow-up, 1278 CircS and 950 symptomatic knee arthritis new cases were observed respectively. After adjusting for potential confounders, symptomatic knee arthritis was associated with increased risk of CircS (OR = 1.58, 95% CI: 1.24–2.02). CircS was associated with increased risk of symptomatic knee arthritis (OR = 1.52, 95% CI: 1.31–1.76). Cross-lagged path analysis showed that the symptomatic knee arthritis significantly affected the incidence of CircS (β1 = 0.05, 95% CI: 0.03–0.07, P < 0.001), and vice versa (β2 = 0.07, 95% CI: 0.05–0.09, P < 0.001).

Significant bidirectional associations were identified between the symptomatic knee arthritis and CircS. Interventions should be developed to prevent the development or progression of both symptomatic knee arthritis and CircS.

The online version contains supplementary material available at 10.1186/s12889-025-25100-1.