Body Shape Indices and Chronic Knee Pain in Chinese Aging Population: A Longitudinal Analysis of Abdominal Obesity, BMI, and Waist Circumference

Abstract

Background Chronic knee pain (CKP) is a globally prevalent condition among older adults, yet the predictive value of diverse obesity‐related indices for CKP remains insufficiently explored in the Chinese population. This study aims to investigate the longitudinal relationship between abdominal obesity, multiple body shape indices (including weight, body mass index [BMI], waist circumference [WC], visceral adiposity index [VAI], and conicity index [CI]), and the risk of developing CKP using data from the China Health and Retirement Longitudinal Study (CHARLS). Methods We conducted a longitudinal analysis using data from CHARLS Wave 3 (2015, baseline) to Wave 5 (2020). The inclusion criteria were participants aged 55 years or older with complete biomarkers from fasting blood samples and anthropometric data at baseline. We excluded participants who: (1) had missing blood test results or body index data, (2) were lost to follow‐up, (3) had missing information regarding knee pain, and (4) reported pre‐existing knee pain at baseline (Wave 3). Abdominal obesity and body shape indices were assessed at baseline. The incidence of CKP was defined as reporting knee pain in two consecutive follow‐up waves. Logistic regression and restricted cubic splines were employed to evaluate the associations. Results 889 out of 3288 participants, which is 27.04%, were identified as CKP during the 5‐year follow‐up period (2015–2020). After adjusting for various confounding factors, the OR for CKP associated with BMI was 1.03 (95% CI: 1.01–1.05; p = 0.020), WC was 1.01 (95% CI: 1.01–1.02; p = 0.011), and people with abdominal obesity was 1.36 (95% CI: 1.15–1.60; p < 0.001). Subgroup analysis demonstrated similar results without any interactions. In restricted cubic spline regression, the relationship between BMI and CKP is nonlinear, and the relationship between WC and CKP is linear. Conclusions Among middle‐aged and older adults, abdominal obesity, BMI, and WC should be regarded as risk factors of CKP, whereas VAI, CI, and body weight should not. Notably, this study revealed a nonlinear relationship between BMI and CKP, contrasting with the linear link observed between WC and CKP. Furthermore, compared to BMI and WC, abdominal obesity demonstrates a higher statistical effect size and more pronounced clinical significance.