Association Between Relative Fat Mass and New-Onset Arthritis Among Middle-Aged and Older Chinese Females

Arthritis is a major health concern in middle-aged and older people. In females, estrogen decline after midlife may exacerbate abnormal adiposity and thereby heighten arthritis risk. Given China's large population, clarifying the relationship between fat mass and arthritis in middle-aged and older Chinese females is of great public-health importance. To explore the relationship between relative fat mass (RFM) and incident arthritis in middle-aged and older Chinese females. This population-based longitudinal study included 3874 females from the China Health and Retirement Longitudinal Study. Logistic regression and restricted cubic splines (RCS) evaluated the relationship between RFM and arthritis. Subgroup and interaction analyses explored potential heterogeneity across age groups and subgroups defined by chronic disease status. After full adjustment, females in the third (Q3 OR = 1.70, 95% CI: 1.24-2.33, <i>P</i> < 0.001) and fourth (Q4 OR = 1.67, 95% CI: 1.13-2.47, <i>P</i> = 0.010) RFM quartiles exhibited significantly higher odds of incident arthritis compared with those in the lowest quartile (Q1). Across the full study population and within the stratum of women below 60 years, RCS disclosed a statistically significant association between arthritis risk and RFM (<i>P</i>_overall < 0.05), with no indication of nonlinearity (<i>P</i>_nonlinear > 0.05). Subgroup analyses revealed no evidence of effect modification (<i>P</i>_interaction > 0.05). Higher levels of RFM are associated with increased risk of new-onset arthritis in middle-aged and older Chinese females, providing a crucial indicator for the early screening of female arthritis and indicating a potential for controlling arthritis incidence by targeted body fat management.