Association of muscle strength and body weight with late-life insomnia: Underweight spectrum in aging

STUDY OBJECTIVES: This territory-wide cross-sectional study examined joint associations of muscle strength and body weight status with late-life insomnia. METHODS: Insomnia was identified using the Insomnia Severity Index. Muscle strength was measured using handgrip strength. Body weight status was assessed via body mass index, waist circumference, and body fat percentage. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: Among 5824 older adults aged ≥60 years (77.8% female), 696 (12.0%) participants had insomnia. Clinically defined low muscle strength was associated with significantly higher odds of insomnia [1.22 (1.02-1.46)], after adjustment for potential confounders including depressive symptoms. The ORs (95% CIs) of insomnia increased progressively from highest to lowest quartile of muscle strength [1.00 (reference), 1.15 (0.89-1.47), 1.15 (0.90-1.48), and 1.56 (1.22-1.99)]. Compared with normal weight, only underweight was associated with higher odds of insomnia [1.66 (1.18-2.34)], while overweight or obesity did not. In joint analyses, compared with normal muscle strength and normal weight group (i.e., the optimized reference), low muscle strength was associated with significantly higher odds of insomnia in normal weight [1.47 (1.08-1.99)] and underweight [2.27 (1.46-3.50)] groups. Among participants with normal muscle strength, neither underweight [2.29 (1.16-4.55), Bonferroni-corrected p = .053] nor overweight/obese group showed significantly higher odds of insomnia [1.30 (0.95-1.77)]. Underweight combined with low muscle strength consistently showed largest absolute risk differences in predicted probability of insomnia (6.3% ~ 10.6%). CONCLUSIONS: Underweight and low muscle strength were independently associated with insomnia, with their co-occurrence showing highest prevalence of insomnia.