Determinants of Perceived Treatment Effectiveness in Women with Fibromyalgia: A Cross-Sectional Study

Background: Fibromyalgia is a chronic pain syndrome in which treatment effectiveness may be influenced by biological, psychological, social, and nutritional factors. This study aimed to identify clinical, psychosocial, nutritional, and selected individual factors associated with patients' perceived overall treatment effectiveness among women with fibromyalgia. Specifically, we examined whether fibromyalgia symptom severity, psychological and social quality of life, diet quality, vitamin D₃ supplementation, treatment duration, and selected individual characteristics were associated with patients' perceptions of treatment effectiveness. Methods: A cross-sectional online study included 195 women with physician-diagnosed fibromyalgia who reported using medications and/or supplements. Fibromyalgia severity (FAS, FIQR), quality of life in psychological and social domains (WHOQOL-BREF), diet quality (pHDI, nHDI, DQI), vitamin D₃ supplementation, and treatment duration were assessed. Cluster analysis and hierarchical linear regression were performed to identify factors associated with self-perceived treatment effects. Results: Women reporting lower treatment effects presented greater symptom severity, higher FIQR scores, and lower quality of life in psychological and social domains. No significant differences were observed according to age, BMI, diet quality, or self-reported daily vitamin D₃ supplementation. In the final regression model, treatment duration (β = 0.246; p < 0.001), quality of life in the psychological domain (β = 0.173; p = 0.035) and social domain (β = 0.158; p = 0.039), and symptom severity (β = -0.196; p = 0.041) independently predicted self-perceived treatment effects. Conclusions: Better psychological and social well-being, lower symptom severity, and longer treatment duration were associated with higher perceived treatment effectiveness, whereas neither diet quality nor self-reported daily vitamin D₃ supplementation was associated with this outcome. These findings support a multidisciplinary biopsychosocial model of care integrating nutritional, medical, psychological, and social interventions.