Impact of nutritional profile on pain and functionality in patients with frozen shoulder: a cross-sectional observational study

Introduction: Frozen shoulder (FS) is a chronic and painful joint disorder characterized by progressive stiffness and functional limitation. Its multifactorial pathophysiology remains poorly understood, although emerging evidence suggests a role for low-grade inflammation, metabolic dysregulation, and immune-endocrine imbalance. Nutrition and lifestyle factors may therefore represent modifiable contributors to disease development and progression. Methods: This cross-sectional observational study investigated the association between dietary profile, physical activity, pain intensity, and shoulder function in 57 patients with FS (44 women and 13 men). Sociodemographic variables, physical activity levels, adherence to the Mediterranean diet, detailed dietary intake, and shoulder pain and disability were assessed using validated instruments. Multivariate analyses, including Elastic Net and sparse partial least squares regression, were used to identify dietary and lifestyle predictors of pain and functional impairment. Results: Higher consumption of refined carbohydrates, starch, total cholesterol, and processed animal products was associated with worse shoulder function. In contrast, greater intake of specific micronutrients, including thiamine, niacin, iron, manganese, and vitamin D, as well as decaffeinated coffee and higher physical activity levels, was associated with lower pain and disability, particularly in women. Sex-stratified analyses showed stronger and more consistent associations between micronutrient intake and clinical outcomes in women, while predictive modeling in men was limited by sample size. Discussion: These findings suggest the presence of a nutritional pattern associated with symptom severity in FS, supporting a potential immunometabolic contribution to the condition. However, due to the cross-sectional design, causal relationships cannot be established and reverse causation remains possible. These results should be interpreted as hypothesis-generating and highlight the need for longitudinal and interventional studies to determine whether dietary and lifestyle modifications can influence clinical outcomes.