Low vitamin D levels are independent predictors of 1-year worsening in physical function in people with chronic spinal cord injury: a longitudinal study

Study design: Longitudinal cohort study. Objective: To explore the longitudinal association of baseline vitamin D levels with 1-year change in physical function outcomes in people with chronic spinal cord injury (SCI). Setting: Rehabilitation institute. Methods: Sixty-seven patients (44 men and 23 women) with chronic SCI admitted to a rehabilitation program were included. Functional independence in daily living activities (as evaluated by the Spinal Cord Independence Measure version III, SCIM III) and leisure time physical activity (LTPA) were assessed as measures of physical function at the admission and re-assessed 1-year later. Comorbidity was scored by Charlson comorbidity index (CCI). Results: A 1-year worsening in SCIM and LTPA were registered in 44 and 40 patients (66% and 60% of the study population), respectively. They exhibited significantly lower baseline 25(OH)D levels, higher CCI, and shorter distance from the injury. At the multiple linear regression analyses, lower baseline 25(OH)D levels exhibited a significant independent association with higher percentages of 1-year worsening in both SCIM and LTPA. At ROC analysis, baseline 25(OH)D levels <18.6 and <18.2 ng/mL discriminated individuals with 1-year worsening in SCIM and LTPA, respectively. According to these cut-off points, at the multiple logistic regression analysis, patients with low baseline 25(OH)D levels exhibited an OR of worsening in SCIM and LTPA engagement 2.8- and 2.6-fold higher, after adjustment for CCI, distance from injury, and post-follow-up 25(OH)D levels. Conclusions: In people with chronic SCI, a low 25(OH)D level may represent an independent predictor of worsening in physical function outcomes over time.