Serum 25(OH)D, PTH and Correlates of Suboptimal 25(OH)D Levels in Persons with Chronic Spinal Cord Injury

STUDY DESIGN: Cross-sectional cohort study. OBJECTIVES: To describe: 1) the prevalence of suboptimal 25-hydroxy vitamin D status (Serum 25(OH)D <75nmol/L) and identify correlates of vitamin D deficiency; and, 2) the prevalence of secondary hyperparathyroidism (Serum intact PTH ≥ 7.0 pmol/L) and identify the relationships between serum parathyroid hormone (PTH) and 25(OH)D in adult men and women with chronic spinal cord injury (SCI). SETTING: Outpatient services, including an osteoporosis clinic at a tertiary spinal cord rehabilitation hospital in Ontario. METHODS: Serum levels of 25(OH)D and intact PTH were acquired at enrolment. Clinical correlates of suboptimal vitamin D status were collected via interview and chart abstraction, and identified by univariate logistic regression analysis. Pearson correlations were run to assess the relationships between serum PTH and 25(OH)D. Significance was p<0.05. RESULTS: Thirty-nine percent of the cohort, comprised of 62 adult men and women with chronic SCI, had suboptimal serum 25(OH)D levels. Factors associated with suboptimal vitamin D levels included having vitamin D assessed in the winter months (OR=7.38, p=0.001), lack of a calcium supplement (OR=7.19, p=0.003), lack of a vitamin D supplement (OR=7.41, p=0.019), younger age (OR=0.932, p=0.010), paraplegia (OR=4.22, p=0.016), and lack of bisphosphonate (OR=3.85, p=0.015). Significant associations were observed between serum PTH and 25(OH)D (r=−0.304, p=0.032) and between PTH and C-telopeptide of type I collagen (CTX-I) (r=0.308, p=0.025). CONCLUSIONS: Disruption of the vitamin D-PTH axis may contribute to the bone loss seen in the chronic SCI population. The threshold for optimal serum 25(OH)D levels in the chronic SCI population may be higher than in the non-SCI population. Serum 25(OH)D level are likely important risk factors contributing to declining bone mass and increased fracture risk post-SCI.