Seasonal Variation of Vitamin D, PTH, and Bone Turnover Markers in Patients Undergoing Lumbar Fusion Surgery

Secondary analysis of a prospective cross-sectional study at an academic tertiary spine care center.

To examine the prevalence and risk factors for preoperative Vitamin D (VitD) deficiency and secondary hyperparathyroidism (SHPT), and to assess the seasonal variation of metabolic bone laboratory parameters in patients undergoing lumbar fusion surgery (LFS).

LFS relies on adequate connective tissue quality and bone healing capacity. VitD deficiency and SHPT significantly impact bone metabolism and are linked to lower fusion rates and poorer bone quality. However, their seasonal variation in LFS patients remains unexplored.

Patients undergoing LFS for degenerative conditions received preoperative VitD, parathyroid hormone (PTH), and bone turnover markers laboratory routinely from December 2014 to December 2023. Descriptive and comparative statistics, logistic regression, and univariable and multivariable cosinor regression models were used to evaluate VitD status, SHPT prevalence, their risk-factors and seasonal variations in VitD, PTH, and bone turnover markers.

Data from 431 patients (49% female, median age 64 y) was analyzed. VitD insufficiency (<30 ng/mL) was observed in 34% of patients, ranging from 48% in winter to 25% in summer. SHPT was present in 24%, with winter prevalence at 28%. Surgery during winter and spring was associated with a 7.5-fold increased risk of VitD deficiency and a 2.1-fold increased risk of SHPT. Seasonal changes with peaks for VitD, PTH, and bone-specific alkaline phosphatase were observed in July, February, and November, respectively, with no significant annual variation in other bone metabolism markers.

The prevalence of VitD deficiency and SHPT in LFS patients is high, especially during winter and spring. Seasonal variations in VitD and bone metabolism markers suggest that single-timepoint laboratory evaluations may not reflect bone metabolism throughout the year, highlighting the need for further studies investigating whether seasonal factors in preoperative assessments could affect outcomes.