Seasonal variations in serum levels of vitamin D and other biochemical markers among KSA patients prior to thyroid surgery

Objectives: Serum levels of vitamin D can vary between seasons, which may affect serum calcium levels in post-thyroidectomy patients. This study aimed to determine seasonal variations in serum levels of vitamin D and other biochemical markers in patients prior to thyroid surgery in a KSA hospital. Methods: In this study, we analysed the data of 685 post-thyroidectomy patients. The preoperative laboratory values of all patients were collected, and the patients were categorized into groups based on the month when the surgical procedure was performed as follows: cold (November–February) and warm/hot groups (March–October). Results: Serum vitamin D levels were deficient in 70% of the patients, insufficient in 18%, and optimal in 12%. The mean age of patients in the deficient group was significantly lower than that in the optimal group. There were significantly more patients who had vitamin D deficiency during the cold season than during the warm/hot season (p = 0.024). Serum vitamin D levels did not vary between seasons (p = 0.836); however, the preoperative magnesium and thyroid stimulating hormone (TSH) levels were significantly higher during the warm/hot season than during the cold season (p = 0.039 and p < 0.001, respectively). Preoperative calcium level was not significantly different between the cold and warm/hot months (p = 0.282). Conclusion: This study suggests a non-significant seasonal fluctuation in serum levels of vitamin D with insignificant variation in serum calcium levels during cold and warm/hot seasons. The findings necessitate a careful review of the patients’ biochemical status prior to surgery. Future prospective longitudinal studies are needed to confirm this variability.