Mathematical modeling and projection of Vitamin D levels before and during COVID-19: A cross-sectional study including 86.772 samples

Abstract Objective Vitamin D (Vit-D) defined as a steroid hormone produced in the body by exposure of the human skin to UV (ultraviolet) B rays and has important roles in calcium and phosphorus metabolism as well as bone mineralization. In this study, it was aimed to examine Vit-D deficiency not only biologically but also mathematically and produce a mathematical model to determine the level of Vit-D as long as the COVID-19 measures continue. Methods In this study included 86.772 patients samples. Vit-D levels has a wave-curved form with stochasticity in essence. A mathematical modeling has been made for such a curve and this model has been defined. For describing the model MATLAB Curve fitting Toolbox has been used. SSE has been optimized by the Trust-Region algorithm where all the other parameters are selected as default. Results There is no significant difference between sexs according to Vit-D levels (p > .05). It was determined that Vit-D levels were significantly higher in the summer months and lower in the winter months (p < .001). When comparing the spring months, Vit-D levels in 2020 were found to be significantly lower than in 2019 (p < .001); on the contrary, when examined on the basis of summer, autumn, and winter months, it was determined that Vit-D levels increased in 2020 compared to 2019 (p < .001). Conclusion Restrictions, partial or complete closures, and curfews can significantly affect individuals' Vit-D levels during the COVID-19 outbreak. There is a need for multicenter studies with larger populations covering different regions to strengthen and support our results.