Vitamin D Status and Its Influencing Factors in Zhejiang Province: A Multicenter Cross-Sectional Study

Vitamin D deficiency is a global public health problem, with an estimated 1 billion people affected worldwide, and large-scale systematic data for Zhejiang Province remain scarce. This is a multicenter, retrospective cross-sectional study. The objectives are to: (1) assess the distribution of serum 25-hydroxyvitamin D \[25(OH)D\] levels across regions, seasons, and demographic groups in Zhejiang Province and estimate the prevalence of vitamin D deficiency (\<20 ng/mL) and insufficiency (20-29 ng/mL); (2) identify and quantify key determinants of vitamin D status, including environmental exposures (ultraviolet radiation, green coverage), lifestyle (outdoor activity, sun protection), dietary vitamin D intake, and individual characteristics; and (3) provide scientific evidence for targeted intervention strategies, public health policy, and clinical guidelines in Zhejiang Province.