High burden of vitamin D deficiency in Chinese university students: impact of sun protection culture.

BACKGROUND: Vitamin D serves a critical function in preserving human physiological well-being and is mainly synthesized within the skin through sunlight exposure. In China, the traditional cultural preference for fair skin is associated with widespread sun avoidance among many individuals, including university students, who seek to prevent skin tanning. Although sun protection habits and fair-skin pursuit are widely prevalent in China, their associations with vitamin D inadequacy have not been well clarified in the college student demographic. METHODS: The present cross-sectional investigation was conducted from May to June 2025 in Hangzhou, using convenience sampling to enroll 174 regular university students and 17 outdoor-trained students as controls. Blood biochemical detection analyses were conducted to measure circulating 25(OH)D concentrations and bone turnover indicators, while standardized questionnaires were adopted to gather data on participants' sun protection habits and skin color aesthetic preferences. Multiple linear regression models were constructed with adjustment for age, sex, BMI, daily sun exposure duration, physical activity level, and smoking and drinking status. RESULTS: A total of 93.10% of the usual students had vitamin D deficiency (<50 nmol/L), among whom 59.20% were deficient (<30 nmol/L). These rates were considerably higher than those observed in outdoor students (29.41 and 23.53%, respectively). In the 174 regular university students, Pearson correlation analysis showed a significant negative association between sun protection behavior scores and serum 25(OH)D concentrations (r = -0.387, p < 0.001). This association remained significant after adjusting for age, BMI, sex, and sun exposure time in multiple linear regression models. Additionally, the study population generally exhibited a cultural preference for fair skin, which was also significantly associated with lower serum 25(OH)D levels. CONCLUSION: Chinese university students have a strikingly elevated prevalence of vitamin D insufficiency and deficiency, which is closely linked to excessive sun protection related to traditional fair-skin aesthetic norms. The present results reveal a notable contradiction between skin aesthetic pursuits and skeletal health status, suggesting that culturally tailored intervention strategies are essential for improving vitamin D levels among young adult populations.