Relationships of vitamin D levels in adults with air pollution exposure and total solar radiation in Beijing: a cross-sectional study of health examination participants

Objective To analyze the associations of vitamin D (Vit D) with exposure to air pollution and total solar radiation among adults in Beijing based on clinical data.

Methods Serum 25-hydroxyvitamin D 25(OH)D levels and clinical data were collected from 2 539 subjects (1 428 males and 1 111 females) who underwent physical examination in the Health Management Center of International Medical Department (Xidan Campus) of Peking Union Medical College Hospital from January 2021 to December 2023. Air quality index (AQI) and total solar radiation data of Beijing were obtained simultaneously. Linear regression analyses were conducted by SPSS 27.0 to examine the effects of gender, age, AQI, and solar radiation on serum 25(OH)D levels. Mediating effects were tested with the Bootstrap method.

Results The median serum 25(OH)D level of the 2 539 subjects was 19.40 (14.80, 25.70) ng/mL median (P₂₅, P₇₅). The proportions of subjects with insufficient Vit D and deficient Vit D were 33.01% and 52.42%, respectively. The overall serum 25(OH)D level in females was lower than that in males, and the peak Vit D deficiency rates in males (58.10%) and females (69.29%) both occurred in the age group of 30 to < 40 years. The Kruskal-Wallis test and chi-square test showed that there were statistically significant differences in serum 25(OH)D levels and Vit D deficiency detection rates among different age groups within each gender (all P < 0.001). Linear regression analysis indicated that gender (unstandardized coefficient B = –2.120, t = –5.739), age (unstandardized coefficient B = 0.131, t = 8.028), AQI (unstandardized coefficient B = –0.020, t = –1.993), and total solar radiation (unstandardized coefficient B = 0.027, t = 3.239) were correlated with Vit D levels (all P < 0.05). Mediating effect analysis revealed that total solar radiation played a partial mediating role in the relationship between AQI and Vit D levels (the 95% confidence interval did not include 0).

Conclusions Vit D deficiency is prevalent among adults in Beijing, with a higher deficiency rate in females than in males. AQI is significantly negatively correlated with vitamin D levels, and total solar radiation exerts a partial mediating effect in their relationship. The results suggest that attention should be paid to the impacts of air pollution and solar radiation on Vit D levels.