OBJECTIVESome research has shown that there is a dose-dependent relationship between ultraviolet B (UVB) and serum levels of 25-hydroxy vitamin D[25-(OH)D]\. Vitamin D is correlated with bone metabolism. This study aimed to explore the effect of UVB irradiation through glass on serum levels of 25-(OH)D and bone metabolism in rats.

METHODSWistar rats were fed with vitamin D deficient diet and randomly divided into three groups: no UVB exposure, direct UVB exposure (160 min/d) and indirect UVB exposure (through glass) (160 min/d). By 21 days after exposure, bone mineral density (BMD) and serum levels of 25-(OH)D, parathyroid hormone (PTH), osteocalcin (OC), bone alkaline phosphatase (BALP) and carboxyterminal cross-linked telopeptide of type I collagen (ICTP) were measured.

RESULTSBMD (0.036+/-0.002 g/cm2) in the indirect UVB exposure group was significantly higher than that in the no UVB exposure group (0.029+/-0.002 g/cm2) (<0.01). Serum ICTP level in the indirect UVB exposure group was significantly lower than that in the no UVB exposure group (0.181+/-0.067 microg/L vs 0.194+/-0.066 microg/L; <0.01). Serum levels of PTH, 25-(OH)D, BALP and OC in the indirect UVB exposure group were not significantly different from those in the no UVB exposure group. Compared with the direct UVB exposure group, serum levels of OC (0.559+/-0.067 ng/mL vs 0.278+/-0.067 ng/mL; <0.05) and PTH (0.181+/-0.067 microg/L vs 0.109+/-0.067 microg/L; <0.05) in the indirect UVB exposure group significantly increased, while serum levels of 25-(OH)D significantly decreased (28.67+/-1.35 nmol/L vs 34.69+/-4.30 nmol/L; <0.01). There were no significant differences in BMD and serum levels of BALP and ICTP between the indirect UVB exposure and the direct UVB exposure groups.

CONCLUSIONSUVB irradiation through glass cannot elevate serum levels of 25-(OH)D, but can decrease bone turnover rate and increase BMD. The effect of UVB irradiation through glass on bone metabolism is similar to that of direct UVB irradiation.