Short-range ultraviolet irradiation with LED device effectively increases serum levels of 25(OH)D

Impairment of the activities of daily living (ADL) by osteoporosis is an important concern in developed countries with a super-aging population. Vitamin D, which is a crucial molecule in bone metabolism and mainly produced endogenously with ultraviolet (UV) light exposure, is known to be insufficient in the elderly population. We used an UV Light-Emitting Diode (UV-LED) instrument generating a narrow-range wavelength to analyze the efficacy of endogenous vitamin D production. The primary purpose of this study was to examine the effects of UV irradiation at various narrow-range wavelengths using UV-LED on vitamin D supplementation. The second one was to clarify the short-term effects of UV irradiation on bone morphology in mice. Vitamin D-starved C57BL/6 female mice (n = 7 per group) were UV-irradiated (268 nm, 282 nm, 290 nm, 305 nm, and 316 nm) with 1 kJ/m2 twice a week for 4 weeks. UV irradiation using UV-LED had significant effects on increasing serum 25(OH)D levels in all wavelength groups (P < 0.001, all groups) as compared to a control group. Among irradiated groups, wavelength of 316 nm had a less marked effect on 25(OH)D production compared with other wavelengths at 1 week of UV irradiation (P < 0.05). Levels of 1,25(OH)2D were significantly increased after 4 weeks irradiation with UV-B or UV-C irradiation (P < 0.05). mRNA levels of vitamin D 25-hydroxylase were increased with UV-B or UV-C irradiation (268 nm-305 nm), significantly. Micro-CT examination revealed that short-term (4 weeks) UV-irradiation did not induce morphological change of mice in any group. This study provides essential information that narrow-range UV irradiation with LED can increase the endogenous production of vitamin D, and mRNA levels of the responsible enzyme. Although bone morphology was not altered by short-term UV irradiation in this study, an increase of serum vitamin D might improve bone morphology with long-term irradiation.