Effects of power density and beam type for ultraviolet B on photoconversion of 7-dehydrocholesterol (7-DHC) into previtamin D3

Vitamin D is a group of fat-soluble secosteroids for increasing intestinal absorption of calcium, magnesium, and phosphate, and is related with other biological effects. The most important compounds of vitamin D for humans are vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol), both of which can be ingested from the diet and supplements. The present study aimed to provide the optimized selection in power density and beam type for this problem. The light-emitting diode (LED) source with a peak wavelength of 284 nm was used to illuminate 7-DHC in different power density and beam type, and then the conversion rate was tested based on high performance liquid chromatography (HPLC). The used irradiated conditions include the 5, 10, 15 and 20 mW/cm2 , the used frequency includes 0.1, 1, 10 and 100 Hz, and the duty cycle includes 20%, 40%, 60% and 80%. Our results show that there is no obvious difference between the different irradiation for the used continuous light with the same dose of 200mJ/cm2 , but the conversion rate of pulse light source increases with the increasing of power density. Besides, compared with the continuous light source, the pulse light source has no better conversion effect. The conversion rate decreases with the increasing of pulse frequency from 1 Hz to 100 Hz. Moreover, duty cycle does not affect conversion rate for 7-DHC to previtamin D3. Only If the irradiation is altered, the conversion rate against to duty cycle will be changed. The power density indirectly affects the conversion rate through penetration depth, and the continuous illumination mode is better than the pulse illumination mode. This paper can help to up-regulate serum vitamin D level to patients with fat malabsorption syndromes as well as patients with other metabolic and hence to stimulate the application of artificial light sources like LED in health care.