Effect of ultraviolet irradiation dose and style on 25-hydroxyvitamin D and bone metabolism in growing rats

Wei ZHANG; Liwen CHANG; Shurong WANG; Wei WU

ABSTRACT

BACKGROUND:

Sunshine time in northem region is short in winter,the infants and young children are vulnerable to lack of vitamin D. Up-to-date textbooks and the guidelines formulated by Chinese Medical Association account that glass block ultraviolet and indoor exposure to human is meaningless. Early studies have shown that sunlight exposure through glass had meaning in rats,but it was difficult to accurately quantify,while outdoor exposure in rats is difficult to continue. This expedment uses B-band ultraviolet rays,which has the impact on vitamin D metabolism in some wavelengths,to facilitate further study.

OBJECTIVE:

To study the effect of ultraviolet B exposure in laboratory on 25-hydroxy vitamin D(25-OHD)level and bone metabolism in the serum of growing rats.DESIGN,TIME AND

SETTING:

A randomized controlled animal experiment was performed in June 2007 in the ExperimantalAnimal Center of Chinese PLA General Hospital.MATERIALSForty male 21-day-old Wistar rats were employed in this study. Ultraviolet waves were sourced from an artificial UV light instrument(wavelength 280-350 μm,irradiation intensity 5.5μW/cm~2).

METHODS:

Forty Wistar rats were divided into four groups by random sampling table,exposed to different doses of ultraviolet Bwave. Direct exposure groupdirect exposure for 20 minutes at an irradiation dose of 4.2 mJ/(cm~2·d);Indirect exposure 60 and 120 min groupsexposure through a single pane of glass for 60 and 120 minutes at an irradiation dose of 0.36 and 0.72 mJ/(cm~2·d).Control groupno exposure was given. For the direct exposure group,the lamp was placed above the cage. A 3-mm-thick pane of glass(common window glass) was placed underneath the lamp in the indirect exposure groups. Exposure groups were given irradiation for successive 20 days.MAIN OUTCOME

MEASURES:

Serum 25-OHD,bone alkaline phosphatase (BALP),and bone mineral density (BMD) were measured on day 21.

RESULTS:

25-OHD was significantly higher in all exposure groups compared with the control group (P＜0.001),but there was no difference between the direct exposure group and two indirect exposure groups. BALP was significantly lower in the exposure groups than control group (P＜0.001),it was also significantly lower in the 120-min indirect group than in the 60-min indirect group (P=0.022). There was a positive correlation between exposure dose and 25-OHD (r=0.555,P=0.002) and a negative correlation between exposure dose and BALP (r=0.595,P=0.001),also a negative correlation between 25-OHD and BALP (r=0.569,P=0.002),but there were no differences between groups for BMD. Exposure dose exhibited a threshold,serum 25-OHD and BALP no longer increased or decreased when it was 0.36 mJ/(cm~2·d).

CONCLUSION:

Midwave ultraviolet rays might affect serum 25-OHD and BALP levels in the growing rats through glass exposure,with no significant difference compared to direct exposure. The B-band ultraviolet exposure dose may play an important role in serum 25-OHD synthesis,but there is a threshold dose for the synthesis. Low-dose and prolonged exposure time also achieve threshold exposure.