X-ray-mediated vitamin D synthesis.

Vitamin D synthesis is traditionally linked to ultraviolet B (UVB) light exposure of its precursors 7-dehydrocholesterol and ergosterol. This study investigated whether ionizing X-ray irradiation can also induce the conversion of sterol precursors into vitamin D. At a dose of 25 kGy, X-rays produced 94 μg/g vitamin D3 from crystalline 7-dehydrocholesterol and 74 μg/g vitamin D2 from crystalline ergosterol. When the precursors were dissolved in oil (50 μg/ml), X-ray exposure yielded 70 ng/g vitamin D3 and 45 ng/g vitamin D2. Similar increases were also observed in mushrooms, yeast, and rodent feed. Compared with UVB irradiation, X-ray exposure produced vitamin D amounts comparable to those obtained with 20 mJ/cm2 UVB. High-dose UVB (200 mJ/cm2) yielded substantially more - 151 μg/g vitamin D3 and 188 μg/g vitamin D2 from crystalline precursors. These results demonstrate that X-ray irradiation can generate vitamin D, an unexpected and unrecognized pathway of vitamin D formation.