Generation of previtamin D3 from tachysterol3: a novel approach for producing vitamin D3 in the winter
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Solar ultraviolet-B (UVB) radiation is capable of converting 7-dehydrocholesterol (7-DHC) to previtamin D3 (preD3), which undergoes thermal isomerization to produce vitamin D3. Further ultraviolet irradiation of preD3 will produce other photoproducts, including lumisterol3, tachysterol3, and 7-DHC. Continued exposure to UVB results in a photoequilibrium of these photoproducts. During the winter months, people living at latitudes greater than 32° north or south are incapable of converting cutaneous 7-DHC to preD3. Because an increased zenith angle creates a longer path-length for UVB radiation to traverse through the atmosphere, ozone can absorb a much greater proportion of this radiation. Given the absorption spectrum of tachysterol3 which absorbs UV radiation up to 340nm, it was hypothesized that winter sunlight which contains UV radiation between 315nm and 340nm would be able to convert tachysterol3 to preD3. Each hour between sunrise and sunset, ampules containing 50g/mL tachysterol3, lumisterol3, and 7-DHC in 100% ethanol were exposed to solar radiation. These samples were chromatographed on a normal phase chromatographic column. Results revealed that tachysterol3 was efficiently converted to preD3 from sunrise to sunset, whereas as 7-DHC and lumisterol3 were not. Exposure of tachysterol3 to sunlight throughout the day revealed that tachysterol3 began converting to preD3 at sunrise at 8am and the peak conversion occurred between 10:00 and 13:00. PreD3 was generated from tachysterol3 until sunset. No preD3 was observed when 7-DHC or lumisterol3 were exposed at the same time. From this data, it is feasible to use tachysterol3 to produce preD3 in a topical preparation during winter.