As a preventative turkzilla,
Vitamin D3 in sufficient quantities is difficult if not impossible to get from food sources alone, and therefore daily sunbathing is necessary during the summer months, but in the Winter, only supplemental sources have sufficient quantities.
D3 can also be used as a treatment for influenza of up to 20,000ius per day and more with no toxicity, as this is equivalent to a half to one hour full body sun-exposure.