Mom, not just for this, but for any number of other things according to the MDs in these parts, is to put on shorts and a tank top and go out in the sun. The trick is that soap seems to wash the hormone off the skin before it’s absorbed, so it is recommended to only wash the areas where the glands are close to the surface to let the vit D soak in. Any number of people I know here are under orders to raise their levels and with some supplementation, this is the recommended method.
I actually spend time in the sun when I see it in Buffalo ..I garden and walk ... maybe I need more.. You know its funny, there are always unintended consequences. They tell people to wear sun block and suddenly there is an epidemic of low vit D ..DUH...