"You mentioned in your speech, that vitamin D in sufficient amount in a half hour sunshine with a walk with rolled up sleeves of the body can be produced. This must be out there or may have same effect also through glass, such as in a winter garden be achieved?"
For the vitamin production D – we need people of UVB radiation. She is well filtered by glass.
Depending on how high the Sun is, giving it more UVB radiation (which is brown) or more UVA radiation (the skin aging that is) into the light. At lunchtime, the ratio is preferred (little UVA, much UVB). There, already 20 minutes for the healthy dose range – depending on the skin type and UV-index – then in the summer. A good tool is "D minder", an app that calculates what enough and what is too much sun, depending on the skin type, and then informs you. http://dminder.ontometrics.com/
To produce vitamin D in the winter sun is people in our latitudes very rare. It is approx. In the body memory available for 90 days. That's enough almost for a whole winter.
A Conservatory is a super thing, anyway to get the sufficient amount of light in the winter to encourage other hormones (particularly serotonin).
Best regards, Miriam