Just remember WYSIWYG, that window glass only permits about 5% of the UV in sunlight through and it is UV light that triggers the natural production of Vitamin D through the skin. Sitting in a window, if you are seeking all the benefits of natural sunlight, will do bugger all to increase levels of Vitamin D.

Another reason why, in earlier times, people of the very nothern extremes of our world, survived and thrived eating only fish and blubber during the long dark winter months, without falling into suicidal depressions.