Vitamin D does about a million beneficial things. It is not just about secondary effects of sun exposure. Most D supplementation is done purely via pills and the benefits come without sunlight at all.
I think you may be referring to how D isn't a primary treatment for SAD. It certainly doesn't hurt to get more D in the winter for a lot of other reasons, but SAD is primarily treated via light boxes or anti-depressants.
That being said, vitamin D levels are slowly becoming the new "have you thought about losing some weight" in medicine. Being low on it isn't great, but its not the cause of the health problems people complain about.
I think you may be referring to how D isn't a primary treatment for SAD. It certainly doesn't hurt to get more D in the winter for a lot of other reasons, but SAD is primarily treated via light boxes or anti-depressants.
That being said, vitamin D levels are slowly becoming the new "have you thought about losing some weight" in medicine. Being low on it isn't great, but its not the cause of the health problems people complain about.