I've been thinking about vitamin D all last week after listening to Dr. Rhona patrick on joe rogan podcast( dont' hate). I haven't found and answer to this, if

I've been thinking about vitamin D all last week after listening to Dr. Rhona patrick on joe rogan podcast( dont' hate). I haven't found and answer to this, if Vitamin D is such big factor then why aren't vitamin D deficient populations in the subcontinent ( india/pakistan ..) being hit hard.