“...you get a sufficient amount of Vitamin C in just a few minutes each day (like walking to your car or across the parking lot).”
If it were that easy there shouldn’t be widespread deficiencies.
There really aren’t widespread deficiencies, at least not in this country. There aren’t too many Americans walking around with rickets or osteomalacia. And in this country at least, milk is fortified with Vit D. A large problem with that is so many people drink soda instead of milk. It’s nothing for people to take in a liter or two of soda a day, even for teenagers.