Exactly. We are evolved to have dark skin and so to make enough Vitamin D for somebody living in Central Africa. When humans moved North, those with darker skin couldn't make enough Vitamin D, so they were selected out. There was selective pressure to have lighter skin, which increased Vitamin D production. Now we have lots of mobility which leads to darker-skinned people living in areas with less sun, and we have clothes, cars, indoor occupations, and skin-cancer warnings. So there are wide-spread deficiencies in places you would never suspect. For example Muslim women in the sunny Middle East have a cultural requirement for extremely modest clothing, which makes them very deficient. In some cultures, lighter skin is associated with class, so people stay out of the sun as much as possible.

Central African tribesmen and lifeguards in Hawaii both top out at about 70 ng/ml. Some of the more liberal medical establishment says 30 ng/ml is fine. Well, you certainly won't get rickets at 30. USRDA is enough to get you to 6 ng/ml with no sun-made Vitamin D. It still assumes we all work on farms, or ride horses all day long.

Educating anyone benefits everyone.