Vitamin D Deficiency
The vast majority of people with dark skin have this problem in northern latitudes. It can cause chronic pain. It is one of the reasons why people further from the equator tend to have fairer skin. The fairer skin allows more UVB absorbption, which activates Vitamin D in the body. Only Vitamin D3 is pre-activated. North Americans get that from dairy milk. Japanese people get it from raw fish – yet another reason to eat sushi! If people have dark skin near the north pole, it is probably because their body has adjusted to getting Vitamin D from fish rather than through other foods’ Vitamin D being activated by sunlight exposure.
As for eating meat (which I don’t do as it is), in China there can be the same chemicals in meat as what killed many pets in the US recently.
While UV rays (especially UVA) can cause skin cancer, not having enough Vitamin D apparently can increase the chances of getting other types of cancer greatly (even more so than a hefty smoking habit).