Can anyone tell me what causes a vitamin d deficiency?

Vitamin D deficiency: Normally lack of exposure to sunlight. This can be accentuated by the fact we are now also covering our bodies with more clothing and sunscreen to prevent skin cancer. In addition, lack of vit d in our diets or poor absorption of vitamin d. Foods normally don't have much vitamin d but some foods that our high in vit d include wild salmon, mackerel, eggs, liver.