Vitamin D deficiency can be caused by a variety of factors.
Deficiencies in vitamin D results from inadequate exposure to sunlight, inefficient production in the skin, not enough vitamin D in your diet, and health situations like gastrointestinal disorders, liver, and renal diseases.
Darker skinned people have natural sun protection due to the increase of melanin in their skin.
Being overweight or obese can place you at a higher risk for vitamin D deficiency. In 23 recent studies, obese subjects had 35% higher rates of vitamin D deficiency companies with those who maintain a healthy weight. Diet and decreased sun exposure do have some impact on this problem, but the capacity of the skin to produce vitamin D in overweight people was a definite problem.
Also, a malabsorption syndrome like celiac disease or Crohn's disease and those who have had bariatric surgery are often unable to absorb enough vitamin D.