What causes a vit d deficiency?

Intake deficiency: Hi. Humans can make their own vitamin D with adequate sunlight exposure, which VERY few people in our society get (we're indoors all day working, we use sun block to prevent skin cancer). We get most of our vitamin D from diet (milk) or supplements. Vitamin D supplements are best taken with a meal (fat soluble vitamin-needs bile excretion into the intestine for absorption. Malabsorption conditions

Vitamin D deficiency: is now recognized as a pandemic. The major cause of vitamin D deficiency is the lack of appreciation that sun exposure in moderation is the major source of vitamin D for most humans. Very few foods naturally contain vitamin D, and foods that are fortified with vitamin D are often inadequate to satisfy either a child's or an adult's vitamin D requirement.