What causes a Vitamin D deficiency?

Vitamin D deficiency results from inadequate dietary intake of preformed vitamin D, malabsorption of vitamin D, or too little exposure to sunlight. This deficiency may also occur in overcrowded urban areas in which smog limits sunlight penetration. Other conditions that can lead to Vitamin D Deficiency are habits such as smoking, diets which lack vitamin D rich foods, consumption of alchohol, stress and environmental factors.