Explain the Bioavailability of Vitamin D?

The nutritional availability of vitamin D is less significant because it can be endogenously produced and retained for long periods by the tissues. Factors that affect availability are the duration of exposure to sunlight, seasonal variation, skin pigmentation, cultural practices like purdah system associated with clothing that covers the entire body and face. You might have seen small children with bow legs, who are unable to walk normally and have enlarged bone joints. These, along with many other symptoms, are associated with vitamin D deficiency.