Why does a bearded dragon get metrobolic bone disease?

Lack of UVA & UVB light is the main cause of Metabolic Bone Disease (MBD). The lizards body synthesises vitamin A from the combination of its diet, and the UV part of the broad spectrum present in sunlight (in its natural habitat) or - in the artificial lighting in a vivarium. MBD is a debilitating illness resulting in softening of the skeletal bones - and in severe cases is FATAL !