Define Deficiency and Toxicity of Vitamin D?

Infants constitute a population at-risk for vitamin D deficiency because of relatively large vitamin D needs brought about by their high rate of skeletal growth; Breast- fed infants are particularly at-risk because of the low concentrations of vitamin D in human milk. This problem is further compounded in some infants fed human milk by a restriction in exposure to ultraviolet (UV) light for seasonal, latitudinal, cultural or social reasons. Dietary absence of vitamin D or lack of UV (sunlight) exposure causes the bone disease called rickets (refer to Figure 7.10) in infant children and osteomalacia in adults.