A condition in which the body is too low on vitamin D, a nutrient that is important for bones, nerves, muscles and the immune system.

Hypovitaminosis D can cause children's bones to become soft and weak, a condition called rickets. Hypovitaminosis D also can cause bone pain and muscle weakness in adults, a condition called osteomalacia. Low vitamin D levels can happen for reasons such as a lack of sunlight and certain health conditions.

Symptoms of severe hypovitaminosis D can include misshapen and painful bones, seizures, muscle cramps and spasms, and dental conditions in children and adults. Young children with hypovitaminosis D who also have severe rickets might have delays in development or heart muscle disease called cardiomyopathy as well.

Often hypovitaminosis D treatment involves taking daily vitamin D supplements by mouth. A healthcare professional determines how much vitamin D is needed. Some people with hypovitaminosis D also need supplements to treat low calcium and phosphate.