Which of the following cause low serum calcium?

Vitamin D is a group of fat-soluble secosteroids responsible for enhancing intestinal absorption of calcium and phosphate. Calcitriol circulates as a hormone in the blood, regulating the concentration of calcium and phosphate in the bloodstream and promoting the healthy growth and remodeling of boneRef: Ganong&;s review of medical physiology; 24th edition; page no:-379