In the absence of vitamin D, dietary calcium is not properly absorbed, resulting in hypocalcemia, leading to skeletal and dental deformities and neuromuscular symptoms, e.g. hyperexcitability. (sciencedaily.com)
Peterson ME: Hypoparathyroidism and other causes of hypocalcemia in cats, In: Kirk RW, Bonagura JD (eds): Current Veterinary Therapy XI. (animalendocrine.com)
Some types of medication can cause hypocalcemia by reducing calcium stores or making it more difficult for the body to absorb calcium. (health.com)