PTH and vitamin D deficiency: In patients with vitamin D deficiency, even minimal damage to the parathyroid glands caused by surgical manipulation may temporarily reduce PTH secretion and cause hypocalcemia, because these patients’ calcium regulation presents greater sensitivity to circulating serum PTH levels than that of individuals with normal levels of vitamin D. The role of vitamin D deficiency in causing parathyroid enlargement42 supports the idea that increased parathyroid gland activity compensates for low vitamin levels, thus making these patients more susceptible to hypocalcemia after thyroidectomy.