PTH and primary hyperparathyroidism: It is common in human to have both primary hyperparathyroidism and insufficiency of vitamin D, since primary hyperparathyroidism can lead to decreased vitamin D stores; these observations were in the same line with Berlin and Bjorkhem [77] who demonstrated that an increase in calcium intake in rats causes a reduction in the serum PTH level with a subsequent decrease in 1α-hydroxylation of 25-hydroxyvitamin D3, leading to raise level of 25-hydroxyvitamin D3 as a hypothetical result of suppression the action of the 25-hydroxylase.