The following was found at the Vitamin D Council websit:
Hypersensitivity, Not ToxicityVitamin D hypersensitivity syndromes are often mistaken for vitamin D toxicity, as they cause hypercalcemia. The most common is primary hyperparathyroidism although some cases of "primary" hyperparathyroidism are actually secondary to Vitamin D deficiency. Patients with hyperparathyroidism should only take vitamin D under the care of a knowledgeable endocrinologist. Granulomatous diseases such as sarcoidosis, granulomatous TB, and some cancers can also cause Vitamin D hypersensitivity, as the granuloma or the tumor may make excessive amounts of activated Vitamin D, thus raising serum calcium. These patients should not take vitamin D except when under the care of a knowledgeable physician.Other syndromes occur when abnormal tissue subverts the kidney's normal regulation of endocrine calcitriol production. Aberrant tissues, usually granulomatous, convert 25(OH)D into calcitriol causing high blood calcium. The most common such conditions are sarcoidosis, oat cell carcinoma of the lung, and non-Hodgkin's lymphoma but other illnesses can cause the syndrome and they can occur while the patient's 25(OH)D levels are normal, or even low. For that reason, while rare, it is advisable to seek a knowledgeable physician's care when repleting your vitamin D system, especially if you are older, have sarcoidosis, cancer, or other granulomatous diseases. In such high-risk patients, periodic monitoring of 25(OH)D levels and serum calcium will alert the physician to the need to do more tests—such as calcitriol or PTH—and take further action.It seems clear that restoring physiological serum levels of 25(OH)D will help many more patients that it will hurt. In fact, living in America today while worrying about vitamin D toxicity is like dying of thirst in the desert while worrying about drowning.
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