Parathyroid Hormone, Magnesium, Vitamin D, and Mast Cell Degranulation

There's also this interesting effect of parathyroid hormone (PTH) on calcium influx into mast cells. PTH can be elevated in kidney disease and cause pathological itching and histamine release from mast cells in the skin [Szepietowski, 1998: (http://www.ncbi.nlm.nih.gov/pubmed/9585892)]. That article mentions the fact that doctors sometimes perform parathyroidectomies to treat the pruritus, and PTH is known to produce excessive calcium influx in other cell types. I know there are some articles suggesting that some of the effects of vitamin D on insulin metabolism might be due to the suppression of PTH hormone levels and the consequent suppression of excessive calcium influx into adipocytes or other cell types [McCarty and Thomas, 2003: (http://www.direct-ms.org/pdf/VitDNonAuto/MccartyPTHObesity.pdf) (http://www.ncbi.nlm.nih.gov/pubmed/14592784)]. PTH levels decrease as the 25(OH)D level increases, as an indicator of a higher vitamin D intake. An adequate vitamin D intake also increases magnesium absorption, and magnesium can have complex effects on PTH release and on the responsiveness of cells to PTH. I think the general idea is that adequate magnesium status reduces "PTH resistance," meaning that magnesium tends to increase the responsiveness of cells to PTH but to improve the feedback regulation of PTH release. But that could be another mechanism by which magnesium regulates mast cell histamine release (via "improved" regulation of PTH release or responsiveness). Moderate vitamin D intakes also increase calcium absorption, and increases in serum calcium could increase mast cell histamine release. But that's part of the idea behind my suggestion that taking more than a reasonable amount of calcium (1,000 mg or whatever reasonable amount, from food and supplements), in combination with vitamin D, could, particularly in the context of the chronically-low magnesium intakes of many people (given the removal of most magnesium from grains during processing, etc.), produce undesirable effects.