Calcium (oral salts: carbonate, citrate, lactate, gluconate) × Cholecalciferol

Here the combination is intended: vitamin D increases intestinal calcium absorption, which is why the two are prescribed together in osteoporosis. The problem comes from excess, not deficit. With sustained high doses of both, the enhanced absorption can lead to hypercalcaemia, particularly in someone already on a thiazide diuretic or with reduced renal function.

Intense thirst, passing large volumes of urine, constipation, nausea, weakness, confusion. On labs, high serum calcium and, over time, kidney stones and vascular calcification.

The combination at guideline doses is correct and should not be avoided. What needs watching is the unintended sum: supplement calcium plus a bone complex plus dietary calcium, with vitamin D from another bottle. Read labels to avoid duplication, and on long-term treatment monitor serum calcium and renal function. Self-directed monthly megadoses of vitamin D add nothing and increase this risk.