In rheumatology, there are many patients who require calcium supplements, whether due to the need for glucocorticoids to combat osteoporosis or the effects of the disease itself. However, many patients are worried that calcium supplementation will cause kidney stones, or those who already have kidney stones are worried that they will worsen. So, is it true that calcium supplementation can cause kidney stones or aggravate kidney stones? Today we will discuss it together. The exact mechanism of urinary stones (including kidney stones) formation is not completely clear, and is mainly influenced by a combination of genetic, environmental and nutritional factors. The majority of urinary stones are calcium oxalate stones (70-80%). Studies have suggested that the formation of calcium oxalate stones depends mainly on the oxalic acid concentration. Although urinary stones are mainly formed by the combination of oxalic acid and calcium, the key to their formation does not depend on the amount of calcium intake, but mainly on the oxalic acid concentration, which plays a much greater role than calcium in the mechanism of calcium oxalate stone formation. In fact, oxalic acid has a much greater impact on urinary stone formation than you might think. Even without calcium supplementation, when oxalic acid concentrations are too high, oxalic acid can combine with calcium released from bone to form new stones or make existing stones larger. Therefore, limiting calcium intake does not reduce the formation of urinary stones. In contrast, a low-calcium diet allows excess oxalate to enter the bloodstream, which in turn is more likely to trigger the development of urinary stones. The process of proper calcium supplementation, in which excess unabsorbed calcium in the intestine combines with the oxalic acid component of the diet to form non-absorbed calcium oxalate, instead reduces the absorption of oxalic acid from intestinal sources. In turn, the occurrence of stones can be prevented. In summary, whether due to the need for glucocorticoid use to combat osteoporosis or the effects of the disease itself, appropriate and reasonable calcium supplementation when calcium is needed does not increase or exacerbate the occurrence of urinary stones. There are, however, common adverse effects of calcium supplements. Some patients may suffer from constipation, and some patients are prone to “fire” as they say in Cantonese after taking calcium tablets. For these patients, switching to chewable tablets or liquid calcium may help to avoid these reactions.