In rheumatology, there are many patients who require calcium supplements, whether because of the need to use glucocorticoids to combat osteoporosis or because of the effects of the disease itself. However, many patients worry that calcium supplementation will cause kidney stones, or those who already have kidney stones worry that they will worsen. So, is it true that calcium supplementation can cause kidney stones or aggravate kidney stones? 1. How are stones formed? The exact mechanism of formation of urinary stones (including kidney stones) 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%). The available studies suggest 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 formation is not the amount of calcium intake, but mainly depends on the oxalic acid concentration, which plays a much greater role in the formation mechanism of calcium oxalate stones than calcium. 2. Did calcium supplementation trigger the stones? The effect of oxalic acid on the formation of urinary stones is much greater than you might think. Even without calcium supplementation, when oxalic acid concentration is too high, oxalic acid can combine with calcium released from bone to form new stones or increase the size of existing stones. 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 unabsorbed calcium oxalate, instead reduces the absorption of oxalic acid from intestinal sources. In turn, the occurrence of stones can be prevented. In summary, whether it is due to the use of glucocorticoids to prevent osteoporosis or the disease itself, proper and reasonable calcium supplementation when calcium is needed will not increase or aggravate the occurrence of urinary stones. 3. What is the best way to take calcium supplements for patients who are prone to “fire”? There are some common adverse reactions to 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 be helpful to avoid these adverse effects.