Administration of calcium and vitamin D supplementation in kidney stone formers

Nephrolithiasis is a common medical issue worldwide and it has an overall prevalence of 7% in women and 10.5% in men (1). It mainly affects active working age population and has high socioeconomic burden (2). Calcium comprises about 80%-90% of the kidney stones components as calcium oxalate and calcium phosphate, so that applying measures for reducing urine calcium excretion have increasingly been used (3). Calcium is absorbed by both active calcitriol-dependent and passive mechanisms in small bowel depending on the amount of daily consumption, and it ranges between 10% to 70% (4,5). It has been shown that kidney stone formers have higher fractional absorption of calcium in intestine leading to greater urinary calcium excretion (6,7). Multiple large studies have shown that calcium intake has a protective role against kidney stone formation by decreasing absorption of intestinal oxalate and subsequent decline in urine oxalate (8-10). Furthermore, Restriction of calcium intake not only would raise risk of oxalate absorption, it also has detrimental effect on bone mineral density which has already been lost in kidney stone formers (11). Therefore, moderate calcium intake of 800-1200 mg daily, mainly by calcium-rich diet or as supplementation taking with diet, is advocated for stone formers (12). It has been demonstrated that intake of calcium supplements both with and without meal increases urine calcium, but because of binding of dietary oxalate with calcium when it is taken with meal, the amount of intestinal oxalate absorption and its urine secretion declines and the rate of stone formation would not increase (13). Of note, apart from calcium intake in high amounts, several other dietary habits including low fluid intake, small intake of fruits and vegetable, large sodium intake, excessive consumption of diet rich in oxalate, and high meat intake are involved in stone formation (14). Therefore, patients who are taking calcium and vitamin D supplements should be advised to consider the foregoing predisposing factors of stone formation. Also, as several systemic diseases such as diabetes, obesity and hypertension are linked with stone disease (15,16), approaches for managing these conditions Implication for health policy/practice/research/medical education Taking recommended doses of supplemental calcium and vitamin D among nephrolithiasis patients have no significant consequence on kidney stone formation.