Impact of nutritional factors on incident kidney stone formation: A report from the WHI OS

Purpose: Increased fluid intake, and decreased dietary sodium and animal protein intake are thought to reduce the risk of kidney stones but the role of calcium intake is controversial. We evaluated the relationship between dietary factors and incident kidney stone formation. Materials and Methods: Secondary analysis was done of 78,293 women from the prospective WHI OS (Women's Health Initiative Observational Study) with no history of nephrolithiasis who completed the validated food frequency questionnaire. Multivariate logistic regression was used to determine demographic and dietary factors, and supplement use independently associated with incident kidney stones. Results: Overall 1,952 women (2.5%) reported an incident kidney stone in 573,575 person-years of followup. The risk of incident kidney stones was decreased by 5% to 28% (p = 0.01) with higher dietary calcium intake and by 13% to 31% (p = 0.002) with higher water intake after adjusting for nephrolithiasis risk factors. Conversely higher dietary sodium intake increased the risk of nephrolithiasis by 11% to 61% (p <0.001) after adjustment with the most pronounced effect in women with the highest intake. Higher body mass index independently increased the risk of incident nephrolithiasis (adjusted OR 1.19-2.01, p <0.001). Animal protein intake was not associated with nephrolithiasis on multivariate analysis. Conclusions: This study adds to the growing evidence underscoring the importance of maintaining adequate fluid and dietary calcium intake. Greater dietary calcium intake significantly decreased the risk of incident kidney stones. In contrast, excess sodium intake increased the risk of incident nephrolithiasis, especially in women with the highest intake. Animal protein intake was not independently associated with nephrolithiasis.