Intake of trace metals and the risk of incident kidney stones

PURPOSE: The association between intakes of trace metals and risk of incident stones has not been longitudinally investigated. MATERIALS AND METHODS: We performed a prospective analysis of 193,551 participants of the Health Professionals Follow-up Study (HPFS), Nurses' Health Study (NHS) I and II. During a follow-up of 3,316,580 person-years, there were 6,576 incident stones. We used multivariate regression models to identify associations between intakes of zinc, iron, copper and manganese and risk of stones. In a subset of participants with 24-hour urine collections, we examined the association between intake of trace metals and urine composition. RESULTS: After multivariate adjustment, total and dietary intakes of zinc and iron were not significantly associated with incident stones. Higher intake of manganese was associated with lower risk of stones; the pooled hazard ratio (HR) for the highest quintile of total manganese intake compared with the lowest was 0.82 (95% confidence interval [CI] 0.68, 0.98; p=0.02). Total but not dietary copper intake was marginally associated with higher risk of stones (pooled HR 1.14, 95% CI 1.02, 1.28; p=0.01). There were no statistically significant associations between total intakes of manganese and copper and urinary supersaturations. CONCLUSIONS: Intakes of zinc and iron were not associated with risk of stones. Copper intake may be associated with higher risk in some individuals. Higher total manganese intake was associated with lower risk of stones but not with traditional 24h urinary composite markers of stone risk. Further research is needed to elucidate mechanisms whereby manganese may reduce kidney stone formation.