Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women

Curhan GC, et al.

Published in Annals of Internal Medicine

Methodology

Prospective cohort analysis within the Nurses' Health Study using repeated semiquantitative food-frequency questionnaires and multivariate-adjusted relative risks for incident symptomatic kidney stones.

Key Findings

In 91,731 women followed for 12 years (864 incident stones), high dietary calcium intake was associated with a reduced risk of kidney stones (RR about 0.65 highest vs lowest quintile), whereas supplemental calcium use was associated with a modestly increased risk (RR about 1.20), particularly when taken apart from meals; high fluid and potassium intake were protective.

Conclusions

Calcium from food protects against kidney stones while calcium supplements taken away from meals may modestly increase risk, so dietary calcium restriction is the wrong advice for stone formers.

Limitations

Observational cohort with self-reported food-frequency data and possible residual confounding; women only, largely white nurses; timing of supplement intake relative to meals only partly captured; stone events self-reported with subset confirmation.