Because of high correlations between dairy intake and total dietary calcium, previously reported associations between lower calcium intake and increased kidney stone risk represent de facto associations between milk products and risk. We examined associations between dietary calcium from nondairy and dairy sources, and symptomatic nephrolithiasis.
We performed prospective studies in the Health Professionals Follow-up Study (HPFS) in 30,762 men, and in the Nurses' Health Study (NHS) I and II in 94,164 and 101,701 women, respectively. We excluded men 60 years old or older because we previously reported inverse associations between calcium intake and risk only in men younger than 60 years. Food frequency questionnaires were used to assess calcium intake every 4 years. We used Cox proportional hazards regression to adjust for age, body mass index, supplemental calcium, diet and other factors.
We documented 5,270 incident kidney stones during the combined 56 years of followup. In participants in the highest vs the lowest quintile of nondairy dietary calcium the multivariate relative risk of kidney stones was 0.71 (95% CI 0.56-0.92, p for trend 0.007) in HPFS, 0.82 (95% CI 0.69-0.98, p trend 0.08) in NHS I and 0.74 (95% CI 0.63-0.87, p trend 0.002) in NHS II. When comparing the highest to the lowest quintile of dairy calcium, the multivariate relative risk was 0.77 (95% CI 0.63-0.95, p trend 0.01) for HPFS, 0.83 (95% CI 0.69-0.99, p trend 0.05) for NHS I and 0.76 (95% CI 0.65-0.88, p trend 0.001) for NHS II.
Higher dietary calcium from nondairy or dairy sources is independently associated with a lower kidney stone risk.