Table 2. Dietary calcium intake and the RR of incident kidney stones in men, 1986–2000, stratified by agea

Quintile 1Quintile 2Quintile 3Quintile 4Quintile 5P for Trendb
a For illustrative purposes, quintile medians for intake of dietary calcium were derived from responses to the 1994 dietary questionnaire. However, the period-specific quintile values were used for the 1986 to 2000 analyses. RR are for the risk for stone formation compared with the group that had the lowest intake of dietary calcium. RR, relative risk; CI, confidence interval.
b P value for interaction terms between dichotomized age and quintiles of calcium intake was 0.04. The P value for interaction between continuous age and quintiles of calcium intake was also 0.04.
c Results are adjusted for age; body mass index (six categories); use of thiazide diuretics (yes or no); volume intake (in quintiles); alcohol use (seven categories); calcium supplement use (four categories); and dietary intake of animal protein, potassium, sodium, vitamin C, and magnesium (all in quintiles).
<60 years of age
    quintile median of dietary calcium (mg/d)5036337488931194
    cases266211178188147
    person-years53,14255,08154,00752,85851,685
    age-adjusted RR (95% CI)1.00.76 (0.64–0.92)0.66 (0.54–0.80)0.71 (0.59–0.86)0.57 (0.46–0.70)<0.001
    multivariate RRc (95% CI)1.00.81 (0.68–0.98)0.72 (0.59–0.88)0.81 (0.66–0.99)0.69 (0.56–0.87)0.01
≥60 years of age
    quintile median of dietary calcium (mg/d)4986377518961218
    cases96961059591
    person-years39,22439,81741,59544,00646,287
    age-adjusted RR (95% CI)1.00.99 (0.74–1.31)1.04 (0.79–1.37)0.89 (0.67–1.18)0.81 (0.60–1.07)0.07
    multivariate RRc (95% CI)1.01.09 (0.81–1.45)1.21 (0.91–1.62)1.12 (0.83–1.52)1.20 (0.87–1.66)0.40