Table 4.

Total spinach intake and the relative risk for incident kidney stones in men (HPFS), older women (NHS I), and younger women (NHS II)

ParameterSpinach Servings
<1/mo1 to 7/mo≥8/mo
HPFS
    cases541936150
    person-years174,589307,68053,214
    age-adjusted RR (95% CI)1.00.95 (0.86 to 1.06)0.89 (0.75 to 1.07)
    multivariate RR (95% CI)a1.01.11 (0.99 to 1.24)1.30 (1.08 to 1.58)
NHS I
    cases468807139
    person-years411,253753,777125,316
    age-adjusted RR (95% CI)1.00.92 (0.82 to 1.03)0.95 (0.78 to 1.14)
    multivariate RR (95% CI)a1.01.09 (0.97 to 1.23)1.34 (1.10 to 1.64)
NHS II
    cases684766114
    person-years328,525445,46473,598
    age-adjusted RR (95% CI)1.00.84 (0.76 to 0.93)0.76 (0.62 to 0.93)
    multivariate RR (95% CI)a1.00.96 (0.87 to 1.07)1.00 (0.81 to 1.24)
  • a Results adjusted for age; BMI (six categories); use of thiazide diuretics (yes or no); fluid intake (in quintiles); alcohol use (seven categories); calcium supplement use (four categories); and dietary intake of animal protein, calcium, potassium, sodium, phytate, vitamin C, and magnesium (all in quintiles).