Table 1.

Characteristics of study participants by cohort

HPFS (n = 1037)NHS I (n = 1246)NHS II (n = 1085)
Demographic and dietary factors
    age (yr)63.4 (58.8 to 69.3)66.1 (61.3 to 71.3)49.8 (45.3 to 53.8)
    BMI (kg/m2)25.8 (23.7 to 28.0)26.0 (22.9 to 29.8)25.3 (22.5 to 30.7)
    history of kidney stones63.0%69.1%63.3%
    history of hypertension35.3%48.8%22.0%
    thiazide use8.8%16.3%14.9%
    history of diabetes5.7%10.0%4.5%
    history of gout7.0%3.7%1.3%
    family history of kidney stones18.1%N/A25.7%
    calcium supplement use48.1%69.0%63.3%
    total calcium intake (mg/d)890 (701 to 1180)1196 (759 to 1684)1239 (821 to 1731)
    dietary calcium intake (mg/d) (non-supplement users)750 (615 to 944)655 (524 to 821)787 (632 to 1006)
    caffeine (mg/d)101 (30 to 228)106 (22 to 229)107 (30 to 225)
Urinary factors
    urinary magnesium (mg/d)118 (94 to 147)95 (74 to 122)94 (74 to 121)
    urinary sodium (mEq/d)173 (134 to 224)132 (99 to 172)144 (109 to 182)
    urinary sulfate (mmol/d)22 (17 to 28)16 (12 to 20)16 (13 to 20)
    urinary citrate (mg/d)666 (480 to 889)613 (427 to 817)724 (544 to 910)
    urinary phosphorus (mg/d)1032 (852 to 1249)732 (593 to 904)808 (649 to 999)
    urinary volume (L/d)1.6 (1.2 to 2.1)1.7 (1.3 to 2.2)1.6 (1.2 to 2.2)
    urinary potassium (mEq/d)73 (58 to 91)58 (45 to 73)53 (42 to 66)
    urinary creatinine (mg/d)1627 (1379 to 1896)1030 (886 to 1185)1171 (1018 to 1359)
    urinary calcium (mg/d)182 (122 to 255)182 (117 to 252)192 (141 to 259)
  • Note: Data are presented as median (25th to 75th percentile) unless otherwise indicated. HPFS, Health Professionals Follow-up Study; NHS, Nurses' Health Study; BMI, body mass index.