Table 3.
Baseline characteristics of the participants in the Nurses’ Health Study II (NHS II)
| Characteristic | Stone-Formers (n=436) | Nonstone-Formers (n=491) | P Value |
|---|---|---|---|
| Age at collection, yr | 49.5 (5.1) | 51.7 (4.5) | <0.001 |
| Body mass index, kg/m2 | 27.5 (6.9) | 27.2 (6.4) | 0.53 |
| Activity, mets/wk | 10.4 [3.6, 25.7] | 14.0 [5.6, 27.6] | 0.01 |
| Smoking status | |||
| Never smoked, % | 70 | 70 | 0.58 |
| Past smoker, % | 24 | 25 | |
| Current smoker, % | 6 | 5 | |
| Alcohol intake, gm/d | 0.7 [0.0, 3.6] | 1.8 [0.0, 5.7] | <0.001 |
| Estimated net endogenous acid production, mEq/d | 46.7 [39.9, 54.5] | 44.4 [37.5, 51.8] | <0.001 |
| Nondairy animal protein intake, g/d | 37.1 [27.6, 46.8] | 35.4 [27.7, 44.8] | 0.39 |
| Dairy protein intake, g/d | 15.5 [10.4, 21.9] | 14.7 [9.5, 20.4] | 0.07 |
| Vegetable protein intake, g/d | 24.7 [21.3, 28.9] | 25.7 [21.8, 30.1] | 0.02 |
| Potassium intake, mg/d | 2961 [2587, 3339] | 3094 [2700, 3510] | <0.001 |
| Total fat intake, g/d | 65.2 [57.3, 76.0] | 63.7 [56.6, 72.9] | 0.05 |
| Carbohydrate intake, g/d | 227 [200, 251] | 231 [202, 250] | 0.44 |
| Dietary vitamin C intake, mg/d | 105 [73, 139] | 116 [82, 154] | 0.005 |
| Total vitamin C intake, mg/d | 160 [103, 270] | 183 [116, 348] | <0.001 |
| History of hypertension, % | 30 | 29 | 0.74 |
| History of diabetes mellitus, % | 6 | 5 | 0.39 |
| History of gout, % | 2 | 1 | 0.16 |
| Thiazide use, % | 9 | 11 | 0.35 |
| Urinary creatinine, mg/d | 1238 (246) | 1251 (232) | 0.41 |
| Urinary sodium, mEq/24 h | 152 (52) | 150 (49) | 0.57 |
| Urinary citrate, mg/d | 732 (300) | 807 (283) | <0.001 |
Values are means (SD), median [interquartile range], or percentages. Percentages may not add up to 100% because of individuals with missing values.