Table 2.

Quintiles of dairy protein intake and risk of kidney stones

CohortQuintile 1Quintile 2Quintile 3Quintile 4Quintile 5P Value for Trend
HPFS
 Median, g/d6.110.213.818.528.0<0.001
 Range<8.48.4–12.012.1–15.916.0–22.2>22.20.59
 Patients426427361419330
 Person-time129,932132,983134,714135,399136,458
 Age-adjusted HR (95% CI)1.00 (reference)0.97 (0.85 to 1.11)0.81 (0.71 to 0.94)0.94 (0.82 to 1.08)0.76 (0.66 to 0.88)
 Multivariate-adjusted HR (95% CI)1.00 (reference)0.97 (0.84 to 1.11)0.83 (0.71 to 0.96)1.00 (0.87 to 1.16)0.93 (0.78 to 1.10)
NHS I
 Median, g/d6.510.313.617.825.40.003
 Range<8.58.5–11.912.0–15.515.6–20.9>20.90.89
 Patients282281275275218
 Person-time195,814202,303203,431205,077203,817
 Age-adjusted HR (95% CI)1.00 (reference)0.96 (0.81 to 1.13)0.93 (0.79 to 1.10)0.93 (0.78 to 1.09)0.76 (0.63 to 0.90)
 Multivariate-adjusted HR (95% CI)1.00 (reference)0.99 (0.84 to 1.17)1.01 (0.85 to 1.20)1.06 (0.89 to 1.27)0.95 (0.76 to 1.17)
NHS II
 Median, g/d8.413.017.022.230.7<0.001
 Range<10.910.9–15.015.1–19.319.4–25.7>25.7<0.01
 Patients684655597569509
 Person-time279,594284,238286,507288,062289,934
 Age-adjusted HR (95% CI)1.00 (reference)0.93 (0.83 to 1.03)0.84 (0.75 to 0.93)0.79 (0.70 to 0.88)0.70 (0.62 to 0.78)
 Multivariate-adjusted HR (95% CI)1.00 (reference)0.97 (0.87 to 1.08)0.90 (0.80 to 1.01)0.88 (0.78 to 0.99)0.84 (0.73 to 0.96)
Pooled cohorts
 Age-adjusted HR (95% CI)1.00 (reference)0.95 (0.88 to 1.02)0.85 (0.78 to 0.92)0.87 (0.77 to 0.99)0.73 (0.67 to 0.79)<0.001
 Multivariate-adjusted HR (95% CI)1.00 (reference)0.97 (0.90 to 1.05)0.90 (0.82 to 1.00)0.97 (0.86 to 1.08)0.89 (0.81 to 0.98)0.06
  • Multivariate models were adjusted for age, body mass index, history of diabetes, history of hypertension, use of thiazides, supplemental calcium, and intakes of fluid, sodium, potassium, fructose, oxalate, phytate, alcohol, and all other sources of protein. Medians refer to the first time period; however, dietary variables were updated over the course of the study. HPFS, Health Professionals Follow-Up Study; HR, hazard ratio; 95% CI, 95% confidence interval; NHS I, Nurses’ Health Study I; NHS II, Nurses’ Health Study II.