Table 5.
Quintiles of animal protein-to-potassium ratio and risk of kidney stones
| Cohort | Quintile 1 | Quintile 2 | Quintile 3 | Quintile 4 | Quintile 5 | P Value for Trend |
|---|---|---|---|---|---|---|
| HPFS | ||||||
| Median, g/mEq | 0.46 | 0.59 | 0.70 | 0.81 | 1.01 | <0.001 |
| Range | <0.53 | 0.53–0.64 | 0.65–0.75 | 0.76–0.88 | >0.88 | <0.001 |
| Patients | 268 | 336 | 378 | 408 | 573 | 0.004 |
| Person-time | 131,584 | 132,719 | 134,206 | 135,099 | 135,879 | |
| Age-adjusted HR (95% CI) | 1.00 (reference) | 1.21 (1.03 to 1.42) | 1.30 (1.10 to 1.52) | 1.35 (1.16 to 1.59) | 1.84 (1.58 to 2.14) | |
| Model 1 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.25 (1.06 to 1.48) | 1.33 (1.13 to 1.57) | 1.36 (1.14 to 1.60) | 1.72 (1.45 to 2.04) | |
| Model 2 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.19 (0.99 to 1.44) | 1.26 (1.01 to 1.53) | 1.28 (0.98 to 1.66) | 1.63 (1.18 to 2.25) | |
| NHS I | ||||||
| Median, g/mEq | 0.46 | 0.57 | 0.67 | 0.77 | 0.94 | <0.001 |
| Range | <0.50 | 0.50–0.60 | 0.61–0.70 | 0.71–0.82 | >0.82 | 0.004 |
| Patients | 205 | 213 | 253 | 301 | 359 | <0.01 |
| Person-time | 201,541 | 201,865 | 202,107 | 202,490 | 202,439 | |
| Age-adjusted HR (95% CI) | 1.00 (reference) | 1.01 (0.84 to 1.23) | 1.21 (1.01 to 1.47) | 1.44 (1.20 to 1.74) | 1.72 (1.43 to 2.06) | |
| Model 1 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 0.98 (0.80 to 1.19) | 1.10 (0.90 to 1.35) | 1.23 (1.00 to 1.50) | 1.29 (1.04 to 1.61) | |
| Model 2 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.06 (0.85 to 1.32) | 1.26 (0.97 to 1.62) | 1.45 (1.08 to 1.95) | 1.59 (1.10 to 2.31) | |
| NHS II | ||||||
| Median, g/mEq | 0.49 | 0.64 | 0.74 | 0.86 | 1.07 | <0.001 |
| Range | <0.57 | 0.57–0.69 | 0.70–0.79 | 0.80–0.94 | >0.94 | 0.16 |
| Patients | 507 | 549 | 616 | 639 | 703 | 0.16 |
| Person-time | 283,922 | 284,365 | 285,185 | 286,649 | 288,214 | |
| Age-adjusted HR (95% CI) | 1.00 (reference) | 1.10 (0.97 to 1.24) | 1.25 (1.11 to 1.41) | 1.34 (1.19 to 1.51) | 1.53 (1.35 to 1.72) | |
| Model 1 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.04 (0.92 to 1.18) | 1.11 (0.98 to 1.26) | 1.11 (0.97 to 1.27) | 1.12 (0.97 to 1.27) | |
| Model 2 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.07 (0.93 to 1.24) | 1.18 (1.00 to 1.40) | 1.20 (0.98 to 1.46) | 1.25 (0.97 to 1.60) | |
| Pooled cohorts | ||||||
| Age-adjusted HR (95% CI) | 1.00 (reference) | 1.11 (1.02 to 1.21) | 1.26 (1.15 to 1.37) | 1.37 (1.25 to 1.49) | 1.67 (1.48 to 1.88) | <0.001 |
| Model 1 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.08 (0.94 to 1.25) | 1.18 (1.04 to 1.33) | 1.21 (1.07 to 1.37) | 1.35 (1.03 to 1.78) | 0.02 |
| Model 2 multivariate–adjusted HR (95% CI) | 1.00 (reference) | 1.10 (0.99 to 1.22) | 1.21 (1.07 to 1.36) | 1.26 (1.14 to 1.40) | 1.41 (1.18 to 1.68) | 0.004 |
Multivariate model 1 was adjusted for age, body mass index, history of diabetes, history of hypertension, use of thiazides, supplemental calcium, and intakes of fluid, calcium, sodium, fructose, oxalate, phytate, and alcohol. Multivariate model 2 was further adjusted for animal protein and potassium intake; in these models, animal protein-to-potassium ratios represent interaction terms. 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.