Baseline characteristics of controls by quartile of plasma bicarbonate
| Characteristic | Quartile of plasma bicarbonate; median (IQR)*† | p value‡ | |||
|---|---|---|---|---|---|
| Quartile 1 (< 20.6 mmol/L) n = 189 | Quartile 2 (20.6–22.3 mmol/L) n = 176 | Quartile 3 (22.4–23.9 mmol/L) n = 183 | Quartile 4 (> 23.9 mmol/L) n = 182 | ||
| Age at blood draw, yr, mean ± SD | 54.0 ± 5.0 | 55.8 ± 5.1 | 56.4 ± 5.1 | 56.6 ± 4.9 | < 0.01 |
| White, % | 99 | 97 | 99 | 99 | 0.9 |
| Body mass index, kg/m2 | 26.6 (22.7–30.9) | 25.6 (22.5–31.9) | 25.8 (23.5–30.7) | 24.9 (22.9–29.3) | 0.2 |
| Smoking status, % | 0.01 | ||||
| Never smoked | 48 | 49 | 45 | 56 | |
| Past smoker | 33 | 42 | 48 | 34 | |
| Current smoker | 19 | 9 | 7 | 10 | |
| Activity, METs/wk§ | 11.4 (4.6–23.3) | 11.8 (5.9–21.4) | 10.9 (4.2–22.0) | 15.0 (6.3–26.3) | 0.04 |
| Alcohol intake, g/d | 2.2 (0.5–7.8) | 2.8 (0.5–7.6) | 1.7 (0.2–7.5) | 3.2 (0.4–9.4) | 0.3 |
| Animal protein intake, g/d | 56.5 (49.0–62.2) | 55.6 (49.5–62.8) | 55.8 (48.4–63.4) | 57.7 (49.6–64.1) | 0.7 |
| Potassium intake, mg/d | 2857 (2519–3187) | 2842 (2549–3164) | 2866 (2584–3250) | 2907 (2610–3222) | 0.6 |
| Total calcium intake, mg/d | 856 (679–1098) | 843 (679–1080) | 877 (638–1136) | 890 (745–1121) | 0.3 |
| Magnesium intake, mg/d | 287 (257–320) | 290 (257–333) | 288 (256–334) | 295 (258–329) | 0.9 |
| Cereal fibre intake, g/d | 3.7 (2.9–5.0) | 3.9 (2.9–4.7) | 3.8 (2.9–4.8) | 3.5 (2.9–4.8) | 0.9 |
| Trans fat intake, g/d | 3.3 (2.8–3.8) | 3.2 (2.7–3.8) | 3.2 (2.7–3.9) | 3.3 (2.7–3.8) | 0.8 |
| Glycemic index | 52.3 (50.4–54.7) | 52.2 (50.4–54.2) | 52.3 (50.2–54.5) | 51.9 (49.9–53.8) | 0.4 |
| Diabetes diet score¶ | 12.0 (10.0–14.0) | 12.0 (10.0–14.0) | 12.0 (10.0–14.0) | 12.0 (10.0–14.0) | 0.9 |
| COPD, % | 14 | 15 | 11 | 8 | 0.2 |
| Hypertension, % | 22 | 28 | 34 | 36 | 0.04 |
| Hypercholesterolemia, % | 39 | 35 | 42 | 34 | 0.4 |
| Thiazide use, % | 6 | 18 | 18 | 25 | < 0.01 |
| Family history of diabetes, % | 24 | 27 | 28 | 23 | 0.2 |
| Use of postmenopausal hormones, % | < 0.01 | ||||
| Premenopausal | 33 | 25 | 19 | 13 | |
| Past use | 9 | 11 | 10 | 15 | |
| Current use | 35 | 38 | 36 | 38 | |
| Never used | 24 | 25 | 35 | 34 | |
| Creatinine, mg/dL | 0.64 (0.58–0.72) | 0.69 (0.62–0.76) | 0.71 (0.64–0.81) | 0.72 (0.64–0.81) | < 0.01 |
| Estimated GFR, mL/min/1.73m2 | 101.6 (93.8–106.7) | 95.6 (87.9–101.8) | 94.6 (83.1–101.1) | 92.5 (81.8–99.1) | < 0.01 |
| C-reactive protein, mg/dL | 0.14 (0.06–0.36) | 0.15 (0.06–0.35) | 0.17 (0.07–0.32) | 0.15 (0.09–0.32) | 0.8 |
| Hemoglobin A1C, % | 5.5 (5.4–5.8) | 5.6 (5.4–5.7) | 5.6 (5.5–5.8) | 5.6 (5.5–5.8) | 0.2 |
| Insulin, μU/mL | 8.1 (4.9–12.0) | 8.6 (4.4–12.8) | 9.7 (6.5–12.8) | 9.3 (5.0–13.2) | 0.5 |
| Plasma bicarbonate, mmol/L | 19.5 (18.3–19.9) | 21.4 (20.9–21.7) | 23.1 (22.7–23.6) | 25.3 (24.4–26.4) | < 0.01 |
Note: COPD = chronic obstructive pulmonary disease, GFR = glomerular filtration rate, IQR = interquartile range, METs = metabolic equivalents, SD = standard deviation.
↵* Unless otherwise stated.
↵† Percentages have been adjusted for age.
↵‡ p values are from analysis of variance for characteristics reported as means, Kruskal–Wallis test for those reported as medians, and χ2 test for those reported as percentages.
↵§ Physical activity reported on questionnaires was converted into METs using an established coding system. (15)
↵¶ Diabetes scores ranged from 4 to 20, with higher scores associated with a reduced risk of type 2 diabetes mellitus.