Table 1.
Age-standardizeda baseline characteristics by red cell distribution width (RDW) quintile.
| RDW Quintile | ||||||
|---|---|---|---|---|---|---|
| Lowest | 2 | 3 | 4 | Highest | P valueb | |
| n | 2895 | 3289 | 3243 | 3121 | 3304 | 15852 |
| RDW, range | 10.90–12.35 | 12.50–12.65 | 12.80–13.15 | 13.20–13.75 | 13.80–30.60 | |
| RDW, median (interquartile range) | 12.10 (11.95–12.25) | 12.60 (12.50–12.65) | 12.95 (12.85–13.05) | 13.40 (13.30–13.55) | 14.35 (14.00–15.05) | |
| Age (years), mean | 39.7 | 42.0 | 45.9 | 49.0 | 54.1 | < 0.001 |
| Female sex, % | 53.2 | 50.5 | 49.0 | 52.4 | 61.2 | 0.002 |
| Race/ethnicity, % | < 0.001 | |||||
| Non-Hispanic white | 84.2 | 82.7 | 76.0 | 72.5 | 56.7 | |
| Non-Hispanic black | 5.0 | 6.1 | 9.2 | 14.0 | 29.5 | |
| Mexican American | 3.8 | 4.7 | 5.6 | 5.3 | 5.7 | |
| Other | 7.1 | 6.5 | 9.2 | 8.2 | 8.0 | |
| Highest year of education achieved, mean | 12.8 | 12.6 | 12.3 | 12.0 | 11.4 | < 0.001 |
| Graduated high school, % | 80.2 | 80.0 | 73.9 | 69.6 | 61.7 | < 0.001 |
| Pack-years of smoking, mean | 8.9 | 9.9 | 10.8 | 12.4 | 13.4 | < 0.001 |
| Active smoking, % | 18.5 | 24.6 | 30.7 | 36.5 | 37.9 | < 0.001 |
| Physical activity relative to peers, % | < 0.001 | |||||
| Less than peers | 18.4 | 19.3 | 19.6 | 24.5 | 29.3 | |
| More than peers | 39.2 | 36.4 | 36.6 | 30.2 | 27.9 | |
| Estimated glomerular filtration rate (mL/min), mean | 92.1 | 90.8 | 92.6 | 92.9 | 95.2 | < 0.001 |
| Chronic kidney disease, % | 5.2 | 4.4 | 5.4 | 6.1 | 10.6 | < 0.001 |
| Systolic blood pressure (mm Hg), mean | 123 | 123 | 123 | 125 | 126 | < 0.001 |
| Hypertension, % | 30.4 | 32.2 | 31.1 | 34.4 | 40.9 | < 0.001 |
| Hemoglobin A1c (%), mean | 5.3 | 5.4 | 5.4 | 5.5 | 5.6 | < 0.001 |
| Diabetes, % | 7.4 | 7.3 | 6.3 | 8.6 | 11.0 | 0.07 |
| Total:HDL cholesterol ratio, mean | 4.4 | 4.5 | 4.5 | 4.4 | 4.4 | 0.13 |
| Hypercholesterolemia, % | 36.3 | 35.0 | 32.0 | 32.1 | 28.6 | < 0.001 |
| Body mass index (kg/m*m), mean | 25.7 | 26.4 | 26.6 | 27.5 | 28.1 | < 0.001 |
| Obesity (BMI ≥ 30.0 kg/m*m), % | 16.5 | 21.2 | 23.3 | 27.9 | 32.3 | < 0.001 |
| Hemoglobin (g/L), mean | 143 | 144 | 143 | 142 | 132 | < 0.001 |
| Mean corpuscular volume (fL), mean | 91.0 | 90.6 | 90.3 | 89.8 | 86.9 | < 0.001 |
| Serum folate (nmol/L), mean | 17.9 | 17.1 | 15.1 | 14.0 | 13.1 | < 0.001 |
| Serum B12 (pmol/L] (n = 8,068c), mean | 360 | 356 | 354 | 360 | 359 | 0.97 |
| Serum iron (ug/dL), mean | 105 | 102 | 102 | 93 | 84 | < 0.001 |
| Cardiovascular disease, % | 4.1 | 4.6 | 5.9 | 7.7 | 9.9 | < 0.001 |
| Cancer, % | 4.3 | 4.4 | 4.0 | 3.6 | 4.3 | 0.77 |
| Lung disease, % | 12.0 | 12.0 | 13.3 | 14.5 | 14.7 | 0.01 |
a
Standardized to the United States Census 1990.
b
P value corresponds to the overall age-adjusted association between the characteristic and RDW quintile, based on linear, logistic, or multinomial logistic regression models with RDW quintiles and age as the independent variables. The comparison of age and RDW quintile does not adjust for age.
c
Vitamin B12 level was only measured in the years 1991–1994