Table 1. Characteristics of Patients With Rheumatoid Arthritis by Serum Folate Tertile From the Third National Health and Nutrition Survey, 1988-1994.
| Characteristic | No. (%) | P Valueb | |||
|---|---|---|---|---|---|
| Total (N = 683) | Folate Tertile 1 (n = 239)a | Folate Tertile 2 (n = 234)a | Folate Tertile 3 (n = 210)a | ||
| Age, mean (SE), y | 55.86 (1.02) | 52.33 (1.36) | 55.62 (1.99) | 59.42 (1.68) | .005 |
| Men | 225 (30.2) | 80 (36.8) | 82 (31.9) | 63 (22.4) | .17 |
| White | 478 (87.0) | 140 (80.3) | 167 (88.0) | 171 (92.3) | <.001 |
| Body mass index, mean (SE)c | 27.88 (0.27) | 28.92 (0.53) | 27.32 (0.61) | 27.45 (0.59) | .14 |
| C-reactive protein, mean (SE), mg/dLd | 1.23 (0.09) | 1.32 (0.17) | 1.13 (0.12) | 1.21 (0.16) | .62 |
| Serum homocysteine, mean (SE), mg/Le | 1.34 (0.06) | 1.75 (0.09) | 1.33 (0.07) | 1.08 (0.06) | <.001 |
| Current smoker | 357 (58.1) | 142 (68.0) | 113 (53.2) | 102 (53.4) | .04 |
| DMARD use | 27 (4.5) | 7 (3.5) | 9 (1.9) | 11 (8.0) | .03 |
| Steroid use | 37 (6.0) | 15 (7.1) | 9 (3.1) | 13 (7.9) | .25 |
| NSAID use | 171 (23.9) | 57 (27.9) | 61 (21.0) | 53 (23.0) | .25 |
| Folic acid supplement use | 179 (32.2) | 29 (11.7) | 33 (17.8) | 117 (65.3) | <.001 |
| Cardiovascular disease | 131 (14.8) | 43 (14.8) | 43 (12.5) | 45 (17.0) | .63 |
| Diabetes | 107 (12.5) | 24 (9.8) | 37 (11.2) | 46 (15.9) | .23 |
| Hypertension | 301 (37.3) | 100 (39.1) | 101 (38.7) | 100 (34.3) | .65 |
Abbreviations: DMARD, disease-modifying antirheumatic drug; NSAID, nonsteroidal anti-inflammatory drug.
SI conversion factors: To convert C-reactive protein to nanomoles per liter, multiply by 9.524; homocysteine to micromoles per liter, multiply by 7.397; folate to nanomoles per liter, multiply by 2.266.
Tertile 1 defined as patients with folate levels less than 4.3 ng/mL; tertile 2, 4.3 to 8.2 ng/mL; and tertile 3, greater than 8.2 ng/mL.
P value represents National Health and Nutrition Examination Survey weight-adjusted analysis of variance for continuous variables and χ2 test for categorical variables.
Body mass index was calculated as weight in kilograms divided by height in meters squared.
Mean values for 313 patients in detectable range for laboratory assay.
Mean values for 355 patients with nonmissing data for serum homocysteine.