Table 1.
Baseline characteristics of participants according to the FT3/FT4 ratio in NHANES III (2007-2012).
| Characteristic | Total | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | P value |
|---|---|---|---|---|---|---|
| (< 3.589) | (3.590-4.064) | (4.065-4.570) | (≥ 4.571) | |||
| Participants, No. | 8018 | 2004 | 2003 | 1887 | 2124 | |
| Age, mean (SD), y | 48.93 (17.62) | 55.95 (18.21) | 49.40 (17.65) | 46.06 (16.65) | 44.41 (15.63) | < 0.001 |
| Sex (men) | 3889 (48.50) | 1110 (55.39) | 1037 (51.77) | 865 (45.84) | 877 (41.29) | < 0.001 |
| FT4, mean (SD), ng/dl | 0.79 (0.16) | 0.93 (0.18) | 0.81 (0.08) | 0.76 (0.12) | 0.67 (0.11) | < 0.001 |
| FT3, mean (SD), ng/dl | 3.18 (0.56) | 2.95 (0.41) | 3.11 (0.31) | 3.26 (0.52) | 3.41 (0.75) | < 0.001 |
| TSH, mean (SD), µIU/ml | 1.55 (1.05-2.31) |
1.50 (1.03-2.19) |
1.55 (1.05-2.27) |
1.57 (1.06-2.31) |
1.60 (1.06-2.42) |
< 0.001 |
| Race/ethnicity | < 0.001 | |||||
| Mexican American | 1332 (16.61) | 264 (13.17) | 315 (15.73) | 336 (17.81) | 417 (19.63) | |
| Non-Hispanic white | 1494 (18.63) | 426 (21.26) | 374 (18.67) | 317 (16.80) | 377 (17.75) | |
| Non-Hispanic black | 3554 (44.33) | 903 (45.06) | 878 (43.83) | 873 (46.26) | 900 (42.37) | |
| Other | 1638 (20.43) | 411 (20.51) | 436 (21.77) | 361 (19.13) | 430 (20.25) | |
| Education | < 0.001 | |||||
| < High school | 2351 (29.35) | 584 (29.22) | 542 (27.07) | 568 (30.12) | 657 (30.96) | |
| High school/GED | 1872 (23.37) | 407 (20.36) | 455 (22.73) | 451 (23.91) | 559 (26.34) | |
| > High school | 3786 (47.27) | 1008 (50.43) | 1005 (50.20) | 867 (45.97) | 906 (42.70) | |
| Marital Status | < 0.001 | |||||
| Married/unmarried couple | 4824 (60.18) | 1176 (58.71) | 1226 (61.21) | 1127 (59.76) | 1295 (60.97) | |
| Divorced/widowed/separated | 1743 (21.74) | 530 (26.46) | 438 (21.87) | 392 (20.79) | 383 (18.03) | |
| Never married | 1449 (18.08) | 297 (14.83) | 339 (16.93) | 367 (19.46) | 446 (21.00) | |
| Alcohol drinking | 5333 (72.64) | 1224 (67.14) | 1330 (72.28) | 1289 (74.60) | 1490 (76.37) | < 0.001 |
| Cotinine, ng/mL | < 0.001 | |||||
| > 10 | 2092 (26.10) | 406 (20.28) | 493 (24.61) | 549 (29.09) | 644 (30.32) | |
| LOD-10 | 4309 (53.76) | 1128 (56.34) | 1079 (53.87) | 960 (50.87) | 1142 (53.77) | |
| < LOD | 1615 (20.15) | 468 (23.38) | 431 (21.52) | 378 (20.03) | 338 (15.91) | |
| BMI, kg/m2 | < 0.001 | |||||
| < 25 | 2361 (29.85) | 673 (34.27) | 593 (29.83) | 556 (29.88) | 539 (25.70) | |
| 25-29.9 | 2713 (34.30) | 633 (32.23) | 698 (35.11) | 632 (33.96) | 750 (35.77) | |
| ≥ 30 | 2836 (35.85) | 658 (33.50) | 697 (35.06) | 673 (36.16) | 808 (38.53) | |
| Liver impairment | 276 (3.45) | 67 (3.35) | 76 (3.80) | 61 (3.24) | 72 (3.40) | 0.787 |
| Renal impairment | 3376 (42.13) | 1131 (56.44) | 883 (44.11) | 682 (36.18) | 680 (32.05) | < 0.001 |
| Cancer | 705 (8.81) | 239 (11.94) | 202 (10.10) | 152 (8.06) | 112 (5.28) | < 0.001 |
| Diabetic | 1475 (18.40) | 525 (26.20) | 356 (17.77) | 299 (15.85) | 295 (13.89) | < 0.001 |
| Hypertension | 3253 (40.58) | 1016 (50.72) | 798 (39.84) | 682 (36.14) | 757 (35.64) | < 0.001 |
| Hypercholesterolemia | 3086 (38.49) | 838 (41.84) | 777 (38.79) | 675 (35.77) | 796 (37.48) | < 0.001 |
| CVD | 789 (9.84) | 334 (16.67) | 175 (8.74) | 141 (7.47) | 139 (6.54) | < 0.001 |
| CHF | 219 (2.74) | 114 (5.72) | 45 (2.25) | 32 (1.70) | 28 (1.32) | < 0.001 |
| CHD | 289 (3.62) | 128 (6.42) | 69 (3.45) | 54 (2.87) | 38 (1.80) | < 0.001 |
| Angina | 178 (2.23) | 69 (3.46) | 46 (2.30) | 38 (2.02) | 25 (1.18) | < 0.001 |
| MI | 316 (3.95) | 126 (6.30) | 69 (3.45) | 68 (3.61) | 53 (2.50) | < 0.001 |
| Stroke | 278 (3.47) | 123 (6.15) | 64 (3.20) | 44 (2.34) | 47 (2.22) | < 0.001 |
| Family history of CVD | 991 (12.71) | 274 (14.16) | 240 (12.33) | 207 (11.24) | 270 (13.01) | 0.053 |
FT3, free triiodothyronine; FT4, free thyroxine; TSH, thyroid-stimulating hormone; GED, general education development; LOD, limit of detection; BMI, body mass index; CVD, cardiovascular diseases; CHF, congestive heart failure; CHD, coronary heart disease; MI, myocardial infarction.