Table 1.
Characteristics of study participants
| Variables | Euthyroid | Mild SCH | Severe SCH | OH | P for trend | Euthyroid | Mild SCH | Severe SCH | OH | P for trend |
| Men (N=38 182) | Women (N=40 288) | |||||||||
| Number of participants | 31 816 (83.3) | 3964 (10.4) | 274 (0.7) | 226 (0.6) | – | 28 530 (70.8) | 6399 (15.9) | 472 (1.2) | 715 (1.8) | – |
| Mean age, years | 42.4 (0.1) | 46.0 (0.3) | 53.5 (1.0) | 54.2 (1.1) | <0.001 | 42.7 (0.1) | 46.3 (0.2) | 49.6 (0.7) | 49.7 (0.5) | <0.001 |
| Education level | ||||||||||
| Primary school and lower | 4965 (15.7) | 828 (21.0) | 92 (33.7) | 81 (36.2) | <0.001 | 7104 (25.0) | 1937 (30.4) | 180 (38.2) | 298 (41.8) | <0.001 |
| Middle and high school | 15 786 (49.8) | 1891 (47.9) | 118 (43.2) | 99 (44.2) | – | 12 316 (43.3) | 2693 (42.3) | 191 (40.6) | 297 (41.7) | – |
| College and higher | 10 964 (34.6) | 1228 (31.1) | 63 (23.1) | 44 (19.6) | – | 9012 (31.7) | 1740 (27.3) | 100 (21.2) | 118 (16.5) | – |
| Iodine intake | ||||||||||
| Adequate iodine intake | 16 145 (50.7) | 1734 (43.7) | 100 (36.5) | 108 (47.8) | <0.001 | 14 747 (51.7) | 2804 (43.8) | 178 (37.7) | 367 (51.3) | <0.001 |
| More than adequate iodine intake | 11 684 (36.7) | 1521 (38.4) | 109 (39.8) | 94 (41.6) | – | 10 417 (36.5) | 2511 (39.2) | 204 (43.2) | 272 (38.0) | – |
| Excessive iodine intake | 3987 (12.5) | 709 (17.9) | 65 (23.7) | 24 (10.6) | – | 3366 (11.8) | 1084 (16.9) | 90 (19.1) | 76 (10.6) | – |
| Percentage consumption of iodised salt | 30 483 (95.8) | 3807 (96.0) | 264 (96.4) | 217 (96.0) | 0.05 | 27 169 (95.2) | 6148 (96.1) | 451 (95.6) | 677 (94.7) | 0.03 |
| Coastal residents | 9369 (29.4) | 850 (21.4) | 43 (15.7) | 52 (23.0) | <0.001 | 8229 (28.8) | 1373 (21.5) | 93 (19.7) | 153 (21.4) | <0.001 |
| Urban residents | 16 877 (53.0) | 2015 (50.8) | 143 (52.2) | 100 (44.2) | 0.004 | 15 096 (52.9) | 3463 (54.1) | 231 (48.9) | 340 (47.6) | 0.002 |
| Race | ||||||||||
| Han | 28 741 (90.3) | 3512 (88.6) | 225 (82.1) | 182 (80.5) | <0.001 | 25 282 (88.6) | 5653 (88.3) | 387 (82.0) | 574 (80.3) | <0.001 |
| Tibetan | 678 (2.1) | 132 (3.3) | 21 (7.7) | 11 (4.9) | – | 983 (3.5) | 305 (4.8) | 39 (8.3) | 56 (7.8) | – |
| Uighur | 879 (2.8) | 69 (1.7) | 8 (2.9) | 11 (4.9) | – | 890 (3.1) | 150 (2.3) | 16 (3.4) | 32 (4.5) | – |
| Hui | 594 (1.9) | 200 (5.1) | 17 (6.2) | 14 (6.2) | – | 560 (2.0) | 205 (3.2) | 13 (2.8) | 30 (4.2) | – |
| Zhuang | 924 (2.9) | 51 (1.29) | 3 (1.09) | 8 (3.54) | – | 815 (2.9) | 86 (1.3) | 17 (3.6) | 23 (3.2) | – |
| Income per year, yuan | ||||||||||
| <10 000 | 5726 (18.2) | 867 (22.2) | 56 (20.7) | 74 (33.3) | 0.14 | 6590 (23.4) | 1575 (25.0) | 132 (28.4) | 223 (31.5) | 0.008 |
| 10 000–30000 | 6516 (20.7) | 847 (21.7) | 68 (25.2) | 57 (25.7) | – | 6600 (23.5) | 1539 (24.4) | 104 (22.4) | 184 (26.0) | – |
| >30 000 | 19 210 (61.1) | 2198 (56.2) | 146 (54.1) | 91 (41.0) | – | 14 949 (53.1) | 3185 (50.6) | 229 (49.3) | 301 (42.5) | – |
| Cigarette smoking | ||||||||||
| Never smoked | 15 224 (47.9) | 2298 (58.1) | 164 (59.9) | 114 (50.4) | <0.001 | 27 594 (96.8) | 6212 (97.2) | 456 (96.8) | 686 (96.2) | 0.17 |
| Smoker | 16 585 (52.1) | 1660 (41.9) | 110 (40.1) | 112 (49.6) | – | 922 (3.2) | 176 (2.8) | 15 (3.2) | 27 (3.8) | – |
| Family history of thyroid disease | 1301 (4.1) | 131 (3.3) | 10 (3.7) | 16 (7.2) | 0.011 | 1626 (5.7) | 440 (6.9) | 35 (7.5) | 76 (10.7) | <0.001 |
| Mean body mass index, kg/m2 | 24.5 (0.02) | 24.7 (0.06) | 24.7 (0.22) | 25.3 (0.27) | <0.001 | 23.35 (0.2) | 23.8 (0.05) | 24.2 (0.2) | 24.9 (0.1) | <0.001 |
| Mean UIC, µg/L | 252.1 (4.3) | 321.3 (28.2) | 280.7 (32.1) | 282.4 (27.0) | <0.001 | 244.3 (3.6) | 277.9 (15.5) | 427.6 (133.7) | 221.2 (12.2) | <0.001 |
| Mean TPOAb, IU/mL | 17.19 (0.3) | 41.57 (1.7) | 115.66 (11.7) | 161.01 (14.9) | <0.001 | 28.2 (0.4) | 64.9 (1.7) | 159.0 (9.6) | 202.5 (8.6) | <0.001 |
| Mean TgAb, IU/mL | 30.48 (0.8) | 79.96 (5.3) | 330.58 (54.3) | 407.73 (60.8) | <0.001 | 67.1 (1.4) | 143.4 (5.4) | 381.7 (39.7) | 505.6 (36.0) | <0.001 |
| Median TSH, mIU/L | 2.0 (1.5, 2.7) | 5.2 (4.6, 6.3) | 12.3 (11.0, 16.1) | 10.6 (6.3, 38.5) | <0.001 | 2.2 (1.6, 2.9) | 5.3 (4.7, 6.4) | 12.4 (10.9, 15.4) | 9.8 (5.9, 27.0) | <0.001 |
| Median FT4, pmol/L | 17.0 (15.3, 19.0) | 16.5 (14.9, 18.1) | 14.9 (13.6, 16.4) | 10.8 (8.6, 11.5) | <0.001 | 16.0 (14.6, 17.6) | 15.6 (14.1, 16.9) | 14.0 (12.9, 15.4) | 10.8 (9.2, 11.6) | <0.001 |
| Echogenicity | ||||||||||
| Hypoechogenicity | 381 (1.3) | 130 (3.5) | 22 (8.4) | 28 (12.7) | <0.001 | 732 (2.7) | 418 (6.9) | 57 (12.3) | 141 (20.4) | <0.001 |
| Isoechogenicity | 25 997 (87.8) | 3072 (82.7) | 168 (64.1) | 125 (56.6) | – | 22 800 (85.4) | 4636 (76.7) | 283 (61.3) | 329 (47.5) | – |
| Hyperechogenicity | 1363 (4.6) | 80 (2.2) | 3 (1.1) | 5 (2.3) | – | 712 (2.7) | 61 (1.0) | 6 (1.3) | 9 (1.3) | – |
| Heterogeneous echogenicity | 1872 (6.3) | 433 (11.7) | 69 (26.3) | 63 (28.5) | – | 2457 (9.2) | 929 (15.4) | 116 (25.1) | 213 (30.8) | – |
| Diffuse goitre | 0 (0.0) | 16 (0.4) | 5 (1.8) | 1 (0.4) | <0.001 | 0 (0.0) | 42 (0.7) | 13 (2.8) | 34 (4.8) | <0.001 |
| Nodular goitre | 0 (0.0) | 16 (0.4) | 3 (1.1) | 1 (0.4) | <0.001 | 0 (0.0) | 43 (0.7) | 7 (1.5) | 22 (3.1) | <0.001 |
Data are weighted and expressed as number (%), mean (SE) or median (quartile).
OH, overt hypothyroidism; SCH, subclinical hypothyroidism; TgAb, thyroglobulin antibody; TPOAb, thyroid-peroxidase antibody; UIC, urinary iodine concentration.