Distribution of potential confounders in cases and controls
| Controls | Cases | Total | |
| Total | 507 (49.3) | 521 (50.7) | 1028 |
| Body mass index | |||
| <20 kg·m−2 | 51 (10.1) | 52 (10.0) | 103 (10.0) |
| 20–25 kg·m−2 | 270 (53.3) | 238 (45.7) | 508 (49.4) |
| 25–30 kg·m−2 | 135 (26.6) | 156 (29.9) | 291 (28.3) |
| ≥30 kg·m−2 | 51 (10.1) | 73 (14.0) | 124 (12.1) |
| Male sex | 239 (47.1) | 206 (39.5) | 445 (43.3) |
| Age yrs | 34.7±7.48 | 32.8±7.37 | 33.7±7.48 |
| Socioeconomic status | |||
| Professional | 242 (47.7) | 186 (35.7) | 428 (41.6) |
| Managerial | 29 (5.7) | 28 (5.4) | 57 (5.5) |
| Skilled | 139 (27.4) | 186 (35.7) | 325 (31.6) |
| Semi-skilled | 29 (5.7) | 29 (5.6) | 58 (5.6) |
| Unskilled | 27 (5.3) | 39 (7.5) | 66 (6.4) |
| Students | 38 (7.5) | 43 (8.3) | 81 (7.9) |
| Smoking | |||
| Never-smoker | 139 (27.4) | 142 (27.3) | 281 (27.3) |
| Exposed to environmental tobacco smoke | 142 (28.0) | 150 (28.8) | 292 (28.4) |
| Ex-smoker | 93 (18.3) | 93 (17.9) | 186 (18.1) |
| Current smoker | 133 (26.2) | 136 (26.1) | 269 (26.2) |
| Supplement use | 106 (20.9) | 123 (23.6) | 229 (22.3) |
Data are presented as n (%) n, or mean±sd.