Table 3.
Levels of NK cell activity according to the number of cigarettes smoked and duration of smoking, among current smokers
| Smoking status | NK cell activity (pg/mL) | P-value |
|---|---|---|
| Daily number of cigarettes smoked | ||
| < 10 cigarettes/day (n = 457) | 1,522 (728-2,734) | < 0.001 |
| 10-19 cigarettes/day (n = 874) | 1,468 (629-2,666) | |
| ≥ 20 cigarettes/day (n = 330) | 1,184 (487-2,064) | |
| Duration of cigarette smoking | ||
| < 20 years (n = 685) | 1,514 (686-2,625) | 0.040 |
| ≥ 20 years (n = 976) | 1,334 (567-2,575) | |
| Total number of cigarettes smoked | ||
| < 10 pack-years (n = 738) | 1,537 (706-2,699) | < 0.001 |
| 10-19 pack-years (n = 612) | 1,429 (560-2,664) | |
| ≥ 20 pack-years (n = 311) | 1,175 (534-2,109) | |
| Urinary cotininea | ||
| < 50 ng/mL (n = 190) | 1,906 (857-2,875) | 0.001 |
| ≥ 50 ng/mL (n = 1,148) | 1,423 (629-2,601) | |
| Urinary cotinineb | ||
| < 292 ng/mL (n = 332) | 1,707 (840-2,865) | < 0.001 |
| 292-879 ng/mL (n = 337) | 1,636 (690-2,811) | |
| 880-1,509 ng/mL (n = 334) | 1,348 (590-2,593) | |
| ≥ 1,510 ng/mL (n = 335) | 1,292 (534-2,235) | |
Values are presented as median (interquartile range). The levels of NK cell activity were compared using the non-parametric Mann–Whitney U-test or Kruskal–Wallis test. NK, natural killer. aThere are missing values in 323 individuals. bValues were categorized into four groups by the quartiles of urinary cotinine levels.