Table 3.

Multivariate regression models for prediction of log-transformed toenail nicotine levels (ng nicotine/mg toenail) according to different reported smoking variables (n = 2,485)

Model number and tobacco exposureTobacco categorynEstimateSEPR2
Model 1
Smoke exposureNo exposure (reference group)1570.57
SHS exposure among never smokers7680.350.08<0.0001
Current active smoking7712.590.08<0.0001
Model 2
Smoking statusNever smokers (reference group)9880.57
Past smokers7260.070.050.15
Current smokers7712.290.04<0.0001
SHS exposureNo (reference group)315
Yes1,9990.290.06<0.0001
Model 3
No. cigarettes smoked per day0 (reference group)1,7140.59
1-4441.080.14<0.0001
5-141801.800.07<0.0001
15-243062.430.06<0.0001
25-341522.590.08<0.0001
≥35892.800.10<0.0001
Model 4
Frequency of SHS among everyone exposureNo exposure (reference group)3150.61
Occasional1,2270.210.060.002
Frequent7720.460.06<0.0001
No. cigarettes smoked per day0 (reference group)1,714
1-4441.030.14<0.0001
5-141801.760.07<0.0001
15-243062.360.06<0.0001
25-341522.500.08<0.0001
≥35892.700.10<0.0001
Model 5 (among never smokers with SHS frequency data; n = 925)
Frequency of SHS exposureNo exposure (reference group)1570.04
Occasional5380.260.080.001
Frequent2300.580.09<0.0001
Model 6
Composite smoking statusNever smokers (reference group)9880.59
Past smokers7260.070.040.10
Current smokers (1-14 cigarettes per day)2241.690.07<0.0001
Current smokers (15-24 cigarettes per day)3062.460.06<0.0001
Current smokers (25-34 cigarettes per day)1522.620.08<0.0001
Current smokers (≥35 cigarettes per day)892.830.10<0.0001
  • NOTE: Age (y) was significant in all the models. The following were not significant in any model and were excluded from the final models: nail fungus (yes, no), nail polish (yes, no), body mass index (<21, 21-22.9, 23-24.9, 25-28.9, ≥29), physical activity (<1, 1-1.9, 2-3.9, 4-6.9, ≥7 h/wk of moderate to vigorous activity), and alcohol intake (0, 0.1-4.9, 5-14.9, ≥15 g/d).

    There were 169 participants (including 63 never smokers) that did not have information about SHS and were excluded from relevant models.