Table 2 Adjusted odds ratios for sidedness of colorectal cancer (left-sided vs. right-sided) according to smoking history

Cigarette smoking

 Never

30,236/5218

Reference

 < .001

 Ever

9537/1175

1.25 (1.16, 1.34)

Current smoking status

 Non-smokers

30,236/5218

Reference

 < .001

 Ex-smokers

2570/287

0.90 (0.80, 1.02)

 Current smokers

2215/388

1.39 (1.22, 1.58)

 Unknown cessation

4752/500

1.43 (1.29, 1.58)

Number of cigarettes per day

 0

30,236/5218

Reference

.790

  > 0−10

2178/259

1.32 (1.16, 1.52)

 11−20

4382/557

1.19 (1.08, 1.32)

  ≥ 21

1568/181

1.30 (1.11, 1.53)

 Unknown

1409/178

1.24 (1.06, 1.46)

Duration of smoking (years)

 0

30,236/5218

Reference

 < .001

  > 0−15

1025/173

0.98 (0.83, 1.16)

 16−30

4349/551

1.18 (1.07, 1.30)

  > 30

3016/310

1.55 (1.36, 1.76)

 Unknown

1147/141

1.27 (1.06, 1.52)

Smoking index

 0

30,236/5218

Reference

 < .001

  > 0−600

4883/657

1.14 (1.04, 1.25)

  > 600

2777/289

1.46 (1.28, 1.66)

 Unknown

1877/229

1.29 (1.12, 1.49)