Table 2. Risk of Low Back Pain and Related Low Back Spinal Diseases According to Smoking Status in Men.
| Variable | Nonsmoker group (n = 43,961) | Smoker group (n = 160,105) | p-value |
|---|---|---|---|
| Low back pain (M545) | |||
| Median duration of follow-up (IQR), yr | 5.89 (3.62–8.74) | ||
| No. (%) | 9,654 (21.96) | 35,283 (22.04) | 0.01 |
| Incidence rate per 10,000 person-year (95% CI) | 473.08 (463.64–482.52) | 1729.00 (1710.96–1747.04) | 0.01 |
| Difference per 10,000 person-year (95% CI) | Reference | 1255.92 (1255.76–1256.07) | <0.001 |
| Multivariable-adjusted HR per year (95% CI)* | 1 (Reference) | 1.18 (1.15–1.21) | <0.001 |
| Intervertebral disc disease (M51) | |||
| Median duration of follow-up (IQR), yr | 4.79 (3.14–7.40) | ||
| No. (%) | 4,180 (9.51) | 16,014 (10.00) | <0.001 |
| Incidence rate per 10,000 person-year (95% CI) | 204.84 (198.63–211.05) | 784.75 (772.60–796.90) | <0.001 |
| Difference per 10,000 person-year (95% CI) | Reference | 579.91 (579.81–580.01) | <0.001 |
| Multivariable-adjusted HR per year (95% CI)* | 1 (Reference) | 1.25 (1.21–1.30) | <0.001 |
| Spinal stenosis (M4806, M4807) | |||
| Median duration of follow-up (IQR), yr | 7.64 (5.50–9.73) | ||
| No. (%) | 931 (2.12) | 3,481 (2.17) | 0.004 |
| Incidence rate per 10,000 person-year (95% CI) | 45.62 (42.69–48.55) | 170.58 (164.91–176.25) | 0.004 |
| Difference per 10,000 person-year (95% CI) | Reference | 124.96 (124.91–125.01) | <0.001 |
| Multivariable-adjusted HR per year (95% CI)* | 1 (Reference) | 1.52 (1.41–1.64) | <0.001 |
| Spinal instability (M5326, M5327) | |||
| Median duration of follow-up (IQR), yr | 4.94 (3.26–7.58) | ||
| No. (%) | 915 (2.08) | 3,670 (2.29) | <0.001 |
| Incidence rate per 10,000 person-year (95% CI) | 44.84 (41.93–47.75) | 179.84 (174.02–185.66) | <0.001 |
| Difference per 10,000 person-year (95% CI) | Reference | 135.01 (134.95–135.06) | <0.001 |
| Multivariable-adjusted HR per year (95% CI)* | 1 (Reference) | 1.33 (1.24–1.44) | <0.001 |
| Spondylolisthesis (M4316, M4317) | |||
| Median duration of follow-up (IQR), yr | 6.66 (4.94–8.71) | ||
| No. (%) | 243 (0.55) | 900 (0.56) | 0.023 |
| Incidence rate per 10,000 person-year (95% CI) | 11.91 (10.41–13.41) | 44.10 (41.22–46.98) | 0.023 |
| Difference per 10,000 person-year (95% CI) | Reference | 32.20 (32.17–32.22) | <0.001 |
| Multivariable-adjusted HR per year (95% CI)* | 1 (Reference) | 1.49 (1.23–1.80) | <0.001 |
IQR: interquartile range, CI: confidence interval, HR: hazard ratio.
*HRs were estimated from Cox proportional hazards models adjusted for age, body mass index, total cholesterol, blood sugar, alcohol consumption (five categories based on frequency: never, 2–3 per month, 1–2 per week, 3–4 per week, and everyday), physical activity (five categories based on frequency: never, 1–2 per week, 3–4 per week, 5–6 per week, and everyday), and socioeconomic status (three categories based on income: high, middle, and low).