No. of studies | No. of subjects | OR (95% CI) | I2 for heterogeneity | p Value for heterogeneity | |
---|---|---|---|---|---|
Smoking measured as | |||||
Primary exposure | 6 | 325 720 | 1.05 (0.83 to 1.32) | 70.2 | <0.001 |
Secondary exposure | 42 | 212 010 | 0.84 (0.77 to 0.92) | 73.2 | 0.002 |
Smoking defined as* | |||||
Ever | 16 | 16 801 | 0.97 (0.85 to 1.11) | 69.7 | <0.001 |
Current | 36 | 525 728 | 0.85 (0.77 to 0.93) | 69.2 | <0.001 |
Past | 12 | 171 365 | 1.02 (0.91 to 1.14) | 34.0 | 0.118 |
Light smoker | 3 | 2003 | 0.58 (0.40 to 0.85) | 0 | 0.382 |
Heavy smoker | 6 | 14 197 | 0.74 (0.61 to 0.89) | 0 | 0.501 |
OA definition† | |||||
Clinical | 3 | 2644 | 1.25 (0.92 to 1.69) | 40.3 | 0.187 |
Radiographic | 23 | 24 873 | 0.79 (0.71 to 0.87) | 61.5 | <0.001 |
Both | 18 | 338 208 | 0.90 (0.75 to 1.08) | 75.4 | <0.001 |
Self-reported | 4 | 172 005 | 1.06 (1.00 to 1.12) | 31.7 | 0.222 |
OA sites | |||||
Knee | 28 | 359 662 | 0.86 (0.77 to 0.96) | 63.2 | <0.001 |
Hip | 13 | 338 053 | 0.90 (0.73 to 1.11) | 54.2 | 0.010 |
Hand | 13 | 16 741 | 0.98 (0.83 to 1.16) | 67.3 | <0.001 |
Spine | 3 | 3179 | 1.10 (0.98 to 1.24) | 52.7 | <0.001 |
Confounding | |||||
Unadjusted | 23 | 38 401 | 0.87 (0.76 to 0.99) | 83.0 | <0.001 |
Adjusted for any‡ | 34 | 525 563 | 0.88 (0.80 to 0.97) | 74.7 | <0.001 |
Adjusted for BMI | 20 | 361 194 | 0.93 (0.82 to 1.06) | 77.7 | <0.001 |
↵* Ever, as defined by the study or where ‘smoker’ was not defined further by the study—current and past smoking not included unless results provided by study; light smoker, ≤10 cigarettes a day; heavy smoker, ≥20 cigarettes a day.
↵† Clinical, clinically defined OA—for example, ACR criteria; radiographic, radiographically defined OA—for example, KL≥2; both, clinically and radiographically defined OA, including knee or hip replacements.
↵‡ Adjusted for age, gender or BMI according to individual papers where results are available.
ACR, American College of Rheumatology; BMI, body mass index; KL, Kellgren–Lawrence; OA, osteoarthritis.