Table 3.

Associations between daily smoking amount, smoking period, pack-years and knee OA* in Korean adults aged 50 years or over in Korean National Health and Nutrition Examination Survey (KNHANES) 2010–2012

		Adjusted for age and sex			Fully adjusted†			Selectively adjusted‡
Factors	n (case)	OR	95% CI	p Value	OR	95% CI	p Value	OR	95% CI	p Value
Daily smoking amount
All
None	1224 (992)	1			1			1
Less than a half-pack (<10 cigarettes)	92 (66)	0.992	0.505 to 1.951	0.9817	1.351	0.603 to 3.029	0.4649	1.122	0.524 to 2.400	0.7675
Less than 1 pack (<20 cigarettes)	111 (72)	0.832	0.440 to 1.576	0.5734	1.140	0.592 to 2.195	0.6954	0.915	0.488 to 1.715	0.7827
1 pack or more	176 (113)	1.257	0.643 to 2.460	0.5034	1.102	0.513 to 2.365	0.8040	1.237	0.603 to 2.537	0.5614
Smoking period
All
None	1224 (992)	1			1			1
<26 years	135 (89)	0.924	0.519 to 1.646	0.7888	0.921	0.509 to 1.668	0.7860	0.943	0.528 to 1.685	0.8436
<40 years	97 (62)	1.083	0.501 to 2.338	0.8394	1.450	0.613 to 3.430	0.3977	1.181	0.536 to 2.605	0.6796
≥40 years	148 (101)	0.947	0.491 to 1.825	0.8698	1.111	0.521 to 2.369	0.7846	0.988	0.484 to 2.019	0.9736
Smoking level§
All
None	1224 (992)	1			1			1
Low smoking level	137 (98)	0.975	0.541 to 1.756	0.933	1.091	0.567 to 2.1	0.794	1.087	0.583 to 2.028	0.7927
Moderate smoking level	114 (70)	0.804	0.394 to 1.642	0.5501	1.186	0.562 to 2.5	0.6545	0.834	0.412 to 1.688	0.613
High smoking level	127 (83)	1.423	0.688 to 2.94	0.3413	1.356	0.602 to 3.053	0.4627	1.421	0.653 to 3.093	0.3764

Multinomial logistic regression analysis.

*Patients who met knee osteoarthritis criteria of current or ex-smokers.

†Adjusted for age, sex, household income, education, occupation, residential area, alcohol drinking, dietary habits, exercise habits, experience of depressive symptoms, body mass index and fasting blood glucose.

‡Backward elimination method was used with significance set at p<0.05.

§Low smoking level (<15 pack-years), moderate smoking level (<32.4 pack-years) and high smoking level (≥32.4 pack-years).