Table 3.

Effect of smoking on menopause among postmenopausal women (KNHANES, 2007–2014)

Variables	Early menopause (< 50 years)		Late menopause (≥50 years)		Logistic regression for early menopause (< 50 years)a			Linear regression for menopausal age (categorical variable)a			Linear regression for menopausal age (continuous variable)a
	n	%	n	%	OR	95% CI		β	SE	p-value	β	SE	p-value
	(mean)	(SD)	(mean)	(SD)
Total	4930	45.9	5767	54.1
Current age, mean (SD)	64.5	0.2	62.8	0.2
Average menopausal age, mean (SD)	45.6	0.1	52.5	0.0
Smoking status
Non-smoker	4447	90.6	5343	93.6	1.00			1.000
Ex-smoker	172	3.7	160	2.9	1.34	1.02	1.77	−0.615	0.365	0.093
Current smoker	236	5.7	175	3.5	1.68	1.30	2.17	−1.137	0.283	<.0001
Total	4855	100.0	5678	100.0
Cigarettes per day
Non-smoker	4447	92.3	5343	95.1	1.00			1.000
< 20 cigarettes	268	6.1	205	3.9	1.61	1.26	2.07	−1.104	0.302	0.000
≥ 20 cigarettes	69	1.5	55	1.0	1.53	1.00	2.33	−0.486	0.444	0.274
Total	4784	100.0	5603	100.0							−0.038	0.019	0.046
Age at smoking initiationb
Non-smoker	3409	89.9	3993	93.1	1.00			1.000
< 20 years	36	1.2	15	0.4	2.93	1.45	5.90	−1.438	0.461	0.002
≥ 20 years	298	8.9	246	6.4	1.43	1.13	1.82	−0.827	0.293	0.005
Total	3743	100.0	4254	100.0							−0.004	0.001	<.0001
Pack-year (total)b
Non-smoker	3409	90.2	3993	93.4	1.00
Below or equal to the median (≤9.8 pack-years)	153	4.9	175	3.4	1.50	1.11	2.01	−0.773	0.342	0.024
Above the median (>9.8 pack-years)	172	4.9	78	3.3	1.57	1.17	2.09	−1.037	0.389	0.008
Total	3734	100.0	4246	100.0							−0.025	0.015	0.103
Pack-year (before menopause)b
Non-smoker	3409	92.0	3993	93.7	1.00			1.000
Below or equal to the median (≤5 pack-years)	133	4.0	107	2.7	1.54	1.11	2.13	−1.076	0.370	0.004
Above the median (>5 pack-years)	123	4.0	131	3.6	1.14	0.83	1.57	0.417	0.340	0.220
Total	3665	100.0	4231	100.0							0.035	0.020	0.077

OR odds ratios, CI confidence interval; ^a Univariate model  ^b Excluded KNHANES 2013-2014 because age at smoking initiation was not surveyed