Dietary vitamin C intake protects against COPD: the Korea National Health and Nutrition Examination Survey in 2012

Figures & data

Table 1 Demographic characteristics according to the diagnosis of COPD

Variables	Enrolled number	Representing number	Non-COPD	COPD	P-value
Total number	3,283	23,541,704	2,771 (representing 20,082,025)	512 (representing 3,459,679)
Sex					<0.001
Male	1,376	11,252,028	8,604,056 (76.5%)	2,647,971 (23.5%)
Female	1,907	12,289,677	11,477,969 (93.4%)	811,708 (6.6%)
Age (mean ± SD)			54.5±0.4	64.2±0.7	<0.001
Resident district					0.006
Urban	2,556	18,092,613	15,766,726 (87.1%)	2,325,887 (12.9%)
Suburban/rural	727	5,449,091	4,315,299 (79.2%)	1,133,792 (20.8%)
Type of residence					<0.001
General type	1,836	17,367,741	14,484,857 (83.4%)	2,882,884 (16.6%)
Apartment	1,447	6,173,963	5,597,168 (90.7%)	576,795 (9.3%)
Household income					<0.001
Lowest quartile (Q1)	670	4,438,281	3,381,821 (76.2%)	1,056,459 (23.8%)
Low-middle quartile (Q2)	837	6,259,228	5,302,125 (84.7%)	957,103 (15.3%)
High-middle quartile (Q3)	787	5,895,330	5,113,119 (86.7%)	782,211 (13.3%)
Highest quartile (Q4)	949	6,651,449	6,017,045 (90.5%)	634,404 (9.5%)
Educational level					<0.001
Below elementary	1,068	6,840,173	5,289,636 (77.3%)	1,550,537 (22.7%)
Middle school	495	3,255,797	2,688,555 (82.6%)	567,242 (17.4%)
High school	1,008	8,268,662	7,323,906 (88.6%)	944,756 (11.4%)
Above university	707	5,137,213	4,740,069 (92.3%)	397,144 (7.7%)
Marital status					0.261
Married	3,241	23,120,165	19,703,137 (85.2%)	3,417,028 (14.8%)
Unmarried	41	419,691	378,888 (90.3%)	40,803 (9.7%)
Occupation					<0.001
Professional job	344	2,899,674	2,676,419 (92.3%)	223,255 (7.7%)
Office job	169	1,262,324	1,101,149 (87.2%)	161,175 (12.8%)
Service and sales	408	3,387,293	3,184,801 (94.0%)	202,491 (6.0%)
Agriculture and fisheries	339	2,181,427	1,636,043 (75.0%)	545,384 (25.0%)
Technician	303	2,984,528	2,485,055 (83.3%)	499,473 (16.7%)
Laborer	348	2,500,599	2,068,775 (82.7%)	431,824 (17.3%)
Jobless	1,363	8,256,867	6,874,613 (83.3%)	1,382,254 (16.7%)
Smoking history					<0.001
Never smoker	2,012	13,162,867	12,119,987 (92.1%)	1,042,880 (7.9%)
Light smoker	625	5,155,829	4,295,088 (83.3%)	860,741 (16.7%)
Medium smoker	446	3,837,658	2,908,730 (75.8%)	928,928 (24.2%)
Heavy smoker	200	1,385,350	758,220 (54.7%)	627,130 (45.3%)

Abbreviation: SD, standard deviation.

Table 2 Comparison of nutritional status according to the COPD

Nutritional status	Non-COPD (representing number =20,082,025)	COPD (representing number =3,459,679)	P-value
Food intake (g)	1,462.3±23.6	1,320.4±37.9	0.001*
Protein intake (g)	69.4±1.1	67.8±2.4	0.560
Fat intake (g)	36.6±0.9	34.6±2.4	0.407
Carbohydrate intake (g)	322.9±4.2	333.5±7.5	0.180
Calcium intake (mg)	514.0±10.6	492.1±30.2	0.490
Potassium intake (mg)	3,200.0±58.9	2,915.4±85.9	0.005*
Vitamin A intake (μgRE)	1,006.8±65.1	797.3±82.2	0.040*
Carotene intake (μg)	5,392.4±391.3	4,044.9±418.8	0.015*
Retinol intake (μg)	93.4±6.5	63.8±4.9	<0.001*
Vitamin C intake (mg)	122.1±4.0	93.2±3.9	<0.001*

Note:

* P<0.05 between non-COPD and COPD group obtained by independent sample t-test.

Abbreviation: RE, retinol equivalent.

Figure 1 Correlation of the prevalence of COPD with the amount of smoking.

Table 3 Univariate and multivariate analysis for COPD

Variables	Univariate analysis			Multivariate analysis
	OR	95% CI	P-value	OR	95% CI	P-value
Sex			<0.001			<0.001*
Male	Reference			Reference
Female	0.230	0.173–0.306		0.234	0.144–0.378
Age	1.080	1.067–1.094	<0.001	1.089	1.068–1.110	<0.001*
Resident district			0.006			0.601
Urban	Reference			Reference
Suburban/rural	1.781	1.181–2.685		1.137	0.701–1.845
Type of residence			<0.001			0.387
General type	Reference			Reference
Apartment	0.518	0.379–0.707		0.855	0.598–1.222
Household income			<0.001
Lowest quartile (Q1)	Reference			Reference		0.806
Low-middle quartile (Q2)	0.578	0.425–0.785		0.931	0.622–1.392
High-middle quartile (Q3)	0.490	0.335–0.716		1.137	0.709–1.823
Highest quartile (Q4)	0.338	0.225–0.507		1.043	0.633–1.718
Educational level			<0.001			0.354
Below elementary	Reference			Reference
Middle school	0.720	0.524–0.988		0.873	0.550–1.386
High school	0.440	0.308–0.629		0.810	0.512–1.280
Above university	0.286	0.192–0.424		0.601	0.346–1.046
Occupation						0.529
Professional job	Reference		<0.001	Reference
Office job	1.755	0.786–3.918		2.009	0.906–4.455
Service and sales	0.762	0.342–1.697		0.805	0.322–2.012
Agriculture and fisheries	3.996	2.015–7.927		1.153	0.504–2.641
Technician	2.401	1.213–4.785		1.242	0.573–2.694
Laborer	2.502	1.309–4.784		1.230	0.538–2.814
Jobless	2.410	1.365–4.256		1.092	0.534–2.233	0.001*
Smoking history			<0.001
Never smoker	Reference			Reference
Light smoker	2.329	1.641–3.305		1.435	0.925–2.227
Medium smoker	3.711	2.528–5.450		2.192	1.305–3.680
Heavy smoker	9.612	6.368–14.511		2.894	1.641–5.102
Nutrition						0.648
Retinol intake (μg)	0.998	0.996–0.999	0.005	1.000	0.999–1.001	0.001*
Vitamin C intake (mg)	0.996	0.995–0.998	<0.001	0.998	0.996–0.999

Note:

* P<0.05 obtained by multivariate logistic regression analysis.

Abbreviations: OR, odds ratio; CI, confidence interval.

Table 4 Multivariate analysis of COPD according to smoking history and amount of vitamin C intake

Smoking history	Vitamin C intake (mg)	Multivariate analysis
		OR	95% CI	P-value
Never smoker	Lowest quartile (Q1, <48.50)	Reference		0.802
	Low-middle quartile (Q2, 48.50–84.38)	0.906	0.564–1.456
	High-middle quartile (Q3, 84.38–141.63)	0.980	0.559–1.717
	Highest quartile (Q4, >141.63)	0.738	0.377–1.447
Light smoker	Lowest quartile (Q1, <48.50)	Reference		0.011*
	Low-middle quartile (Q2, 48.50–84.38)	1.753	0.707–4.346
	High-middle quartile (Q3, 84.38–141.63)	1.657	0.756–3.630
	Highest quartile (Q4, >141.63)	0.540	0.226–1.290
Medium smoker	Lowest quartile (Q1, <48.50)	Reference		0.786
	Low-middle quartile (Q2, 48.50–84.38)	0.637	0.211–1.921
	High-middle quartile (Q3, 84.38–141.63)	0.612	0.213–1.759
	Highest quartile (Q4, >141.63)	0.655	0.253–1.694
Heavy smoker	Lowest quartile (Q1, <48.50)	Reference		0.019*
	Low-middle quartile (Q2, 48.50–84.38)	0.586	0.138–2.484
	High-middle quartile (Q3, 84.38–141.63)	0.233	0.094–0.576
	Highest quartile (Q4, >141.63)	0.375	0.140–1.004

Note:

* P<0.05 obtained by multivariate logistic regression analysis with adjustment of age and sex.

Abbreviations: OR, odds ratio; CI, confidence interval.