Association of serum ferritin levels with smoking and lung function in the Korean adult population: analysis of the fourth and fifth Korean National Health and Nutrition Examination Survey

Figures & data

Table 1 Characteristics of study population according to spirometric results

Characteristics	Total	Spirometric results				Obstructive severity
		Normal	Restrictive	Obstructive	P-value	Mild	Moderate	Severe	P-value
Number (%)	15,239	11,477 (75.3)	1,727 (11.3)	2,035 (13.4)		907 (6.0)	1,023 (6.7)	105 (0.7)
Age group (years)
40–49	4,610	4,106 (89.1)	339 (7.4)	165 (3.6)	<0.001	55 (33.3)	108 (65.5)	2 (1.2)	0.323
50–59	4,626	3,736 (80.8)	464 (10.0)	426 (9.2)		175 (41.1)	225 (52.8)	26 (6.1)
60–69	3,728	2,458 (65.9)	540 (14.5)	730 (19.6)		307 (42.1)	390 (53.4)	33 (4.5)
≥70	2,275	1,177 (51.7)	384 (16.9)	714 (31.4)		370 (51.8)	300 (42.0)	44 (6.2)
Sex
Men	6,613	4,325 (65.4)	815 (12.3)	1,473 (22.3)	<0.001	664 (45.1)	728 (49.4)	81 (5.5)	<0.001
Women	8,626	7,152 (82.9)	912 (10.6)	562 (6.5)		243 (43.2)	295 (52.5)	24 (4.3)
Smoking status
Never smoker	9,223	7,569 (82.1)	1,015 (11.0)	639 (6.9)	<0.001	268 (41.9)	347 (54.3)	24 (3.8)	0.029
Exsmoker	3,180	2,026 (63.7)	395 (12.4)	759 (23.9)		358 (47.2)	353 (46.5)	48 (6.3)
Current smoker	2,836	1,882 (66.4)	317 (11.2)	637 (22.5)		281 (44.1)	323 (50.7)	33 (5.2)
Smoking amount (pack-year)
0	9,225	7,571 (82.1)	1,015 (11.0)	639 (6.9)	<0.001	268 (41.9)	347 (54.3)	24 (3.8)	0.002
0–19.9	2,702	1,951 (72.2)	297 (11.0)	454 (16.8)		234 (51.5)	195 (43.0)	25 (5.5)
>20	3,312	1,955 (59.0)	415 (12.5)	942 (28.4)		405 (43.0)	481 (51.1)	56 (5.9)
Anemia
Yes	740	990 (8.6)	175 (10.1)	155 (7.6)	0.023	73 (8.1)	73 (7.1)	9 (8.6)	0.700
No	14,499	10,487 (91.4)	1,552 (89.9)	1,880 (92.4)		834 (92.9)	950 (92.9)	96 (91.4)

Notes: Data are presented as numbers (percentages) for categorical variables. Anemia was defined as <13 g/dL hemoglobin for men and <12 g/dL hemoglobin for women. P-value was calculated using one-way analysis of variance.

Table 2 Serum ferritin levels of study population according to spirometric results by clinical parameters

Characteristics	Spirometric results (n = 15,239)				Obstructive severity (n=2,035)
	Normal	Restrictive	Obstructive	P-value	Mild	Moderate	Severe	P-value
Number (%)	11,477 (75.3)	1,727 (11.3)	2,035 (13.4)		907 (6.0)	1,023 (6.7)	105 (0.7)
Serum ferritin (μg/L)	62.3 (33.9–104.8)	74.6 (42.6–128.3)	83.9 (50.3–138.9)	<0.001	84.4 (50.6–138.9)	83.6 (50.4–139.9)	82.8 (44.5–135.8)	0.901
Age group (years)
40–49	52.8 (21.6–103.3)	64.5 (26.6–138.2)	92.1 (41.2–145.1)	<0.001	89.8 (41.2–154.3)	95.1 (38.1–129.3)	83.1 (63.3–102.9)	0.916
50–59	64.4 (38.2–105.1)	80.3 (48.3–131.4)	83.8 (56.3–139.0)	<0.001	87.4 (59.7–139.0)	81.4 (55.3–146.9)	94.6 (40.1–134.7)	0.718
60–69	67.0 (41.6–106.0)	76.4 (47.3–127.7)	84.2 (49.3–138.5)	<0.001	87.1 (46.2–140.9)	83.7 (51.1–137.9)	75.7 (39.1–114.6)	0.344
≥70	65.8 (39.3–104.3)	77.3 (42.4–117.0)	81.9 (47.4–139.0)	<0.001	80.7 (46.8–135.0)	82.9 (47.8–142.2)	83.1 (48.9–144.6)	0.469
Sex
Men	102.8 (65.8–157.7)	103.9 (66.1–172.9)	98.8 (60.8–157.1)	0.198	97.9 (60.5–156.2)	100.2 (60.9–160.9)	97.4 (53.6–114.9)	0.916
Women	45.3 (24.6–72.9)	54.8 (31.7–89.1)	55.9 (33.6–85.0)	<0.001	56.6 (36.2–89.4)	55.8 (32.6–84.3)	38.3 (30.3–82.4)	0.404
Smoking status
Never smoker	49.5 (26.6–81.1)	59.6 (34.5–99.0)	62.2 (37.5–98.4)	<0.001	62.2 (39.0–99.0)	62.8 (38.0–100.4)	38.7 (25.3–82.4)	0.192
Exsmoker	95.3 (57.9–147.8)	98.1 (62.2–164.6)	94.4 (56.5–155.5)	0.350	92.3 (57.1–154.2)	97.0 (56.3–156.4)	94.9 (51.9–168.6)	0.310
Current smoker	99.1 (60.0–152.0)	106.4 (65.9–180.8)	98.4 (61.1–159.4)	0.029	98.7 (59.2–154.5)	97.6 (63.7–169.0)	122.9 (73.6–138.8)	0.564
Smoking amount (pack-year)
0	49.5 (26.6–81.1)	59.9 (34.5–99.0)	62.2 (37.5–98.4)	<0.001	62.3 (39.0–99.0)	62.8 (38.0–100.4)	38.7 (25.3–82.4)	0.192
0–19.9	90.2 (52.3–140.9)	96.5 (55.0–160.4)	92.3 (51.4–148.6)	0.680	81.4 (49.3–146.5)	99.3 (57.4–153.4)	91.8 (47.7–184.6)	0.838
>20	103.6 (66.1–157.6)	106.4 (68.0–178.7)	97.9 (61.2–162.3)	0.056	99.9 (65.0–159.8)	96.9 (60.1–165.9)	97.0 (59.0–143.7)	0.844

Notes: Data are presented as median and interquartile range. P-value was calculated using one-way analysis of variance.

Table 3 Multivariable linear regression analysis for relationship between serum ferritin levels and FEV₁ and FEV₁/FVC

Variables	FEV1 (%) predicted				FEV1/FVC (%) predicted
	β	SE	P-value	R^2 (adjusted)	β	SE	P-value	R^2 (adjusted)
Serum ferritin (log-transformed)	0.02269	0.00840	0.007	0.6819	0.00294	0.00141	0.037	0.2801
Age (years)	−0.02539	0.00032	<0.001		−0.00289	0.00005	<0.001
Sex (men)	−0.41599	0.01116	<0.001		0.01668	0.00187	<0.001
Smoking amount (pack-year)	−0.00415	0.00023	<0.001		−0.00084	0.00004	<0.001
Height (cm)	0.03225	0.00065	<0.001		−0.00184	0.00011	<0.001
Weight (kg)	0.00130	0.00041	0.001		0.00104	0.00007	<0.001

Note: Serum ferritin level was logarithmically transformed because of the skewed nature of its distribution.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; SE, standard error.