Fig. 1Serum hemoglobin (Hb) levels according to serum free thyroxine (T4) quartiles in (A) euthyroid men and (B) women. Values are presented as the estimated mean with standard error of the means.
Table 1Baseline Characteristics of Euthyroid Subjects (≥19 Years) Who Underwent Thyroid Function Tests and Serum Hemoglobin Levels Measurements in KNHANES VI (2013 to 2015)
Characteristic |
Total (n = 5,352) |
Men (n = 2,747) |
Women (n = 2,605) |
P value |
Age, yr |
44.0±0.218 |
43.7±0.270 |
44.5±0.295 |
0.024 |
Anemiaa
|
334 (6.1) |
83 (2.8) |
251 (9.9) |
<0.001 |
Serum hemoglobin, g/dL |
14.4±0.023 |
15.4±0.026 |
13.2±0.025 |
<0.001 |
Serum free T4, ng/dL |
1.24±0.003 |
1.28±0.004 |
1.19±0.004 |
<0.001 |
Serum TSH, mIU/L |
2.46±0.019 |
2.36±0.026 |
2.57±0.028 |
<0.001 |
eGFR, mL/min/1.73 m2
|
94.5±0.292 |
94.3±0.354 |
94.7±0.444 |
0.439 |
TPOAb positivitya,b
|
294 (5.2) |
92 (3.3) |
202 (7.3) |
<0.001 |
UIC, μg/L |
280.7 (150.4–650.5) |
272.1 (156.4–609.9) |
273.9 (139.1–635.6) |
0.091 |
Smoking statusb
|
|
|
|
|
Past smoking |
1,030 (19.5) |
883 (31.8) |
147 (5.4) |
<0.001 |
Current smoking |
1,248 (23.6) |
1,080 (39.2) |
168 (5.8) |
|
Comorbidityb
|
469 (8.9) |
290 (10.3) |
179 (7.3) |
<0.001 |
Diabetes |
|
|
|
|
Hypertension |
1,224 (22.9) |
742 (25.6) |
482 (19.7) |
<0.001 |
Chronic kidney disease |
119 (2.4) |
72 (2.6) |
47 (2.2) |
0.356 |
Rheumatoid arthritis |
70 (1.4) |
23 (0.7) |
47 (2.3) |
<0.001 |
Malignancy |
108 (1.9) |
54 (1.6) |
54 (2.1) |
0.297 |
Economic statusb
|
|
|
|
|
Low |
715 (12.8) |
327 (11.0) |
388 (15.0) |
<0.001 |
Middle-low |
1,424 (26.4) |
708 (26.0) |
716 (26.8) |
|
Middle-high |
1,583 (29.9) |
827 (30.6) |
756 (29.1) |
|
High |
1,630 (30.9) |
885 (32.4) |
745 (29.2) |
|
Activity limitationb
|
297 (5.5) |
137 (4.9) |
160 (6.1) |
0.071 |
Table 2Multiple Linear Regression Analysis to Determine Which Covariates Including Serum fT4 Level Are Independently Associated with Serum Hb Level
Independent variable |
Dependent variable: serum Hb |
β |
SE |
P value |
Men |
|
|
|
fT4 |
0.865 |
0.154 |
<0.001 |
Age |
−0.020 |
0.002 |
<0.001 |
eGFR |
−0.005 |
0.002 |
0.005 |
UIC |
<–0.001 |
<0.001 |
0.096 |
TPOAb (>34 IU/mL) |
−0.001 |
0.107 |
0.989 |
Current smoking |
0.201 |
0.044 |
<0.001 |
Comorbidity |
|
|
|
Diabetes |
−0.039 |
0.093 |
0.678 |
Hypertension |
0.135 |
0.065 |
0.038 |
Chronic kidney disease |
−0.478 |
0.202 |
0.019 |
Rheumatoid arthritis |
−0.587 |
0.228 |
0.01 |
Malignancy |
−1.259 |
0.223 |
<0.001 |
Economic status |
0.001 |
0.025 |
0.978 |
Activity limitation |
−0.231 |
0.126 |
0.066 |
Women |
|
|
|
fT4 |
0.842 |
0.184 |
<0.001 |
Age |
0.003 |
0.002 |
0.139 |
eGFR |
−0.005 |
0.002 |
0.004 |
UIC |
<0.001 |
<0.001 |
0.957 |
TPOAb (>34 IU/mL) |
0.154 |
0.101 |
0.128 |
Current smoking |
0.431 |
0.087 |
<0.001 |
Comorbidity |
|
|
|
Diabetes |
0.043 |
0.107 |
0.69 |
Hypertension |
0.203 |
0.067 |
0.003 |
Chronic kidney disease |
−0.406 |
0.259 |
0.118 |
Rheumatoid arthritis |
−0.040 |
0.179 |
0.823 |
Malignancy |
0.002 |
0.192 |
0.999 |
Economic status |
0.001 |
0.028 |
0.961 |
Activity limitation |
0.102 |
0.091 |
0.264 |
Table 3Multiple Logistic Regression Analyses to Determine the ORs of Having Anemia According to Serum fT4 Quartile Categories
fT4 quartiles |
Prevalence, %a
|
Unadjusted Model |
Model 1 |
Model 2 |
OR (95% CI) |
P value |
OR (95% CI) |
P value |
OR (95% CI) |
P value |
Men |
|
|
|
|
|
|
|
Q1 (0.89–1.15) |
5.6 |
6.0 (2.42–14.68) |
<0.001 |
3.9 (1.46–10.24) |
0.007 |
4.4 (1.66–11.73) |
0.003 |
Q2 (1.16–1.26) |
3.2 |
3.3 (1.36–8.16) |
0.009 |
2.7 (1.06–6.92) |
0.038 |
3.0 (1.16–7.62) |
0.024 |
Q3 (1.27–1.38) |
1.7 |
1.8 (0.64–4.97) |
0.274 |
1.5 (0.55–4.34) |
0.417 |
1.7 (0.58–4.73) |
0.344 |
Q4 (1.39–1.76) |
1.0 |
1.0 (reference) |
|
1.0 (reference) |
|
1.0 (reference) |
|
Women |
|
|
|
|
|
|
|
Q1 (0.89–1.08) |
15.4 |
2.4 (1.58–3.70) |
<0.001 |
2.8 (1.78–4.48) |
<0.001 |
2.8 (1.78–4.51) |
<0.001 |
Q2 (1.09–1.18) |
8.7 |
1.3 (0.79–2.04) |
0.326 |
1.3 (0.76–2.11) |
0.367 |
1.3 (0.75–2.10) |
0.389 |
Q3 (1.19–1.28) |
8.7 |
1.3 (0.78–2.04) |
0.351 |
1.2 (0.70–1.95) |
0.543 |
1.2 (0.71–1.96) |
0.512 |
Q4 (1.29–1.76) |
7.0 |
1.0 (reference) |
|
1.0 (reference) |
|
1.0 (reference) |
|
Table 4ORs of Having Anemia According to Serum fT4 Quartile Categories in Younger and Older Participants
fT4 quartiles |
Prevalence, %a
|
ORb (95% CI) |
P value |
Younger (age <50 yr) |
|
|
|
Men (n = 1,658) |
|
|
|
Q1 (0.89–1.18) |
3.2 |
3.3 (1.13–9.75) |
0.029 |
Q2 (1.19–1.30) |
1.6 |
1.0 (reference) |
|
Q3 (1.31–1.41) |
0 |
NA |
<0.001 |
Q4 (1.42–1.76) |
0 |
NA |
<0.001 |
Women (n = 1,619) |
|
|
|
Q1 (0.89–1.09) |
20.3 |
3.2 (1.89–5.49) |
<0.001 |
Q2 (1.10–1.19) |
12.9 |
1.5 (0.83–2.64) |
0.186 |
Q3 (1.20–1.30) |
10.7 |
1.1 (0.61–2.05) |
0.725 |
Q4 (1.31–1.76) |
7.7 |
1.0 (reference) |
|
Older (age ≥50 yr) |
|
|
|
Men (n = 1,089) |
|
|
|
Q1 (0.89–1.10) |
7.5 |
2.0 (0.81–5.19) |
0.131 |
Q2 (1.11–1.20) |
5.9 |
1.8 (0.74–4.42) |
0.198 |
Q3 (1.21–1.31) |
5.6 |
1.4 (0.53–3.71) |
0.503 |
Q4 (1.32–1.76) |
4.1 |
1.0 (reference) |
|
Women (n = 986) |
|
|
|
Q1 (0.89–1.07) |
8.4 |
1.8 (0.74–4.60) |
0.193 |
Q2 (1.08–1.16) |
4.1 |
0.8 (0.29–2.39) |
0.732 |
Q3 (1.17–1.26) |
5.1 |
1.1 (0.37–3.19) |
0.859 |
Q4 (1.27–1.76) |
4.4 |
1.0 (reference) |
|