The Relationship between Thyroid Function and the Risk Factors of Cardiovascular Disease at Female Medical Checkups

Eun Hee Nah; Jeong Gyu Lee

doi:10.3343/kjlm.2009.29.4.286

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Nah and Lee: The Relationship between Thyroid Function and the Risk Factors of Cardiovascular Disease at Female Medical Checkups

Original Article

Korean J Leg Med 2009;29(4):286-292.

Published online: 14 January 2009

DOI: https://doi.org/10.3343/kjlm.2009.29.4.286

The Relationship between Thyroid Function and the Risk Factors of Cardiovascular Disease at Female Medical Checkups

Eun Hee Nah, M.D., Jeong Gyu Lee, M.T.

Korea Association of Health Promotion, Seoul, Korea

Corresponding author: Eun Hee Nah, M.D. Korea Association of Health Promotion, 1097 Hwagok 6-dong, Gangseo-gu, Seoul 157-704, Korea Tel: +82-2-2601-7161, Fax: +82-2-2696-4500 E-mail: cellonah@hanmail.net

Revised 13 February 200919 May 2009 Accepted 26 July 2009

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background:

Thyroid hormones play an important role in regulating lipid and glucose metabolism. Thus this study was conducted to investigate the relationship between the thyroid hormone (FT4) or thyroid stimulating hormone (TSH) and the cardiovascular risk factors and metabolic syndrome in the individuals with subclinical thyroid dysfunction.

Methods:

The female health examinee with normal range of FT4 were classified into three groups according to the level of TSH; euthyroid group (n=4,410), subclinical hypothyroidism group (n=438) and subclinical hyperthyroidism group (n=66). Age, blood pressure, BMI, fasting glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglyceride, lipoprotein(a), and high-sensitivity C-reactive protein (hsCRP) levels of serum specimens were compared among the groups and association of FT4 or TSH with these parameters.

Results:

Fasting glucose was significantly higher in subclinical hyperthyroidism than in euthyroid and subclinical hypothyroidism groups (P=0.031), and total cholesterol was higher in subclinical hypothyroidism than in subclinical hyperthyroidism (P=0.011). But the other factors showed no difference among the groups. The level of TSH increased as triglyceride increased, while FT4 decreased as BMI or triglyceride increased. The FT4 also lowered when fasting glucose was above 126 mg/dL. TSH was not related with the metabolic syndrome, but the possibility of the syndrome was 1.3 times higher in the lowest quartile of the normal range of FT4 than in its highest quartile.

Conclusions:

For the interpretation of FT4, its reference interval needs to be divided into 4 quartiles, which can be used as one of the predicting factors of the metabolic syndrome.

Keywords: Subclinical thyroid dysfunction, FT4, Cardiovascular risk factors, Metabolic syndrome

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Table 1.

Difference of variables among euthyroid and subclinical thyroid dysfunction groups

	Subclinical hyperthyroidism (n=66)	Euthyroid (n=4,410)	Subclinical hypothyroidism (n=438)	P value∗
TSH (μIU/mL)	0.050±0.08	1.978±0.89	5.912±2.32	<0.001
FT4 (ng/dL)	1.406±0.24	1.198±0.15	1.127±0.16	<0.001
Age (yr)	47.1±12.8	43.7±12.9	43.8±13.3	NS
BMI	22.6±3.0	22.7±3.2	22.5±3.2	NS
Systolic BP (mmHg)	119.7±15.8	116.7±16.1	117.6±15.9	NS
Diastolic BP (mmHg)	71.0±9.4	69.2±10.3	70.1±9.9	NS
Fasting glucose (mg/dL)	94.7±20.7^†	90.3±14.0	89.8±15.4	0.031
T. Cholesterol (mg/dL)	170.3±31.7^†	178.7±33.1	181.4±32.9	0.029
LDL-C (mg/dL)	106.3±28.9	113.1±31.9	115.7±31.9	NS
HDL-C (mg/dL)	53.6±10.9	54.4±9.2	54.4±8.8	NS
Triglyceride (mg/dL)	86.0±48.4	91.1±57.9	95.2±52.0	NS
Lp(a) (mg/dL)	13.4±12.6	16.1±18.1	15.9±17.4	NS
hs-CRP (mg/dL)	0.09±0.14	0.15±0.63	0.13±0.26	NS

^∗ P value derived from one-way ANOVA that used to evaluate differences in the 3 groups;

^† P<0.05 from the posthoc comparisons (Dunnett t) of the investigated variables between euthyroid and subclinical hyperthyroidism

Abbreviations: BP, blood pressure; BMI, body mass index; T. cholesterol, total cholesterol; LDL-C, LDL-cholesterol; HDL-C, HDL-cholesterol; Lp(a), lipoprotein(a); hsCRP, high sensitivity C-reactive protein; NS, not significant.

Table 2.

Mean FT4 according to age

Age	N	Mean FT4	P value
20-29	557	1.223±0.165	<0.001
30-39	1,930	1.209±0.155
40-49	750	1.173±0.155
50-59	939	1.175±0.158
60-69	608	1.182±0.162
70-	130	1.171±0.162
Total	4,914	1.194±0.159

Table 3.

TSH levels according to the levels of each cardiovascular risk factor

BMI	TSH (mean±SD)	P value
<23	2.331±1.825	NS
23 to <25	2.479±4.000
25 to <30	2.359±2.880
≥30	3.766±2.086
BP		NS
SBP <130 or DBP <85	2.289±1.528
SBP ≥130 or DBP ≥85	2.354±1.779
Fasting glucose		NS
<100	2.413±3.140
100-125	2.149±1.468
≥126	2.961±7.495
T. Cholesterol		NS
200>	2.379±2.830
200-240	2.497±4.441
>240	2.316±1.479
LDL-C		NS
≤100	2.272±2.332
100 to 130	2.392±2.563
≥130	2.576±4.602
Triglyceride		0.008
<150	2.283±1.586
≥150	2.463±1.586
HDL-C		NS
≥50	2.399±3.428
<50	2.400±2.539

Abbreviations: See Table 1.

Table 4.

FT4 levels according to the levels of each cardiovascular risk factor

BMI	FT4 (mean±SD)	P value
<23	1.217±0.212	<0.001
23 to <25	1.182±0.201
25 to <30	1.187±0.363
≥30	1.151±0.188
BP		NS
SBP <130 or DBP <85	1.197±0.159
SBP ≥130 or DBP ≥85	1.186±0.158
Fasting glucose		<0.001
<100	1.201±0.248
100-125	1.219±0.238
≥126	1.176±0.184
T. Cholesterol		NS
<200	1.209±0.268
200-240	1.179±0.162
>240	1.185±0.171
LDL-C		NS
≤100	1.227±0.328
100 to 130	1.191±0.187
≥130	1.180±0.166
Triglyceride		<0.001
<150	1.199±0.158
≥150	1.156±0.158
HDL-C		NS
≥50	1.201±0.180
<50	1.204 ±0.351

Abbreviations: See Table 1.

Table 5.

Independent associations between FT4 level and metabolic syndrome

FT4 (ng/dL)	People (N)	MS (%)	OR (95% CI) for MS	P value
Q1 (0.800-1.088)	1,185	12.4	1	0.204
Q2 (1.089-1.190)	1,339	10.5	0.927 (0.716-1.200)	0.564
Q3 (1.191-1.300)	1,149	9.2	0.883 (0.668-1.165)	0.378
Q4 (1.301-1.900)	1,138	7.8	0.732 (0.548-0.979)	0.035

Abbreviations: Q, quartile; MS, metabolic syndrome; OR, odds ratio; CI, confidence interval.

Table 6.

Prevalence and odds ratios (95% confidence interval) for each component of metabolic syndrome according to serum FT4 quartiles

Variables		Q1 (lowest)	Q2	Q3	Q4 (highest)
	Prevalence (%)	26.9	22.3	18.8	18.1
Obesity	OR (95% CI)^†	1	0.78 (0.65-0.94)∗	0.63 (0.52-0.77)∗	0.60 (0.49-0.78)∗
	OR (95% CI)^‡	1	0.84 (0.70-1.02)	0.73 (0.59-0.89)∗	0.70 (0.57-0.86)∗
	Prevalence (%)	24.0	22.5	20.5	19.9
Increased	OR (95% CI)^†	1	0.92 (0.76-1.10)	0.81 (0.67-0.99)∗	0.79 (0.65-0.96)∗
BP	OR (95% CI)^†	1	1.07 (0.87-1.31)	1.05 (0.84-1.30)	1.01 (0.81-1.26)
	Prevalence (%)	11.0	11.5	11.2	13.1
Increased	OR (95% CI)^†	1	1.06 (0.83-1.35)	1.02 (0.79-1.32)	1.22 (0.95-1.57)
Fasting glucose	OR (95% CI)^‡	1	1.22 (0.94-1.57)	1.27 (0.97-1.66)	1.56 (1.20-2.03)∗
	Prevalence (%)	15.9	12.5	9.9	8.1
Increased	OR (95% CI)^†	1	0.76 (0.61-0.94)∗	0.59 (0.46-0.75)∗	0.47 (0.36-0.61)∗
Triglyceride	OR (95% CI)^‡	1	0.83 (0.66-1.04)	0.68 (0.53-0.87)∗	0.54 (0.41-0.71)∗
	Prevalence (%)	32.2	32.3	31.2	26.5
Decreased	OR (95% CI)^†	1	1.00 (0.85-1.18)	0.95 (0.80-1.13)	0.76 (0.63-0.90)∗
HDL-C	OR (95% CI)^‡	1	1.01 (0.85-1.19)	0.96 (0.81-1.14)	0.77 (0.64-0.91)∗

^∗ P<0.05 in logistic regression analysis;

^† Non-adjusted;

^‡ Age-adjusted.

Abbreviations: See Table 5.

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