Subclinical hypothyroidism and the metabolic syndrome: A meta-analysis of cross-sectional studies

Table 1 Characteristics of included studies

Studies	Age (yr)	Male (%)	MS criteria	Sample size	Definitionof SCH	Euthyroid			SCH			Inclusion criteria	Exclusion criteria
						No.	MS	mTSH	No.	MS	mTSH
Hergenç et al[5]	51.99	46.70	NCEP /ATPIII	488	TSH > 4.2 μU/mL	465	193	1.12	23	10	7.54	Age > 34 yr	NA
Garduño-Garcia Jde et al[6]	42.3	48.80	NCEP /ATPIII	3033	TSH: 4.5-10 mIU/L	2771	876	NA	262	84	NA	Aged 18-70 yr	Thyroid disease, diabetes, cardiovascular disease, cerebral vascular disease, amputations, pregnancy, corticosteroid use, active liver disease, and renal dysfunction
					FT4: 10-25 pmol/L
Lai et al[7]	NA	NA	NCEP /ATPIII	6254	TSH > 5.0 μU /mL	6123	1871	NA	131	43	8.5	Age > 65 yr	Taking medications for control of glucose, blood pressure, dyslipidemia, and thyroid function
					Normal FT4
Lai et al[8]	45.1	NA	China Diabetes Society	1385	TSH > 4.8 mIU/L	1283	238	NA	102	25	NA	Aged 18-85 yr	History of thyroid disease; Taking medication such as thyroxine/antithyroid drugs, glucocorticoid, antiepileptic and contraceptive drugs; Pregnant/within the first year of postpartum period; Overt hypothyroidism/hyperthyroidism
					Normal FT3/FT4
Liu et al[9]	48.9	38.20	International Diabetes Federation	6339	TSH > 4.5 mIU/L	5801	1236	2	538	138	6.5	Aged 20-88 yr	Pregnant; Severe renal, liver or heart failure, or abdominal ascites; Taking medicines influencing thyroidal function
					Normal FT3/FT4
Waring et al[10]	73.6	47	NCEP /ATPIII	2047	TSH > 0.35 mIU/L	1779	561	NA	268	98	NA	Aged 70-79 yr	Diabetes; Taking medication such as amiodarone, lithium and antithyroid medications

NCEP/ATPIII: National Cholesterol Education Program/Adult Treatment Panel III; TSH: Thyroid-stimulating hormone; MS: Metabolic syndrome; SCH: Subclinical hypothyroidism; FT4: Free thyroxine; FT3: Free triiodothyronine; NA: Not available; mTSH: mean/median thyroid-stimulating hormone level.

Table 2 Components of the metabolic syndrome in each study

Studies	Thyroid function	n	Waist(cm)	BMI(kg/m2)	SBP(mmHg)	DBP(mmHg)	FBG(mmol/L)	TG(mmol/L)	HDL-C(mmol/L)
Hergenç et al[5]	Euthyroid	465	95.4 ± 10.5	29.3 ± 4.5	126.5 ± 20.6	80.9 ± 10.9	5.77 ± 2.30	1.92 ± 1.24	1.14 ± 0.32
	SCH	23	93.0 ± 10.5	29.0 ± 4.2	121.6 ± 23.8	78.8 ± 13.2	5.66 ± 1.51	1.81 ± 1.11	1.16 ± 0.30
Garduño-Garcia Jde et al[6]	Euthyroid	2771	94.21 ± 11.18	28.69 ± 4.5	115 ± 15.12	77.29 ± 10.68	4.90 ± 1.16	2.29 ± 1.73	1.10 ± 0.29
	SCH	262	94.06 ± 11.18	28.98 ± 5.1	118 ± 16.23	78.22 ± 10.87	4.91 ± 0.973	2.59 ± 4.03	1.13 ± 0.29
Lai et al[8]	Euthyroid	1283	80.8 ± 10.3	24.3 ± 3.6	123 ± 18	79 ± 11	5.22 ± 0.03	1.47 ± 0.03	1.33 ± 0.37
	SCH	102	80.7 ± 9.6	24.5 ± 3.3	122 ± 19	77 ± 11	5.12 ± 0.11	1.73 ± 0.12	1.26 ± 0.27
Liu et al[9]	Euthyroid	5801	80.4 ± 11.1	24.4 ± 6.6	126.8 ± 19.2	81.9 ± 11.3	5.2 ± 1.7	1.5 ± 1.6	1.3 ± 0.4
	SCH	538	81.1 ± 12.4	24.8 ± 3.9	130.2 ± 20.8	83.4 ± 12.0	5.3 ± 1.5	1.6 ± 1.7	1.3 ± 0.6

SCH: Subclinical hypothyroidism; BMI: Body mass index; SBP: Systolic blood pressure; DBP: Diastolic blood pressure; FBG: Fasting blood glucose; TG: Triglyceride; HDL-C: High density lipoprotein cholesterol.

Table 3 Sensitivity analysis of the effect of exclusion of individual studies on pooled ORs with 95%CI

Studies excluded	Pooled ORs of remaining studies (95%CI)	P for OR	I2 (%)	χ2	P for χ2
Hergenç et al[5]	1.20 (1.06-1.36)	0.004	0	2.47	0.650
Garduño-Garcia Jde et al[6]	1.25 (1.09-1.44)	0.002	0	0.84	0.934
Lai et al[7]	1.21 (1.06-1.38)	0.005	0	2.34	0.673
Lai et al[8]	1.18 (1.04-1.35)	0.011	0	1.97	0.742
Liu et al[9]	1.15 (0.99-1.35)	0.071	0	1.97	0.742
Waring et al[10]	1.20 (1.03-1.36)	0.018	0	2.40	0.663