Serum 25-hydroxyvitamin D and peripheral thyroid hormone sensitivity in euthyroid type 2 diabetes: Linear estimates and low-range threshold

Table 1 Baseline characteristics across quartiles of the FT3/FT4 ratio

Characteristic	Q1 (n = 331)	Q2 (n = 373)	Q3 (n = 347)	Q4 (n = 357)	P value
Age (years)	55.43 ± 13.13	55.07 ± 13.27	53.21 ± 12.87	51.23 ± 12.39	< 0.001
Sex					< 0.001
Female	143 (43.20)	171 (45.84)	99 (28.53)	110 (30.81)
Male	188 (56.80)	202 (54.16)	248 (71.47)	247 (69.19)
Current drinking					0.005
No	224 (72.0)	245 (71.6)	204 (62.6)	207 (62.3)
Yes	87 (28.0)	97 (28.4)	122 (37.4)	125 (37.7)
Current smoking					0.002
No	230 (74.0)	246 (71.5)	204 (62.6)	211 (63.6)
Yes	81 (26.0)	98 (28.5)	122 (37.4)	121 (36.4)
DBP (mmHg)	74.72 ± 9.31	74.48 ± 9.08	75.80 ± 8.55	76.39 ± 9.11	0.037
SBP (mmHg)	125.68 ± 14.30	127.56 ± 14.43	127.34 ± 13.2	126.71 ± 12.78	0.289
HbA1C	10.47 (8.38-12.28)	9.62 (7.56-11.14)	8.90 (7.34-10.67)	8.32 (7.11-9.80)	< 0.001
TC (mmol/L)	4.49 (3.81-5.47)	4.62 (3.96-5.44)	4.69 (4.04-5.35)	4.67 (3.79-5.51)	0.633
HDL-C (mmol/L)	1.12 (0.93-1.29)	1.10 (0.94-1.33)	1.08 (0.87-1.28)	1.08 (0.93-1.27)	0.245
LDL-C (mmol/L)	2.80 ± 1.05	2.79 ± 1.00	2.81 ± 1.00	2.73 ± 0.99	0.768
TG (mg/dL)	1.61 (1.08-2.66)	1.76 (1.20-2.95)	2.16 (1.38-3.36)	2.05 (1.30-3.60)	< 0.001
eGFR (mL/minute/1.73 m2)	102.12 ± 15.40	102.26 ± 16.26	102.78 ± 14.36	106.89 ± 14.40	< 0.001
UA (μmol/L)	308.60 (253.57-369.17)	305.20 (245.80-371.20)	319.05 (277.42-381.00)	326.60 (274.77-392.47)	0.002
AST(U/L)	17.40 (14.10-24.70)	18.30 (15.22-24.70)	18.70 (15.20-25.42)	21.05 (16.12-29.05)	< 0.001
ALT(U/L)	19.20 (13.30-30.80)	21.70 (15.57-36.60)	23.20 (15.20-37.80)	27.10 (18.25-45.85)	< 0.001
CRP (mg/L)	2.04 (0.99-4.58)	1.56 (0.69-3.70)	1.50 (0.78-3.25)	1.44 (0.71-3.23)	< 0.001
WBC (× 109/L)	6.49 ± 2.14	6.31 ± 1.73	6.44 ± 1.78	6.58 ± 1.91	0.519
WC (cm)	86.60 (81.50-94.00)	89.00 (82.00-95.00)	89.00 (84.00-96.00)	89.10 (84.60-95.50)	< 0.001
VFA (cm2)	86.00 (63.00-110.00)	93.00 (70.00-114.00)	96.00 (72.00-123.00)	99.00 (75.75-122.25)	< 0.001
SFA (cm2)	162.00 (123.00-204.00)	162.50 (126.00-208.25)	168.00 (135.00-220.00)	169.50 (133.75-216.75)	0.038
FT3 (pmol/L)	3.43 ± 0.40	3.84 ± 0.36	4.10 ± 0.38	4.43 ± 0.45	< 0.001
FT4 (pmol/L)	13.83 ± 1.42	12.94 ± 1.18	12.41 ± 1.13	11.65 ± 1.13	< 0.001
TSH (μIU/mL)	1.25 (0.83-1.86)	1.43 (0.99-2.07)	1.41 (1.00-1.99)	1.46 (0.99-2.12)	0.004
BMI (kg/m2)	24.51 ± 3.74	25.12 ± 3.51	25.60 ± 3.58	26.21 ± 4.30	< 0.001
25(OH)D (ng/mL)	22.14 ± 9.73	22.28 ± 7.40	22.68 ± 7.99	23.38 ± 7.70	0.105

Continuous variables are presented as mean ± SD if approximately normal or median (interquartile range) if skewed; categorical variables as n (%). Quartiles (Q1-Q4, from lowest to highest) were defined by the FT3/FT4 ratio. Between-group differences were tested with one-way ANOVA or Kruskal-Wallis tests for continuous variables and χ² tests for categorical variables, as appropriate. Two-sided P < 0.05 was considered statistically significant. All comparisons are descriptive, reflecting distributional differences across quartiles; sample counts may vary by variable due to missing data. No adjustment for multiple comparisons was applied. DBP: Diastolic blood pressure; SBP: Systolic blood pressure; HbA1C: Glycated hemoglobin; TC: Total cholesterol; HDL-C: High-density lipoprotein cholesterol; LDL-C: Low-density lipoprotein cholesterol; TG: Triglycerides; eGFR: Estimated glomerular filtration rate; UA: Uric acid; AST: Aspartate aminotransferase; ALT: Alanine aminotransferase; CRP: C-reactive protein; WBC: White blood cell count; WC: Waist circumference; VFA: Visceral fat area; SFA: Subcutaneous fat area; TSH: Thyroid-stimulating hormone; BMI: Body mass index; 25(OH)D: 25-hydroxyvitamin D.