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

Table 2 Association between 25-hydroxyvitamin D and the FT3/FT4 ratio in multivariable linear models

Exposure	Crude model (model 1), n = 1271		Partially adjusted model (model 2), n = 1271		Fully adjusted model (model 3), n = 577
	β (95%CI)	P value	β (95%CI)	P value	β (95%CI)	P value
25(OH)D	0.045 (0.011-0.079)	0.01043	0.058 (0.022-0.093)	0.00163	0.088 (0.037-0.139)	0.00081
25(OH)D quartile
Q1	Reference		Reference		Reference
Q2	0.894 (0.099-1.690)	0.02776	1.043 (0.253-1.833)	0.00980	0.846 (-0.251 to 1.943)	0.13103
Q3	1.085 (0.290-1.880)	0.00756	1.270 (0.468-2.072)	0.00195	1.517 (0.362-2.671)	0.01029
Q4	0.865 (0.070-1.660)	0.03317	1.129 (0.298-1.959)	0.00785	1.246 (0.074-2.419)	0.03772
P for trend	0.03014		0.00789		0.02381

Outcome: FT3/FT4 × 100 (continuous). Exposure: 25-hydroxyvitamin D [25(OH)D; continuous; β reflects the change in FT3/FT4 × 100 per 1 ng/mL higher 25(OH)D], with additional analyses by quartiles (Q1-Q4; Q1 as reference) and P for trend. Trend tests were obtained by entering the median of each quartile as a continuous term. Model 1: Unadjusted; model 2: Adjusted for age, sex; model 3: Additionally adjusted for body mass index, systolic blood pressure, diastolic blood pressure, glycated hemoglobin (Box-Cox), total cholesterol (Box-Cox), high-density lipoprotein cholesterol (Box-Cox), low-density lipoprotein cholesterol, triglycerides (Box-Cox), estimated glomerular filtration rate (Box-Cox), uric acid (Box-Cox), aspartate aminotransferase (Box-Cox), alanine aminotransferase (Box-Cox), C-reactive protein (Box-Cox), white blood cell count (Box-Cox), visceral fat area (Box-Cox), subcutaneous fat area (Box-Cox), current smoking, and current drinking. Estimates are β (95%CI) with two-sided P values; P < 0.05 was considered statistically significant; bold P values indicate significance. The outcome was modeled as FT3/FT4 × 100 for numerical scaling; inference is unaffected. 25(OH)D: 25-hydroxyvitamin D.