BACKGROUND: Overt hypothyroidism has been associated with arterial hypertension 
and increased arterial stiffness. Results in euthyroid individuals have been 
conflicting. We investigated associations of thyroid function with systolic 
(SAP) and diastolic (DAP) arterial pressure in euthyroid subjects.
METHODS: 311 euthyroid individuals (185 women, mean age 43.9 +/- 9) without a 
history of diabetes attending a preventive medicine program were examined. 
Subjects receiving thyroxine (10.6%) were excluded; 19.3% had hypertension, 43% 
had a family history for hypertension. TSH, fT4, thyroid autoantibodies, 
insulin, glucose were measured. The "fT4.TSH product", which has been suggested 
as a T4 resistance-index, was calculated.
RESULTS: TSH range was 0.1-8, median 1.4 mU/L, fT4 range was 11.5-25.2 pmol/L, 
median 17.4. TSH and the "fT4.TSH product" were positively associated with DAP 
(p < 0.03, for both associations). In the subgroup of individuals with TSH 
levels 0.36-2.5 mU/L, both TSH and the "fT4.TSH product" were positively 
correlated with SAP (r = +0.133 p = 0.044, r = +0.152 p = 0.026) and DAP (r = 
+0.243 p < 0.001, r = +0.252 p < 0.001 respectively); in multivariate analysis 
the "fT4.TSH product" was a significant predictor of DAP independently of 
HOMA-IR and BMI (p < 0.001). Similar associations were found when only the 
non-hypertensive subjects were analysed (p = 0.004). Hypertensive patients had 
higher TSH levels (p = 0.02) and belonged more frequently to the subgroup with 
TSH > 2 mU/L (35.3% vs 21.3%, p = 0.045).
CONCLUSION: In euthyroid individuals the association of thyroid function with 
diastolic arterial pressure remains significant even when a stricter "normal 
range" for TSH levels is considered. The "freeT4.TSH" product appears to be an 
even stronger predictor of DAP, independently of HOMA insulin resistance index 
and obesity.