Community-based study of the association of subclinical thyroid dysfunction with blood pressure

The relationship between subclinical thyroid dysfunction and blood pressure has been controversial and received unsufficient attention. Thus, we performed a cross-sectional study conducted among 6,992 inhabitants from six districts of Jiangsu Province to investigate the association of subclinical thyroid dysfunction with blood pressure in China. The data from 6,583 subjects (4,115 women and 2,468 men) were included and divided into three groups: euthyroidism (n = 5669, 86.11%), subclinical hyperthyroidism (n = 108, 1.65%), and subclinical hypothyroidism (n = 806, 12.24%). In the groups with subclinical hypothyroidism and hyperthyroidism, systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse pressure were not significantly different from those in the groups with euthyroidism after being adjusted for age, sex, BMI, and smoking status (P > 0.05). More extensively, the SBP and DBP in the group of subclinical hypothyroidism with lower level of TSH (TSH 4.51-10.00 mIU/l, SCH1) were significantly higher than those of participants with euthyroidism (P < 0.05). Multivariable logistic analysis revealed that subclinical hypothyroidism with lower TSH (TSH 4.51-10.00 mIU/l) was an independent risk factor for increased SBP (OR = 1.28, 95% CI 1.03-1.59, P = 0.028). Similar results could not be found between groups of euthyroid and subclinical hypothyroid with higher level of TSH (TSH > 10 mIU/l, SCH2). Further subdivision of the euthyroid group on the basis of a TSH cut-off of 2.5 mIU/l, revealed still no significant difference in blood pressure after adjustment regardless of whether the TSH levels were in the lower reference (TSH 0.40-2.50 mIU/l, n = 4093) or in the upper reference ranges (TSH 2.51-4.50 mIU/l, n = 1576) (P > 0.05). We concluded that subclinical thyroid dysfunction was not associated with blood pressure. Neither subclinical hyperthyroidism nor subclinical hypothyroidism independently predicted increased blood pressure.