Associations Between Thyroid and Blood Pressure in Euthyroid Adults: A 9-Year Longitudinal Study

Abstract

Longitudinal studies considering associations between thyroid function in the reference range (RR) with blood pressure (BP) are scarce and contradictory. We aimed to investigate the associations of serum thyrotropin (TSH) and free T4 (FT4) with different components of BP also incident prehyperetension (preHTN) and HTN during a 9-year follow-up. A sum of 2282 euthyroid individuals from an ongoing population-based cohort study were selected. A sex-stratified multivariate generalized estimating equation (GEE) method was employed. Moreover, a multivariate transitional model was used considering preceding BP status as a predictor of dichotomous outcomes of preHTN and HTN. Multivariate-adjusted GEE analysis revealed a decreasing trend for systolic BP (SBP), diastolic BP (DBP), mean arterial pressure (MAP) and pulse pressure (PP) throughout the study period in both men and women, either adjusted for serum TSH or FT4 levels. Serum FT4 within the RR was positively associated with all BP parameters in total population and in men, but serum TSH had a statistically significant mild increasing effect only on SBP, DBP and MAP of men. Multivariate transitional model found no association between serum TSH levels within the reference range (RR) and BP status; regarding serum FT4, a 1 ng/dl higher FT4 was associated with 40% increased risk of preHTN [OR (95% CI), 1.40 (1.02-1.90)], but not with HTN [OR (95% CI), 0.93 (0.80-1.09)]. It is concluded that serum FT4 within the RR is more strongly associated with BP parameters compared to TSH. This association is not consistent between men and women. Moreover, higher FT4 is associated with increased risk of preHTN.

Relationship between thyroid function and elevated blood pressure in euthyroid adults

“…Findings from above studies suggest a U‐shape relationship between THs within the whole range (subclinical and overt hyperthyroidism, euthyroidism, and subclinical and overt hypothyroidism) and BP levels. However, to the best of our knowledge, few studies have analyzed the relationships between THs, TSH levels and elevated BP in euthyroid subjects . In the present study, we found positive linear relationships between FT3, FT4 concentrations within the reference range and elevated BP.…”

“…Few studies have explored the relationships of FT3, FT4, TSH levels with the prevalence ofelevated BP. To the best of our knowledge, only a small‐scale cohort study (n = 2282) investigated whether FT4 and TSH within reference range were risk factors for elevated BP in Tehran population . Their findings indicated that a 1 ng/dL higher FT4 was related to 40% increased risk of elevated BP (OR [95%CI]: 1.40 [1.02‐1.90]), but no significant relationship was observed between TSH and elevated BP.…”

“…The Thr92Ala polymorphism in the type 2 deiodinase, which locally converts the pro‐hormone T4 to the biological active T3, has been linked to BP . However, most of above trial and experiment studies were all focus on subclinical and overt hyperthyroidism, and few studies have aimed to assess the relationships between normal THs, TSH levels and elevated BP in euthyroid subjects . Therefore, further studies are needed to explore the relevant mechanisms under the relationships between normal THs, TSH levels and elevated BP in euthyroid subjects.…”

“…Moreover, several studies have analyzed the relationships between THs, thyroid‐stimulating hormone (TSH), and hypertension in euthyroid adults . However, to the best of our knowledge, only a small‐scale study (n = 2282) assessed the relationships between free thyroxine (FT4), TSH levels and elevated BP in euthyroid subjects . Therefore, it is still unclear how THs are related to elevated BP in euthyroid subjects.…”

Association of thyroid function with white coat hypertension and sustained hypertension

“…In 2018, the meta‐analysis of He et al showed the relationship of TSH with increased clinic systolic and diastolic blood pressures, but it could not explain the high heterogeneity in the results of analysis ( I 2 = 90%) . In addition, many recent clinical studies did not support the results . Moreover, the effect of the two thyroid function indicators free triiodothyronine (FT3) and free thyroxine (FT4), which had a direct action, on the blood pressure was still not known .…”