Subclinical hypothyroidism tied to sustained, masked hypertension, but not WCH

Combining office blood pressure (BP) and ambulatory BP can lead to a more accurate understanding of the characteristics of BP in subclinical hypothyroidism, suggests a study.

“Literature reports show that the incidence of white coat (WCH) and masked hypertension (MHT) is different in different regions and different races, which might explain the controversy over the correlation between office BP and subclinical hypothyroidism,” the researchers said. [Hypertension 2013;62:982-987]

“In addition, putting the research results into clinical practice is the fundamental purpose of clinical research,” they noted.

This observation study enrolled 3,078 adult volunteers between December 2017 and November 2019, of whom 1,431 participants met the eligibility criteria: 104 had subclinical hypothyroidism (S-HYPO group) and 1,327 had euthyroid (euthyroid group). The researchers then measured office BP and monitored 24-h ambulatory BP to analyse the characteristics of BP in subclinical hypothyroidism.

No statistical difference was observed in office systolic (SBP) and diastolic (D)BP between the S-HYPO group and the euthyroid group (p>0.05). On the ambulatory BP level, the daytime SBP, night-time SBP, night-time DBP, 24-h SBP, and 24-h DBP were significantly higher in the S-HYPO group than those in the euthyroid group (p=0.048, p=0.002, p=0.003, p=0.014, p=0.046, respectively), as was the proportion of nondipper BP. [J Hypertens 2021;39:453-460]

In a comprehensive analysis of BP inside and outside the joint clinic, subclinical hypothyroidism was independently associated with sustained hypertension (SHT; p=0.004) and MHT (p=0.002), but not with WCH (p=0.886). These differences persisted after adjusting for age, sex, body mass index, and other confounding factors (p<0.05).

“After dividing hypertension subtypes, such as WCH, MHT, and SHT according to the current European Hypertension Practice Guidelines, multivariate logistic regression analysis revealed that subclinical hypothyroidism was an independent risk factor for MHT and SHT, whereas the proportion of WCH patients in S-HYPO group was lower than that in euthyroid group; however, the observed difference was not statistically significant,” the researchers said.

Of note, subclinical hypothyroidism is driven by increased peripheral vascular resistance and increased cardiac afterload. [Circulation 2017;136:2100-2116]

A previous meta-analysis reported inconsistent results on the relation between subclinical hypothyroidism and hypertension, while earlier research disputes focused on the level of office BP. [Front Endocrinol (Lausanne) 2018;9:454; Clinical Endocrinol 2006;65:486-491]

Furthermore, a study by Polat Canbolat and colleagues found that subclinical hypothyroidism could increase ambulatory BP during the daytime and night-time, extending the association between subclinical hypothyroidism and BP status to the ambulatory BP level outside the clinic. [Acta Cardiol Sin 2017;33:489-494]

Results of the present study could assist clinicians in judging the BP status in subclinical hypothyroidism, according to the researchers. “For example, for patients with subclinical hypothyroidism patients in clinical practice, even if their office BP is normal, the possibility of MHT should be highly suspected.”