Association between Subclinical Hypothyroidism and Incident Hypertension in Women: A Systematic Review and Meta-Analysis

Abstract

Subclinical hypothyroidism (SCH) has been found to be associated with an increased risk of cardiovascular diseases. However, there is no clear consensus on the relationship between SCH and hypertension (HTN). We sought to investigate the association between SCH and incident HTN in women. MEDLINE and EMBASE databases were searched for studies that reported the incidence of HTN in females with SCH versus without SCH. Pooled odds ratio (OR) and 95% confidence interval (CI) of the outcome were obtained using a random-effects model. Studies were also divided into the middle-aged (mean age < 65) and the older (mean age ≥ 65) subgroups, and a subgroup analysis was performed to examine the potential age-effect on the association between SCH and HTN. Nine studies with a total of 21,972 subjects met the inclusion criteria. SCH was found to be positively associated with HTN (OR = 1.32, 95% CI = 1.02-1.71). Such association varied depending on the age of women. In the middle-aged subgroup, SCH was more positively associated with HTN (OR = 1.64, 95% CI = 1.18-2.27), while there was no significant association in the older subgroup (OR = 0.97, 95% CI = 0.80-1.16). Our study showed that the middle-aged females with SCH had an increased risk of HTN, while there was no significant association in the older females with SCH.

Keywords: blood pressure; females; hypertension; meta-analysis; subclinical hypothyroidism; thyroid.

Figure 1

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram for identification, screening, eligibility, and inclusion of studies.

Figure 2

Forest plot of all included studies (n = 9) showing OR for the association between SCH and HTN. OR for each individual study is represented by a solid square (■), while its CI is denoted by a horizontal line. A diamond (◇) denotes the CI for the pooled OR, and the vertical dashed line passes the pooled OR. Abbreviations: OR, odds ratio; CI, confidence interval; SCH, subclinical hypothyroidism; HTN, hypertension.

Figure 3

Publication bias in the whole studies (n = 9). (a) Funnel plot of (ln(OR_i), SE(ln(OR_i))) [denoted by solid circles(●)] for individual studies (i = 1, …, 9). Vertical solid line passes the pooled ln(OR) (=0.277). Left and right dashed lines represents the 95% pseudo confidence limits. (b) Egger’s test for asymmetry of the funnel plot. Solid circles represent (Precision, SND) for individual studies; SND = $\ln \left(\mathrm{OR}\right)/\mathrm{SE}\left(\ln \left(\mathrm{OR}\right)\right)$ and Precision = $1/\mathrm{SE}\left(\ln \left(\mathrm{OR}\right)\right)$. A solid linear regression line is shown, and the vertical line on the SND axis represents the 95% CI for the intercept. Abbreviations: OR, odds ratio; CI, confidence interval; SE, standard error; SND, standard normal deviate.

Figure 4

Sensitivity analysis via exclusion of the study of Harada (2017). Forest plot in a group (n = 8) without the study of Harada (2017). % weights are from the random-effects model in the whole studies (n = 9). OR for each included individual study is denoted by a solid square (■), while its CI is represented by a horizontal line. The centers and the widths of the diamonds (◇) represent the ORs and the CIs for the excluded study of Harada (2017) and the pooled ORs and CIs in the subtotal and the overall cases, respectively.

Figure 5

Subgroup analysis forest plots in the middle-aged (n = 6) and the older (n = 3) subgroups. % weight is from the random-effects model in the whole studies (n = 9). OR for each individual study in each subgroup is denoted by a solid square (■), while its CI is represented by a horizontal line. The centers and the widths of the diamonds (◇) represent the pooled OR and CI in each subtotal case and the overall case, respectively.