A study published recently in PLoS One found no significant association between sustained subclinical thyroid dysfunction and development of carotid plaques in healthy individuals.
The retrospective study aimed to investigate the effect of subclinical hypothyroidism on carotid atherosclerosis, which remains controversial. It enrolled 21,342 subjects with sustained subclinical thyroid dysfunction aged 20 years or older. Thyroid dysfunction was assessed by monitoring serum TSH and FT4 levels and considered sustained if it lasted longer than 6 months. All subjects underwent serum thyroid function tests and carotid artery duplex ultrasonography at Samsung Medical Center in Seoul, Korea, between January 2007 and December 2014.
Cross-sectional evaluation of carotid plaques was performed at baseline for all 21,342 enrolled subjects, of whom 16.3% were women. Thyroid function tests revealed that 20,927 subjects had euthyroidism, 365 had subclinical hypothyroidism, and 50 had subclinical hyperthyroidism. Study participants were followed for 5 years or more, after which the effect of subclinical thyroid dysfunction on baseline, as well as newly developed, carotid plaques was determined.
“Carotid plaques were more common in the subclinical hypothyroidism (55.6%) than the euthyroidism (47.8%) at baseline,” the study investigators wrote in their paper. However, multivariable analysis showed that “thyroid status was not a significant risk for the carotid plaques at baseline.” Rather, in subclinical hypothyroidism, baseline carotid plaques were associated with already recognized cardiovascular risk factors such as age (P <.001), fasting blood glucose (P =.030), systolic blood pressure (P =.023), and creatinine (P =.012).
To confirm the findings obtained in cross-sectional analysis for preexisting carotid plaques, the cumulative incidence of new plaques was calculated in longitudinal analysis of data collected for subjects who were followed for more than 5 years. The analysis revealed no significant differences in the number of new carotid plaques developed over time in subjects with euthyroidism and those with subclinical hypothyroidism (P =.392).
“TSH/FT4 values and sustained subclinical hypothyroidism did not significantly affect the cumulative incidence of new carotid plaques according to follow-up time,” investigators wrote in their paper, noting that “[t]he results remained unchanged in subgroup analysis of severe subclinical hypothyroidism and euthyroidism.” They concluded that “only longer follow-up time was a significant predictor of incident carotid plaques.”
- Selection bias may have affected study results, as study participants were self-selected and came from a health screening center in a tertiary hospital.
- A smaller number of subjects were enrolled in the sustained subclinical hypothyroidism and hyperthyroidism groups compared with the euthyroidism group.
- Drug and disease status were not included in the analysis, although they could have influenced the formation of carotid plaques.
Kim H, Kim TH, Kim HI, et al. Subclinical thyroid dysfunction and risk of carotid atherosclerosis [published online July 27, 2017]. PLoS One. doi: 10.1371/journal.pone.0182090