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ARIC analysis: Thyroid dysfunction does not increase risk for CVD
Middle-aged adults with varying degrees of hypothyroidism and hyperthyroidism have a cardiovascular risk profile that is similar to those without thyroid dysfunction, according to an analysis of the Atherosclerosis Risk in Communities Study.
“If moderate or severe thyroid dysfunction is usually detected and treated, then there may be little long-term [CV] consequence; however, this requires formal evaluation,” Seth S. Martin, MD, assistant professor of medicine at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, and colleagues wrote. “With respect to mild [thyroid] dysfunction, attempts to clarify the net clinical significance and need for intervention have resulted in long-standing uncertainty and concern for overtreatment. There is a need to better delineate the potential cross-sectional relationships with CVD risk factors as possible intermediaries between thyroid dysfunction and [CV] risk.”
Martin and colleagues analyzed data from 11,359 black and white adults without prior myocardial infarction, stroke or heart failure participating in the Atherosclerosis Risk in Communities (ARIC) study (mean age, 58 years; 58% women; 76% white; 4.8% prescribed thyroid replacement therapy at baseline). Researchers assessed concentrations of thyroid-stimulating hormone, free thyroxine and total triiodothyronine in stored serum samples originally collected from 1990 to 1992. They used multivariable linear regression to assess cross-sectional associations of thyroid function with CV risk factors and Cox regression analysis to assess prospective associations with CV events.
Cross-sectional outcomes were blood pressure, glycemic markers and serum lipids; prospective outcomes were adjudicated fatal and nonfatal MI and stroke. Follow-up occurred through 2014.
Within the cohort, 1,381 (12%) had thyroid dysfunction at baseline, 255 (2.2%) had moderate or severe chemical hypothyroidism, 542 (4.8%) had mild chemical hypothyroidism, 378 (3.3%) had mild chemical hyperthyroidism and 206 (1.8%) had moderate or severe chemical hyperthyroidism.
During a mean 22.5-year follow-up, 1,102 MIs and 838 strokes occurred. Researchers observed a slight increase in MI in participants with a TSH of at least 15 mIU/L, and increased stroke risk in participants with an free T4 level at least 1.2 ng/dL. Overall, there were no significant associations observed between baseline TSH, free T4 or T3 with MI or stroke. Researchers also reported no interaction of thyroid markers with age, sex or race-center with respect to cross-sectional or prospective outcomes; findings persisted in sensitivity analyses excluding participants on thyroid medication at baseline and those on treatments for relevant risk factors.
Researchers found that thyroid function was more strongly associated with blood lipids than BP or glycemic measures. In the setting of a low prevalence of lipid-lowering medication use (5.25), the mean adjusted differences in LDL cholesterol were 15.1 mg/dL (95% CI, 10.5-19.7) and 3.2 mg/dL (95% CI, 0-6.4) in those with moderate or severe and mild chemical hypothyroidism, respectively, when compared with euthyroid adults. Researchers observed an opposite pattern with moderate or severe and mild chemical hyperthyroidism, and similar differences were seen in triglyceride and non-HDL cholesterol measurements, they noted.
“Persons with various degrees of thyroid function, by clinical categories or concentrations of T3, had [CV] outcomes over 2 decades of follow-up that were similar to those with normal thyroid function,” the researchers wrote. “These results support existing guideline recommendations and provide reassurance that clinical management of moderate or severe thyroid disease in the U.S. is effectively mitigating any long-term [CV] consequences.” – by Regina Schaffer
Disclosure: Martin reports being a co-inventor on a pending patent filed by Johns Hopkins University for a novel method of LDL cholesterol estimation. He reports receiving research support from the Aetna Foundation, American Heart Association, Apple, CASCADE FH, Google, and the PJ Schafer Cardiovascular Research Fund, and serving as a consultant for Amgen, Pew Research Center, Quest Diagnostics and Sanofi/Regeneron.