Subclinical hypothyroidism and mortality

Abstract

BACKGROUND: Data regarding the association between subclinical hyperthyroidism and cardiovascular outcomes are conflicting among large prospective cohort studies. Thismight reflect differences inparticipants' age, gender, thyroid-stimulating hormone (TSH) levels or preexisting cardiovascular disease.We aimed to assess the risks of coronary heart disease (CHD) and total mortality associated with subclinical hyperthyroidism. METHODS: We searched MEDLINE and EMBASE without language restrictions, and reference lists of retrieved articles to find prospective cohort studies with baseline thyroid function assessment and follow-up of subsequent total mortality, CHD mortality and CHD events. Individual data on 49,030 participants with 458,686 person-years of follow-up between 1981 and 2007 were supplied from 9 prospective cohorts in the United States, Europe, Australia and Brazil. We examined the risk of CHD events in 22,676 participants from 6 cohorts with available data. Euthyroidism was defined as a TSH 0.45-4.49 mIU/L and subclinical hyperthyroidism as a TSH RESULTS: Among 49,030 adults, 1,300 had subclinical hyperthyroidism (2.7%) and 47,730 had euthyroidism. During follow-up, 7,988 participants died (1,794 of CHD); 3,740 out of 22,676 participants had CHD events. After exclusion of thyroid-altering medication users at baseline (N=239, 0.5% of all participants), age and gender-adjusted risks of total mortality, CHD mortality and CHD events were increased (Table), with limited statistical heterogeneity across studies (I square=0% to 33%). Risks of total and CHD mortality were increased with lower TSH levels (Table), although borderline significant for total mortality (p for trend 0.053 and 0.01, respectively). Risks did not significantly differ by age, gender, race, or preexisting cardiovascular disease. Results were similar after further adjustment for cardiovascular risk factors. CONCLUSION: Subclinical hyperthyroidism is associated with an increased risk of total and CHD mortality. The risks are higher with lower TSH, particularly in those with TSH below 0.10 mIU/L. Future studies should assess which conditions increase the risk of total and cause-specific mortality associated with subclinical hyperthyroidism. (Table Presented).