Association between serum thyrotropin levels and mortality among euthyroid adults in the United States.

Association between serum thyrotropin levels and mortality among euthyroid adults in the United States.

Thyroid. 2016 Aug 18;

Authors: Inoue K, Tsujimoto T, Saito J, Sugiyama T

Abstract
BACKGROUND: Low thyroid function within the euthyroid range, as well as overt and subclinical hypothyroidism, reportedly increases the risk of cardiovascular disease and mortality. However, the association between low normal thyroid function and mortality remains controversial. This study was performed to elucidate the association between low normal thyroid function and all-cause and/or cause-specific mortalities among US adults.
METHODS: We conducted a prospective cohort study using a nationally representative sample of 12,584 US adults aged ≥ 20 years with TSH levels within the normal range from the National Health and Nutrition Examination Survey (NHANES) III (1988-1994). Associations between TSH tertiles (high, medium, and low normal TSH groups) and mortalities (all-cause, cardiovascular and cancer) were investigated using multivariable Cox models. Stratum-specific analyses were estimated within subgroups defined according to sex (male or female) and baseline age (age < 60 years or age ≥ 60 years). We further conducted the same analysis using continuous NHANES 2001-2002, 2007-2008, and 2009-2010 cohorts which included data of FT4 levels.
RESULTS: Median follow-up period was 19.1 years, with 3,395 all-cause deaths. A significantly higher risk of all-cause mortality (adjusted hazard ratio [HR], 1.27; 95% confidence interval [CI], 1.10-1.47) and cardiovascular (HR, 1.30; 95% CI, 1.02-1.67) and cancer mortality (HR, 1.43; 95% CI, 1.01-2.01) was observed in the high normal TSH group than in the medium normal TSH group. Additionally, the low normal TSH group had an increased risk of all-cause mortality. In stratum-specific analyses, we found a significant association between high normal TSH levels and all-cause mortality among males, females, and participants < 60 years. Continuous NHANES cohorts demonstrated a non-significant increase in the HR for all-cause mortality in the high normal TSH group.
CONCLUSIONS: High normal TSH levels compared with medium normal TSH levels were associated with increased risk of all-cause, cardiovascular, and cancer mortalities over a long-term follow-up period among US adults. This study indicated that the normal range of TSH levels may require reevaluation.

PMID: 27539006 [PubMed - as supplied by publisher]

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