Decreased serum TSH levels are not associated with mortality in the adult northeast German population

Abstract

Objective: Results of cohort studies on the association between decreased serum TSH levels and mortality are conflicting. Some studies demonstrated an increased mortality risk in subjects with decreased serum TSH levels, others did not. Even meta-analyses revealed contradictory results. We undertook the present study to investigate the association between decreased serum TSH levels and mortality in the large population-based Study of Health in Pomerania (SHIP). Design and methods: Data from 3651 individuals from SHIP without known thyroid disorders or thyroid treatment were analyzed. Serum TSH, free triiodothyronine, and free thyroxine levels were determined by immunochemiluminescent procedures. Decreased TSH was defined as serum TSH levels below 0.25 mIU/l. Cox regression was used to associate decreased TSH levels with mortality. Results: The median duration of follow-up was 8.5 years (30 126 person years). During follow-up, 299 individuals (6.9%) died corresponding to a death rate of 9.92 deaths per 1000 person years. Survival time was shorter in subjects with decreased serum TSH levels compared to euthyroid individuals. After adjustment for age and sex, however, there was no association between decreased serum TSH levels and all-cause mortality (hazard ratio: 0.95; 95% confidence interval: 0.67; 1.36). Likewise, decreased serum TSH levels were neither associated with cardiovascular nor with cancer mortality. Conclusions: There is no independent association of decreased serum TSH levels with all-cause, cardiovascular, and cancer mortality in the adult northeast German population. Although our study has some strengths, we cannot finally conclude on therapeutical implications in individuals with subclinical thyroid diseases.

Clinical and therapeutic controversies on subclinical hyperthyroidism

“…Unlike the findings of Itterman et al, 43 this study confirms an association between SH and increased general mortality and of cardiovascular origin.…”

“…Ittermann et al 43 analyzed data from 3,651 Germans aged 20-79 years followed for approximately 8.5 years, during which 299 people died. The number of deaths was higher among subjects with TSH levels below the reference values.…”

Higher free thyroxine levels are associated with all-cause mortality in euthyroid older men: the Health In Men Study

“…Several previous reports had not documented an association of subclinical hypothyroidism or higher TSH levels with mortality in men (23,24,25,26,29,30,33). By contrast, in other studies, subclinical hypothyroidism has been reported to be associated with an increased risk of coronary events and mortality (27,28,31).…”

“…Collet et al (3) pooled individual participant data from ten cohorts comprising 52 674 participants for a meta-analysis and found that adults with subclinical hyperthyroidism had an increased risk of all-cause mortality after adjustment for age and sex (HRZ1.29). Individual studies within this meta-analysis have examined middle-aged and older men and women and either measured TSH levels only (23) or measured FT 4 levels selectively in the setting of abnormal TSH levels (24,25) or did not report FT 4 levels as an independent variable in relation to the outcome of mortality (26,27,28,29,30,31). A recent study not included in that meta-analysis did not find associations of subclinical thyroid disease with mortality (32).…”

Impact of Thyroid Dysfunction on Natural Course of Coronary Artery Disease

“…Previously subclinical hypothyroidism was recognized as an independent risk factor for atherosclerosis and myocardial infarction in elderly women (Hak et al, 2000). But results of these studies are sometimes controversial (Biondi, 2010;Cappola et al, 2006;Iervasi et al, 2007;Ittermann et al, 2010) Thyroid hormone excess causes a lot of cardiovascular changes due to both direct and indirect effects on the cardiovascular system (Table 1), and results in neurohormonal activation, including sympathetic nervous system activation. The latter determines increased heart rate and appearance of arrhythmia, especially atrial fibrillation.…”