HIGHER FREE THYROXINE LEVELS PREDICT INCREASED ALL-CAUSE MORTALITY IN EUTHYROID OLDER MEN. THE HEALTH IN MEN STUDY

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 437-470-Non-neoplastic Thyroid Disorders
Basic/Clinical
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-447
Bu Beng Yeap*1, Helman Alfonso2, Graeme J Hankey2, Leon Flicker3, Paul E Norman3 and Paul Chubb4
1University of Western Australia, Fremantle, Australia, 2University of Western Australia, 3University of Western Australia, Perth, Australia, 4Fremantle Hospital, Fremantle, Australia
Context

Overt thyroid disease and subclinical thyroid dysfunction have been associated with poorer health outcomes, but the relationship between thyroid hormone levels within the reference range and mortality in older adults remains unclear.

Objective

We examined associations between circulating free thyroxine (FT4) and thyrotrophin (TSH) with all-cause mortality in older men without thyroid disease.

Design

Prospective longitudinal study.

Participants

Community-dwelling men aged 70-89 years resident in Perth, Western Australia, were assessed in 2001-4. Men with thyroid disease or taking thyroid-related medications were excluded from the analysis.

Main outcome measures

Baseline FT4 and TSH levels were assayed (Elecsys 2010 immunoanalyser, Roche Diagnostics Australia, coefficients of variation for FT4 were 4.0% and 5.2% at 14 pmol/L and 37 pmol/L; for TSH 4.5% and 4.2% at 0.4 and 5.0 mIU/L). Incident deaths were ascertained using the Western Australian Data Linkage System. Cox proportional hazards regression was used to examine associations of FT4 and TSH with all-cause mortality. Adjustments were made for age, smoking, body mass index, waist:hip ratio, creatinine, hypertension, diabetes, dyslipidemia and cardiovascular disease.

Results

There were 3,888 men without existing thyroid disease followed for (mean±SD) 6.4±1.5 years, during which time 837 died (21.5%). Men who died had higher baseline FT4 (16.2±2.3 vs 15.8±2.1 pmol/L, p<0.001), but comparable TSH levels (2.4±1.5 vs 2.3±1.5 mIU/L, p=0.335). In the fully-adjusted analysis, higher FT4 predicted all-cause mortality (quartiles Q4 vs Q1-3: FT4 ≥17.32 pmol/L: hazard ratio [HR]=1.21, 95% confidence interval [CI]=1.04-1.42, p=0.015). TSH level did not predict mortality. After excluding men with subclinical hyper- or hypothyroidism there were 3,445 men and 738 died (21.4%). In these euthyroid men, higher FT4 remained independently associated with all-cause mortality (Q4 vs Q1-3: adjusted HR=1.21, 95% CI=1.02-1.42, p=0.026).

Conclusions

In older men not known to have thyroid disease, higher FT4 levels predict all-cause mortality independently of conventional risk factors. After excluding men with subclinical hyper- or hypothyroidism, men with FT4 in the highest quartile experienced higher mortality. Additional research is needed to determine whether this relationship is causal, explore potential underlying mechanisms and clarify the utility of thyroid function testing to stratify mortality risk in ageing men.

Nothing to Disclose: BBY, HA, GJH, LF, PEN, PC

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: BBY is recipient of a Clinical Investigator Award from the Sylvia and Charles Viertel Charitable Foundation, New South Wales, Australia. Hormone assays were funded by research grants from the Fremantle Hospital Medical Research Foundation, Fremantle Hospital, Western Australia, and the Ada Bartholomew Medical Research Trust, University of Western Australia. The Health In Men Study was funded by Project Grants 279408, 379600, 403963, 513823 and 634492 from the National Health and Medical Research Council of Australia. The funding sources had no involvement in the planning, analysis and writing of the manuscript.