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Thyroid hormones and mortality risk in euthyroid individuals: the Kangbuk Samsung health study
Yiyi Zhang1, Yoosoo Chang, Seungho Ryu
1Departments of Epidemiology and Medicine (Y.Z., Y.C., S.R., J.C., S.R., E.G.), and Welch Center for Prevention, Epidemiology, and Clinical Research, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205; Department of Occupational Medicine (Y.C., S.R.), Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine. Seoul 110-746, South Korea; Center for Cohort Studies (Y.C., S.R., J.C.), Total Healthcare Center, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul 110-746, South Korea; Department of Health Sciences and Technology (J.C.), Samsung Advanced Institute for Health Sciences and Technology, Sungkyunkwan University, Seoul 135-710, South Korea; Department of Endocrinology and Metabolism (W.-Y.L., E.-J.R.), Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul 110-746, South Korea; Department of Laboratory Medicine (M.J.K.), Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul 110-746, South Korea; National Center for Epidemiology (R.P.-B.), Carlos III Institute of Health and Consortium for Biomedical Research in Epidemiology and Public Health (CIBERESP), 28029 Madrid, Spain; Department of Social and Preventive Medicine (S.R.), Julius Centre University of Malaya, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia; Department of Surgery (W.K.H.), Kangbuk Samsung Hospital and Sungkyunkwan University School of Medicine, Seoul 110-746, South Korea; and Department of Family Medicine (H.S.), Kangbuk Samsung Hospital and Sungkyunkwan University School of Medicine. Seoul 110-746, South Korea.
Context:
Hyperthyroidism and hypothyroidism, both overt and subclinical, are associated with all-cause and cardiovascular mortality. The association between thyroid hormones and mortality in euthyroid individuals, however, is unclear.
Objective:
To examine the prospective association between thyroid hormones levels within normal ranges and mortality endpoints.
Setting And Design:
A prospective cohort study of 212 456 middle-aged South Korean men and women who had normal thyroid hormone levels and no history of thyroid disease at baseline from January 1, 2002 to December 31, 2009. Free T4 (FT4), free T3 (FT3), and TSH levels were measured by RIA. Vital status and cause of death ascertainment were based on linkage to the National Death Index death certificate records.
Results:
After a median follow-up of 4.3 years, 730 participants died (335 deaths from cancer and 112 cardiovascular-related deaths). FT4 was inversely associated with all-cause mortality (HR = 0.77, 95% confidence interval 0.63-0.95, comparing the highest vs lowest quartile of FT4; P for linear trend = .01), and FT3 was inversely associated cancer mortality (HR = 0.62, 95% confidence interval 0.45-0.85; P for linear trend = .001). TSH was not associated with mortality endpoints.
Conclusions:
In a large cohort of euthyroid men and women, FT4 and FT3 levels within the normal range were inversely associated with the risk of all-cause mortality and cancer mortality, particularly liver cancer mortality.
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