Subclinical thyroid dysfunctions are independent risk factors for mortality in a 7.5-year follow-up: The Japanese-Brazilian thyroid study

Division of Endocrinology, Laboratory of Molecular Endocrinology, Department of Medicine, Escola Paulista de Medicina, Federal University of São Paulo, Rua Pedro de Toledo 669, 11o. andar, 04029-032 São Paulo, SP, Brazil.
European Journal of Endocrinology (Impact Factor: 4.07). 12/2009; 162(3):569-77. DOI: 10.1530/EJE-09-0845
Source: PubMed


The currently available data concerning the influence of subclinical thyroid disease (STD) on morbidity and mortality are conflicting. Our objective was to investigate the relationships between STD and cardiometabolic profile and cardiovascular disease at baseline, as well as with all-cause and cardiovascular mortality in a 7.5-year follow-up.
Prospective, observational study.
An overall of 1110 Japanese-Brazilians aged above 30 years, free of thyroid disease, and not taking thyroid medication at baseline were studied. In a cross-sectional analysis, we investigated the prevalence of STD and its relationship with cardiometabolic profile and cardiovascular disease. All-cause and cardiovascular mortality rates were assessed for participants followed for up to 7.5 years. Association between STD and mortality was drawn using multivariate analysis, adjusting for potential confounders.
A total of 913 (82.3%) participants had euthyroidism, 99 (8.7%) had subclinical hypothyroidism, and 69 (6.2%) had subclinical hyperthyroidism. At baseline, no association was found between STD and cardiometabolic profile or cardiovascular disease. Multivariate-adjusted hazard ratios (HRs (95% confidence interval)) for all-cause mortality were significantly higher for individuals with both subclinical hyperthyroidism (HR, 3.0 (1.5-5.9); n=14) and subclinical hypothyroidism (HR, 2.3 (1.2-4.4); n=13) than for euthyroid subjects. Cardiovascular mortality was significantly associated with subclinical hyperthyroidism (HR, 3.3 (1.4-7.5); n=8), but not with subclinical hypothyroidism (HR, 1.6 (0.6-4.2); n=5).
In the Japanese-Brazilian population, subclinical hyperthyroidism is an independent risk factor for all-cause and cardiovascular mortality, while subclinical hypothyroidism is associated with all-cause mortality.

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    • "A similar prevalence was reported in a study from South India [17]. Recently published cross sectional population based studies in adults from China, Mexico, and Brazil reported prevalence of SCH to range from 3.4% to 8.7% [7] [18] [19]. Overt hypothyroidism is associated with increased morbidity and mortality from cardiovascular disease which has been attributed to increased TC and LDL, mainly due to decreased catabolism and turnover [1]. "
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    ABSTRACT: In view of inconsistent reports on the prevalence of dyslipidemia in subclinical hypothyroidism (SCH), we studied lipid abnormalities in Indian subjects with SCH. A cross sectional study of 5343 subjects divided in two groups, Group-1 (age≤18 years) and Group-2 (age>18 years) was undertaken. They were further subdivided on the basis of their thyroid functional status: Normal (Control); SCH with TSH≤10.0mIU/L (SCH-1); and SCH with TSH>10mIU/L (SCH-2). Prevalence of SCH was 14.7%. The only lipid abnormality in children and adolescents was low HDL in subjects with TSH>10mIU/L compared with controls. Serum total cholesterol (TC), and LDL cholesterol (LDL) were significantly higher in adults with TSH>10mIU/L compared to controls. There were no significant changes in lipid parameters in subjects with SCH having TSH≤10.0mIU/L, compared to controls. Serum TSH was positively and FT3 and FT4 were negatively correlated with TC and LDL. Atherogenic lipid abnormalities were observed in adult subjects with SCH-2 (TSH>10.0mIU/L), and not in subjects with SCH-1 who had TSH≤10.0mIU/L in Indian population.
    Clinical biochemistry 07/2011; 44(14-15):1214-7. DOI:10.1016/j.clinbiochem.2011.07.003 · 2.28 Impact Factor
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    ABSTRACT: The association of endogenous subclinical hyperthyroidism (SHyper) with cardiovascular mortality is controversial. This may reflect the different causes of endogenous SHyper in the population studied due to differences in iodine intake, and different selection criteria, e.g. sex, age, and race, the cutoff for serum TSH level, the duration of follow-up, and the presence of co-morbidities. A small sample size of SHyper patients could have caused a low statistical power in some of these studies. In other studies, the results were not adjusted for relevant confounders. Importantly, various meta-analyses have also given conflicting results. This issue of the European Journal of Endocrinology contains two articles that address the association between endogenous SHyper and cardiovascular and total mortality: one study was conducted in a north-eastern German population and the other in a Japanese-Brazilian population. After adjusting for relevant confounders, there was no association between decreased serum TSH levels and all-cause and cardiovascular mortality in the Pomerania study; on the contrary, all-cause mortality and cardiovascular mortality were significantly higher for individuals with SHyper in the Japanese-Brazilian population. Interestingly, both studies had similar characteristics in terms of selection criteria and duration of follow-up. It remains controversial whether or not to treat middle-aged patients with low serum TSH levels. Large prospective randomized controlled double-blind studies of young and middle-aged patients with SHyper and without underlying cardiac disease are required to assess the potential benefits of treating endogenous SHyper in these age groups.
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