Abstract
To evaluate incidence of subclinical and overt hyperthyroidism and hypothyroidism. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a prospective cohort study of 15,105 civil servants, examined at baseline and over a 4-year follow-up. This analysis included 9,705 participants with normal thyroid function at baseline, follow-up information about thyroid function and with no report of using drugs that may interfere in the thyroid function. Thyroid function was defined by TSH/FT4 levels or routine use of thyroid hormones/anti-thyroid medications. Annual and cumulative (over 4-year) incidence rates were presented as percentages (95% Confidence Intervals). The incidence of all overt and subclinical thyroid disease was 6.7% (1.73%/year): 0.19% for overt hyperthyroidism (0.048%/year), 0.54% for subclinical hyperthyroidism (0.14%/year), 1.98% for overt hypothyroidism (0.51%/year), and 3.99% for subclinical hypothyroidism (1.03%/year). The incidence of all thyroid diseases was higher in women, when compared to men, with a low women:men ratio (1.36). For Blacks the highest incidence was for overt hyperthyroidism, while for Whites, the highest incidence was for overt hypothyroidism. However, the highest incidence of overt hyperthyroidism was detected in Asian descendants. The presence of antithyroperoxidase antibodies at baseline was associated with higher incidence of overt thyroid diseases. These results showed a high incidence of hypothyroidism, which is compatible with a country with a more-than-adequate iodine intake. The low women:men ratio of the incidence of thyroid dysfunction highlights the importance of the diagnosis of thyroid diseases among men in Brazil.
Highlights
Thyroid dysfunction is a very common disease in the general population worldwide [1,2]
The present study showed, for the first time, a high annual and cumulative incidence of new overt and subclinical hyperthyroidism and hypothyroidism in a large Brazilian cohort after a 4-year follow-up
The results highlighted a higher incidence of hypothyroidism in the country, but a similar incidence of hyperthyroidism compared to other countries worldwide
Summary
Thyroid dysfunction is a very common disease in the general population worldwide [1,2]. There are a considerable number of prevalence studies, data on the incidence of thyroid diseases is still scarce. Few studies have evaluated the incidence of thyroid diseases worldwide, such as subclinical and overt hyperthyroidism and hypothyroidism [3,4]. In Europe, a recent meta-analysis of seven studies reported an incidence of thyroid diseases of 259.12 (254.39-263.9) events per 100,000 per year: 226.2 (222.26-230.17) and 51 (49.23-52.88) events per 100,000 per year for hypothyroidism and hyperthyroidism, respectively [3]. One study from Iran, one of the few low- and middleincome countries with information about incidence of thyroid diseases and known to be iodine-sufficient, reported an incidence of hypothyroidism of 3.3 in women and 2.1 in men per 1,000 persons/year, while the incidence of hyperthyroidism was found to be 3.8 in women and no cases in men per 1,000 persons/year after a 6-year follow-up [4]. The incidence of thyroid disorders is related to the availability of iodine [5,6], selenium and other trace elements [7], chemical contaminants [8], frequency of autoimmune thyroid diseases [9], and genetic risk factors. [10] Incidence varies widely in populations according to the area of residence. [5-7] as recently proposed, subclinical thyroid diseases can be considered a non-classical risk factor for coronary heart disease [11], being associated with all-cause mortality [12-14] and cardiovascular mortality [13,15]
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