Trends in Prevalence of Thyroid Dysfunction and its Associations With Mortality Among US Participants, 1988-2012

Various dynamic factors could influence the prevalence and distribution of thyroid dysfunction.To provide national estimates and temporal trends in prevalence of thyroid dysfunction over the past 3 decades in US, and determine the impact of thyroid dysfunction on mortality in US adults.A cross-sectional analysis of data from 33,117 participants aged 12 years or older in the NHANES III (1988-1994), 1999-2002, and 2007-2012.The weighted mean age was 41.6 years, and 48.3% were men. In 2007-2012, the prevalence of subclinical and overt hypothyroidism, subclinical and overt hyperthyroidism was 4.3%, 0.33%, 3.2%, and 0.2% respectively. 80% of individuals with thyroid dysfunction were previously undiagnosed. The prevalence of subclinical hypothyroidism and hyperthyroidism was stable, while overt hypothyroidism (0.54% [95% CI 0.35-0.8%] vs. 0.33% [95% CI 0.23-0.48%]) and hyperthyroidism (0.8% [95% CI 0.58-1.1%] vs. 0.2% [95% CI 0.12-0.33%]) were less prevalent in 2007-2012 compared to 1988-1994. Older age, White Americans, obesity, and positivity for TPOAb and TgAb were risk factors for hypothyroidism, while older age, women and Black Americans were risk factors for hyperthyroidism. Over a median follow-up of 17.2 years, no significant association was observed between any type of thyroid dysfunction with the risk of total or cardiovascular mortality. However, among individuals aged 65 years or older, subclinical hypothyroidism was associated with a higher risk of total mortality (HR 1.17, 95% CI 1.00-1.37, P=0.05) and cardiovascular mortality (HR 1.29, 95% CI 1.04-1.62, P=0.02).The prevalence of subclinical thyroid dysfunction remained relatively unchanged, while that of overt thyroid dysfunction decreased. Subclinical hypothyroidism was associated with a higher mortality among individuals aged 65 years or older.