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Background: In this narrative review, we assess published data on subclinical hyperthyroidism (SCHyper) and its association with cardiovascular disease (CVD) in the general population. Summary: We present data on the risk of SCHyper in relation to CVD outcomes, including atrial fibrillation (AF), heart failure, stroke, coronary heart disease (CHD), major adverse cardiac events (MACE), CVD mortality, and all-cause mortality. Evidence indicates that SCHyper is associated with an elevated risk of AF, heart failure, MACE, CVD mortality, and all-cause mortality. SCHyper appears to have little association with stroke risk and has shown conflicting results regarding CHD risk. Regarding the degree of serum TSH suppression, evidence shows a higher risk of CVD in SCHyper individuals with suppressed TSH (<0.1 mIU/L) compared with those with low TSH (0.1–0.4 mIU/L). Despite evidence that older individuals are inherently at a higher risk for CVD, no studies have yet demonstrated an age-related increase in the relative risk of CVD in SCHyper. Conclusion: The studies indicate that SCHyper is associated with an increased risk of AF, heart failure, MACE, CVD mortality, and all-cause mortality. Considering the importance of the degree of serum TSH suppression and age as risk factors for CVD, treatment decisions should be individualized based on their specific risk factors. [ABSTRACT FROM AUTHOR]

Background: Hypothyroidism is common, and in iodine-sufficient areas, it is primarily caused by autoimmune destruction of the thyroid gland. Observational studies have consistently shown an inverse association between serum 25-hydroxyvitamin D concentration and autoimmune diseases; however, there is a lack of evidence from randomized controlled trials to support a benefit of vitamin D supplementation, particularly for autoimmune thyroid diseases. We, therefore, aimed to assess the effect of vitamin D supplementation on the incidence of hypothyroidism. Methods: We analyzed data from the D-Health Trial (n = 21,315), a randomized double-blind placebo-controlled trial of 60,000 international units per month of supplemental vitamin D3 among Australians aged 60 years and over. Hypothyroidism, a tertiary outcome of the D-Health Trial, was defined by treatment with levothyroxine, ascertained through linkage with the Australian Pharmaceutical Benefits Scheme. The outcome was time to first prescription of levothyroxine. We began follow-up at 12 months after randomization; people who had died or who had been dispensed levothyroxine during the first year were excluded. Flexible parametric survival models were used to assess the effect of vitamin D supplementation on hypothyroidism, overall and within strata defined by age, sex, body mass index, and predicted baseline vitamin D status. Results: We included 17,851 participants in the main analysis (vitamin D = 8939; placebo = 8912). During a median follow-up of 4.1 years (interquartile range 4.1–4.1), 293 participants developed hypothyroidism (vitamin D = 138 [1.5%]; placebo = 155 [1.7%]). Vitamin D supplementation did not significantly reduce the incidence of hypothyroidism (overall hazard ratio [HR] 0.89; 95% confidence interval [CI] 0.71–1.12). There was some suggestion of an effect in females (overall HR 0.78; CI 0.58–1.06) but not in males (overall HR 1.06; CI 0.74–1.50; p interaction 0.20). Conclusions: Vitamin D supplementation did not reduce the incidence of hypothyroidism overall; however, the possible beneficial effect observed in females warrants further investigation. Clinical Trial Registration: Australian New Zealand Clinical Trials Registry: ACTRN12613000743763. [ABSTRACT FROM AUTHOR]

Background: Thyroid cancer incidence has increased in many parts of the world since the 1980s, as has the prevalence of obesity. Evidence suggests that people with greater body size have higher thyroid cancer risk. However, it is unclear whether this association is causal or is driven by over-diagnosis of indolent cancers, because overweight/obese people use health services more frequently than those of normal weight, thus conferring greater opportunity for incidental diagnosis. Assessing whether obesity is associated with higher-risk thyroid cancers might help clarify this issue. Methods: We recruited 1013 people diagnosed with thyroid cancer between 2013 and 2016 and 1057 population controls, frequency matched by sex and age group. We used logistic regression to assess the association between body mass index (BMI) and overall thyroid cancer risk as well as by tumor BRAF mutational status as a marker of potentially higher-risk cancer. Results: Overall, obesity was associated with greater risk of thyroid cancer (odds ratio [OR] = 1.72; 95% confidence interval [CI 1.37–2.16] for obese vs. normal BMI). The association with obesity was significantly stronger for BRAF-mutation positive than BRAF-negative papillary thyroid cancers (PTCs; OR = 1.71 [CI 1.17–2.50] for BRAF-positive vs. BRAF-negative cancers). The increased risks associated with overweight/obesity did not vary by histological subtypes or presence/absence of adverse tumor histologic features. Conclusions: Greater risk of BRAF-mutated PTCs among those with high BMI suggests that the association may not merely reflect greater health care service use and indicates an independent relationship between obesity and clinically important thyroid cancer. [ABSTRACT FROM AUTHOR]