Clinical and epidemiological studies on thyroid function

The thyroid produces the hormones T4 and T3, regulated by pituitary TSH. In hypothyroidism, too little thyroid hormone is produced. This is associated with cardiovascular disease, partly explained by effects on lipids and blood pressure.Chapter 1 provides an introduction and the aims of the thesis: to study effects of thyroid function on cardiovascular risk factors and mortality, and to assess predictors for and optimize treatment of hypothyroidism.In chapter 2 we describe a study in subjects without thyroid disease: free (F)T4 was related to components of the metabolic syndrome (abdominal obesity, lipids and blood pressure) and to insulin resistance. Chapter 3 shows, in the same normal population, that FT4 and FT3 were associated with mortality, independent of age and sex. In chapter 4 we concluded that both thyroid antibodies and TSH are independent predictors for hypothyroidism, even when TSH is normal.Chapter 5 describes that, also during exercise/stress, no cardiac ischaemia was found in untreated hypothyroid patients. In chapter 6 we describe a prospective trial comparing a full starting T4 dose with a low dose (increased every four weeks) in newly diagnosed cardiac asymptomatic hypothyroidism. Although euthyroidism was reached faster with a full starting dose, symptoms of hypothyroidism and quality of life improved comparably. No cardiac events occurred, so a full starting dose in cardiac asymptomatic patients was safe. Chapter 7 includes an editorial about subclinical thyroid disease and heart failure. Chapter 8 is a general discussion about the topics described in this thesis, with recommendations for future research