Clinical and epidemiological studies on thyroid function

The thyroid produces the hormones T4 and T3, regulated by pituitary TSH. In hypothyroidism, too little thyroid hormones are produced. This is associated with cardiovascular disease, partly explained by effects on lipids and blood pressure.

This thesis aims to study effects of thyroid function on cardiovascular risk factors and mortality, and to assess predictors for and optimize treatment of hypothyroidism.

First a study in subjects without thyroid disease is described. Free (F)T4 was related to components of the metabolic syndrome (abdominal obesity, lipids and blood pressure) and to insulin resistance. In this population, the FT4 and FT3 were associated with mortality independent of age and sex.

It is concluded that both thyroid antibodies and TSH are independent predictors for hypothyroidism, even when TSH is normal.

In another study it was found that, also during exercise/stress, no cardiac ischaemia was found in untreated hypothyroid patients. A prospective trial is described 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. The thesis concludes with a general discussion and recommendations for future research.