Metabolic cardiovascular disease risk factors and their clustering in subclinical hypothyroidism

Summary Objective  A possible association between subclinical hypothyroidism and cardiovascular disease (CVD) has been reported. Monitoring of atomic-bomb survivors for late effects of radiation exposure at the Radiation Effects Research Foundation has provided the opportunity to examine associations between subclinical hypothyroidism and metabolic CVD risk factors. The objective of the study was to evaluate associations between subclinical hypothyroidism and metabolic CVD risk factors, and a cluster of these factors. Design and participants  This was a cross-sectional study of 3549 subjects (mean age 70 years; 1221 men and 2328 women) between 2000 and 2003 comprising 306 subjects with subclinical hypothyroidism and 3243 control euthyroid subjects in Japan. Measurements  We investigated associations between subclinical hypothyroidism and metabolic CVD risk factors such as hypertension, diabetes mellitus, dyslipidaemia and hyperuricaemia, and a cluster of these factors. Results  Subclinical hypothyroidism was not significantly associated with either hypertension, diabetes mellitus or hyperuricaemia defined by taking into account the use of medications in both men and women, but in men it was associated with dyslipidaemia (P = 0·02). We observed a significantly increased odds ratio (OR) for the presence of three or more metabolic CVD risk factors in men with subclinical hypothyroidism after adjusting for age, body mass index (BMI), and smoking status [OR: 1·83, 95% confidence interval (CI): 1·13–2·94, P = 0·01]. The significant associations remained after an additional adjustment for atomic-bomb radiation dose. Conclusions  There appears to be a significant increase in a cluster of metabolic CVD risk factors among people with subclinical hypothyroidism.