Low-density lipoprotein size in primary hypothyroidism. Effects of hormone replacement therapy.

BACKGROUND/AIM: Hypothyroidism is associated with abnormalities in lipid metabolism but its effect on LDL size is not known. This study identified the LDL particle size (pattern 'A' or 'B') in a group of 50 postmenopausal women with primary hypothyroidism before and after 2 months of hormone replacement therapy (HRT) with the aim of establishing whether hypothyroidism is associated with an increased frequency of pattern B LDL compared with healthy controls, and whether euthyroid recovery modified LDL size. METHODS: Lipid parameters (total cholesterol, triglycerides, HDL- and LDL-cholesterol, apoprotein AI and B and lipoprotein(a)) were determined in a blood sample from each patient and control. LDL size was determined by gradient gel electrophoresis. Determinations were done before and after 2 months of HRT (75-150 microg L-tiroxina/daily) in patients and once in controls. RESULTS/CONCLUSIONS: No significant difference emerged in pattern B LDL distribution: 16% in patients and 18% in controls (p = NS). After HRT no statistical variations were observed in LDL size. HRT normalized all other lipid parameters except lipoprotein(a). In conclusion, the increased risk of coronary heart disease assumed to be associated with hypothyroidism is not linked with the presence of pattern B LDL, but rather with concomitant metabolic abnormalities.