It has been reported that euthyroid normolipidemic males and postmenopausal females exhibit significantly higher serum lipoprotein (a) (Lp(a)) levels compared with age- and sex-matched normolipidemic controls. However, it is well known that there is an inverse correlation between Lp(a) concentration and apolipoprotein (a) (apo(a)) isoform size. Thus, it is imperative to exclude differences in apo(a) isoform frequencies between subjects with or without thyroid autoimmunity in order to verify if there is an association between thyroid autoimmunity and increased Lp(a) concentration. To exclude such an effect of different apo(a) isoform frequencies, we determined apo(a) phenotypes in 22 patients (9 males and 13 postmenopausal females) with thyroid autoimmunity and in 64 (29 males and 35 females) age- and sex-matched individuals without thyroid autoimmunity (control group). There were no significant differences in the values of lipid parameters between the two groups, including Lp(a). We did not detect any significant differences in the apo(a) phenotype frequencies between the two groups. Additionally, in neither of the subgroups formed according to the presence of low molecular vs high molecular weight apo(a) isoforms were there any significant differences in median serum Lp(a) levels between patients with and without thyroid autoimmunity. Thus, our results contradict the previously reported association between thyroid autoimmunity and Lp(a) concentrations.
ET Bairaktari, AD Tselepis, HJ Millionis and MS Elisaf
Z Efstathiadou, S Bitsis, HJ Milionis, A Kukuvitis, ET Bairaktari, MS Elisaf and A Tsatsoulis
OBJECTIVE: The significance of dyslipidemia in subclinical hypothyroidism (SH) and the effect of thyroid substitution on lipids remain controversial. The present study aimed to assess the association of SH with lipid abnormalities and to quantify the effect of L-thyroxine therapy on serum lipid profiles. DESIGN: Serum lipid parameters of 66 patients with SH and 75 age- and sex-matched euthyroid controls were evaluated in a cross-sectional study. RESULTS: Patients with SH had higher total cholesterol (TC) (222+/-45 (s.d.) vs 190+/- 32 mg/dl), low-density lipoprotein cholesterol (LDL-C) (139+/-28 vs 118+/-39 mg/dl), apolipoprotein B (149+/-21 vs 139+/-18 mg/dl) and lipoprotein (a) (Lp(a)) (median 12.5 (0.8-101) mg/dl vs 7 (0.8-44) mg/dl) levels compared with euthyroid controls (P<0.05 for all comparisons). In a follow-up study including 37 patients with SH, all measurements were repeated after restoration of a euthyroid state with incremental doses of l-thyroxine. No significant changes in serum lipid profiles were observed except for a decrease in high-density lipoprotein cholesterol (59+/-15 to 55+/-14 mg/dl, P<0.05). However, patients with high pre-treatment TC (> or =240 mg/dl) showed a significant reduction in both TC (278+/-28 vs 257+/-36 mg/dl, P<0.05) and LDL-C (192+/-23 vs 173+/-28 mg/dl, P<0.01) levels. Similar but more pronounced changes were observed in a subgroup of patients with pre-treatment levels of TSH > or =10 microU/ml. Thyroid autoimmunity had no effect on either the baseline or the post-treatment lipid profile. CONCLUSION: Although patients with subclinical hypothyroidism exhibit increased levels of the atherogenic parameters (mainly LDL-C and Lp(a)), thyroid substitution therapy does not seem to significantly improve dyslipidemia in the whole group of patients.