Serum lipoprotein and apolipoprotein concentrations and tissue lipoprotein‐lipase activity in overt and subclinical hypothyroidism: the effect of substitution therapy

Abstract

Abstract. Twenty‐one patients with increased, thyroid‐stimulating‐hormone (TSH) concentrations in the serum while fasting were studied before and after substitution with l‐thyroxine. Nine patients had TSH values < 40 mU/1 and an average serum‐thyroxine value of 64 nmol/1. Twelve patients with TSH‐values > 40 mU/1 had an average serum‐thyroxine value of 23 nmol/1. On treatment TSH and thyroxine normalized (reference limits < 8 mU/1 and 65–160 nmol/1 respectively) as did also the response to a load with thyroid‐releasing hormone (TRH). In the group with severe thyroid dysfunction (TSH > 40 mU/1) the lipoprotein‐lipase activities in both adipose and skeletal‐muscle tissue were subnormal before therapy and increased during substitution treatment. This was also reflected in a significant increase of the post‐heparin, lipoprotein‐lipase activity in the plasma and of the fractional removal rate of an i.v. injected fat emulsion. Ten out of twelve patients showed a decrease of the triglyceride concentration in whole serum, which reflected changes of the triglyceride concentrations in low‐density lipoproteins (LDL) and high‐density lipoproteins (HDL) more than changes in very‐low‐density lipoproteins, in which the triglyceride concentration was unchanged during treatment. In LDL, both the cholesterol and triglyceride concentrations were elevated before therapy and decreased by 22% and 32% of the pretreatment values, respectively, during treatment. Furthermore, the serum‐apolipoprotein‐B concentration decreased by 16%. The serum‐apolipoprotein‐A‐I concentration was subnormal before treatment and the lipid composition of the HDL particle was changed towards an enrichment of triglycerides. During treatment, the HDL‐triglyceride concentration decreased, whereas that of HDL cholesterol was unchanged. The fasting serum‐insulin concentration increased significantly during the treatment period. In the group with mild hypothyroidism (TSH < 40 mU/1), there were no significant changes similar to those found in severe hypothyroidism.

Serum Adiponectin Levels and Changes in Glucose Metabolism before and after Treatment for Thyroid Dysfunction

“…In most publications, hypothyroidism has been found to be related to high total cholesterol, LDL cholesterol and triglyceride levels (49,50). The effect of hyperthyroidism on lipid metabolism is opposite to that of hypothyroidism.…”

Association of Diabetes Mellitus and Thyroid Disorders: A Metabolic Prospective

“…ApoB levels are higher in both overt and SCH and have been shown to decrease after L-T4 treatment [93][94]. The lipid abnormalities in overt hypothyroidism are reversible with L-T4 therapy unless the patient has underlying hyperlipidemia [95]. SCH is associated with increased levels of TC and LDL-C [96][97][98][99].…”

The Colorado Thyroid Disease Prevalence Study

“…Suppressed TSH levels have been associated with decreased bone density in some but not all studies 9,10 and with an increased risk of atrial fibrillation 11 and premature atrial beats. 12 It has been known for decades that overt hypothyroidism contributes to ORIGINAL INVESTIGATION elevated serum cholesterol levels, [13][14][15][16][17][18][19][20][21] and recent studies suggest this may also be true with subclinical hypothyroidism. [22][23][24][25][26] However, the impact of various degrees of thyroid dysfunction remains unsettled, perhaps caused in part by differing laboratory definitions and small study populations.…”