Lipids Profile in Subclinical Hypothyroidism
Lipids Profile in Subclinical Hypothyroidism
Overt hypothyroidism is associated with increased risk for cardiovascular disease (CVD) as
 indicated by hypertension, hypercholesterolemia, and increased low-density lipoprotein
 cholesterol (LDL-C) levels. Mild hypothyroidism, also called subclinical hypothyroidism [SH]
 is highly prevalent in elderly subjects, especially in women older than 50 years of age.
 Whether SH is related as a risk for premature CVD is controversial. It was shown that SH is
 associated with elevated lipids levels, particularly LDL-cholesterol. However recent evidence
 suggests that the 'quality' rather than only the 'quantity' of LDL-cholesterol exerts a
 direct influence on the cardiovascular risk. LDL-cholesterol comprises multiple distinct
 subclasses that differ in their atherogenic potential. Thus, the proposed study protocol is
 intended to evaluate the different LDL lipoproteins subclasses in patients with subclinical
 hypothyroidism.
Overt hypothyroidism is associated with increased risk for cardiovascular disease[CVD] as
 indicated by hypertension, hypercholesterolemia, and increased low-density lipoprotein
 cholesterol (LDL-C) levels.However, not all patients have hypertension or abnormal lipid
 profiles, suggesting that other factors may be involved as collagen-induced platelet
 aggregation or relaxation of vascular smooth muscle, elevated plasma homocysteine and C-
 reactive protein [CRP] levels have been reported in overt hypothyroidism and have been
 proposed as an independent risk factor for CVD.

 Subclinical hypothyroidism [SH] is highly prevalent in elderly subjects, especially in women
 older than 50 years of age. Whether SH is related as a risk for premature CVD is
 controversial. Previously, we have demonstrated that SH in middle-aged women is associated
 with hypertension, hypertriglyceridemia, and elevated total cholesterol/HDL- cholesterol
 ratio.SH was associated with elevated plasma total cholesterol and LDL-cholesterol, decreased
 LDL-cholesterol/LDL-triglycerides due to decreased hepatic lipase activity. The influence of
 SH on lipids was directly proportional to the degree of TSH elevation.

 Atherosclerosis is a diffuse disease formerly considered lipid storage disease, actually
 involves an ongoing inflammatory response. Elevated circulating levels of acute phase
 proteins, cytokines, and cell adhesion molecules indicate that inflammatory processes are
 occurring systematically. Metabolic syndrome is a collection of metabolic risk factors,
 probably of more than one cause, that appear to promote the development of atherosclerotic
 CVD. Hypertension, dyslipidemia and hyperglycemia are the most widely recognized
 characteristics of the metabolic syndrome. Individuals with metabolic syndrome manifest a
 prothrombotic state as well as a proinflammatory state. Insulin resistance is recognized as a
 chronic low-level inflammatory state. Insulin action is an important effector mechanism of
 the proinflammatory cytokines in CVD. Insulin resistance was proposed as the common preceding
 factor of hypertension, LDL and HDL-cholesterol, hypertriglyceridemia, abdominal obesity and
 altered glucose metabolism, linking all of these to the development of CVD. Thus,
 inflammation, metabolic syndrome and insulin resistance are strongly associated and play an
 important role in the pathogenesis of atherosclerosis. In a cross-sectional analysis,
 subjects with SH had a significantly higher prevalence of CVD than euthyroid subjects. There
 were more cardiovascular deaths in subjects with SH than in the euthyroid population. These
 data suggest that SH may be an independent risk factor for CVD. It is not clear yet whether
 patients with SH have cardiovascular risk, as do patients with overt hypothyroidism, and
 whether metabolic syndrome and insulin resistance already exist in untreated patients with
 SH.

 This question was recently studied by our group. We evaluated untreated patients with SH. the
 percentage of MS in patients (41.5%) was significantly higher than in controls (12.2%;
 p=0.003]. SH had significantly higher likelihood of cardiovascular risks [odds ratio 6.26,
 95% confidence interval (CI) 1.6 - 4.49, p= 0.008 for MS].

 We conclude that SH is associated with greater probability of MS. Recent evidence suggests
 that the 'quality' rather than only the 'quantity' of LDL exerts a direct influence on the
 cardiovascular risk. LDL comprises multiple distinct subclasses that differ in size, density,
 physicochemical composition, metabolic behaviour and atherogenicity. There are at least four
 major subspecies of LDL (e.g. large LDL-I, medium LDL-II, small LDL-III, very small LDL-IV)
 and the predominance of small dense LDL has been accepted as an emerging cardiovascular risk
 factor.

 Thus, the proposed study protocol is intended to evaluate lipoprotein phenotype and LDL size
 and subclasses in patients with subclinical Hypothyroidism.
Inclusion Criteria:

 -  Subjects with subclinical hypothyroidism

 Exclusion Criteria:

 -  Patients taking L-thyroxin therapy

 -  Patients with known cardiovascular, cerebral or peripheral atherosclerotic disease.