The relationship between serum cholesterol and serum thyroid hormones in male patients with suspected hypothyroidism

Prevalence of thyroid dysfunction among greek type 2 diabetic patients attending an outpatient clinic

Background

The aim of the present study was to determine the prevalence of thyroid dysfunction in patients with type 2 diabetes (T2D) attending an outpatient clinic.

Methods

We examined thyroid dysfunction in a total of 1,092 patients with T2D.

Results

Prevalence rate of thyroid dysfunction was 12.3%. In the group with thyroid dysfunction there was an excess of females in comparison with the group without thyroid dysfunction (P < 0.001). In addition, patients with thyroid dysfunction had higher values of body mass index (P = 0.03) and HDL-cholesterol levels (P = 0.01), and lower values of LDL-cholesterol levels (P = 0.001) in comparison with patients without thyroid dysfunction. Multivariate analysis demonstrated that presence of thyroid dysfunction was related with gender (OR: 0.220, 95% CI: 0.141 - 0.352) and LDL-cholesterol levels (OR: 0.990, 95% CI: 0.985 - 0.995).

Conclusions

The prevalence of thyroid dysfunction among Greek diabetic patients is 12.3%. Diabetic women were more frequently affected than men. Presence of thyroid dysfunction was associated with lower levels of LDL-cholesterol concentrations.

Keywords

Type 2 diabetes mellitus; Thyroid dysfunction; Hypothyroidism; Gender; LDL-cholesterol; Greece

Prevalence and progression of subclinical hypothyroidism in women with type 2 diabetes: the Fremantle Diabetes Study

OBJECTIVE

To assess the prevalence and progression of subclinical hypothyroidism in women with type 2 diabetes.

DESIGN AND PATIENTS

Cross-sectional and longitudinal observational assessment of thyroid function in 420 adult females with type 2 diabetes randomly selected from participants in the community-based Fremantle Diabetes Study. Measurements Serum TSH, antibodies to thyroperoxidase (anti-TPO) and serum free T4 were measured at baseline and after 5 years. Baseline glycated haemoglobin (HbA(1c)), serum glucose, serum total and high density lipoprotein (HDL) cholesterol, serum triglycerides and antibodies to glutamic acid decarboxylase (anti-GAD) were also used in analyses.

RESULTS

After exclusion of patients with known thyroid disease or taking amiodarone or lithium at baseline, the prevalence of subclinical hypothyroidism (a raised serum TSH and normal serum free T4) was 8.6%. Subclinical hypothyroidism was associated with anti-TPO status and age, but there were no independent associations with serum cholesterol, history of coronary heart disease, HbA(1c) or hypoglycaemic therapy. In the subgroup of patients restudied after 5 years, none of those who had subclinical hypothyroidism at baseline had overt hypothyroidism regardless of anti-TPO status.

CONCLUSIONS

In women with type 2 diabetes without known thyroid disease, subclinical hypothyroidism is a common but incidental finding. The routine screening of thyroid function in type 2 diabetes is questionable.

The secondary dyslipidemia and deranged serum phosphate concentration in thyroid disorders

Hyperlipidemia is a secondary disorder associated with many metabolic disorders including hypothyroidism. The occurrence of dyslipidemia in subclinical hypothyroidism is controversial. Hyperphosphatemia may accompany the dyslipidemia in some metabolic disorders. Both hyperlipidemia and hyperphosphatemia are considered to be risk factors for the coronary heart diseases. In the present study, we investigated the occurrence of dyslipidemia and altered serum phosphate concentrations in patients with thyroid disorders. The results indicated a significantly elevated serum cholesterol and triglyceride concentrations in the hypothyroid patients. The dyslipidemia was accompanied with significantly elevated serum phosphate level. On the other hand, no significant difference was evident in the serum lipid or phosphate concentrations of subclinical hypothyroid patients compared to euthyroid subjects. A significantly reduced serum phosphate level was shown in hyperthyroid patients with unaltered serum lipid levels. Significant correlations were evident between TSH and T(4) levels as independent parameters and the serum concentrations of triglyceride, cholesterol and phosphate. The results indicate in hypothyroidism that a secondary hyperphosphatemia may aggravate myocardial and arterial abnormalities induced by the secondary hyperlipidemia, which may need correction.

Subclinical Hypothyroidism and Cardiovascular Risk

Subclinical hypothyroidism (SH), defined by elevated serum levels of thyroid stimulating hormone (TSH) with normal levels of free thyroid hormones, is common in adults, especially in women over 60 years of age. Among individuals with this condition, up to two-thirds have serum TSH levels between 5-10 mU/L and thyroid autoantibodies; almost half of them may progress to overt thyroid failure, the annual percent risk increasing with serum TSH level. There is evidence that elevated TSH levels in patients with SH do not reflect pituitary compensation to maintain euthyroidism, but a mild tissue hypothyroidism sensu strictu. When lasting more than 6-12 months, SH may be associated with an atherogenic lipid profile, a hypercoagulable state, a subtle cardiac defect with mainly diastolic dysfunction, impaired vascular function, and reduced submaximal exercise capacity. The deviation from normality usually increases with serum TSH level ('dosage effect' phenomenon). Restoration of euthyroidism by levothyroxine (LT4) treatment may correct the lipid profile and cardiac abnormalities, especially in patients with an initially higher deviation from normality and higher serum TSH levels. Importantly, a strong association between SH and atherosclerotic cardiovascular disease, independent of the traditional risk factors, has been recently reported in a large cross-sectional survey (the Rotterdam Study). However, whether SH confers a high risk for cardiovascular disease, and whether LT4 therapy has a long-term benefit that clearly outweighs the risks of overzealous treatment in these individuals, remain topics of controversy. Therefore, until randomized, controlled, prospective, and adequately powered trials provide unequivocal answers to these critical questions, it is advisable to prescribe LT4 therapy on a case-by-case basis, taking into account the risk of progressive thyroid failure and the risk of cardiovascular events.

Clinical review 115: effect of thyroxine therapy on serum lipoproteins in patients with mild thyroid failure: a quantitative review of the literature

The objective of our study was to estimate the expected change in serum lipoprotein concentrations after treatment with T4 in patients with mild thyroid failure (i.e. subclinical hypothyroidism). Our data sources included MEDLINE, between January 1966 and May 1999, and review of references from relevant articles. There were 1,786 published studies identified, 461 abstracts reviewed, 74 articles retrieved, 24 articles evaluated against predetermined entry criteria, and 13 studies systematically reviewed and abstracted. All studies reported serum total cholesterol concentration changes during T4 treatment, 12 reported triglyceride changes, 10 reported high-density lipoprotein (HDL) cholesterol changes, and 9 reported low-density lipoprotein (LDL) cholesterol changes. There were 247 patients in 13 studies. The mean decrease in the serum total cholesterol concentration was -0.20 mmol/L (-7.9 mg/ dL), with a 95% confidence interval of -0.09 to -0.34. The decline in serum total cholesterol was directly proportional to its baseline concentration. Studies enrolling hypothyroid participants receiving suboptimal T4 doses reported significantly larger decreases in serum total cholesterol after thyroid-stimulating hormone normalization than studies enrolling previously untreated individuals with mild thyroid failure [-0.44 mmol/L (-17 mg/dL) vs. -0.14 mmol/L (-5.6 mg/dL), P = 0.05]. The change in serum LDL cholesterol concentration was -0.26 mmol/L (-10 mg/dL), with a 95% confidence interval of -0.12 to -0.41. Serum HDL and triglyceride concentrations showed no change. These results, although based on fewer than 250 patients, suggest that T4 therapy in individuals with mild thyroid failure lowers mean serum total and LDL cholesterol concentrations. The reduction in serum total cholesterol may be larger in individuals with higher pretreatment cholesterol levels and in hypothyroid individuals taking suboptimal T4 doses. There do not seem to be significant effects of T4 on serum HDL or triglyceride concentrations.

When to treat mild hypothyroidism

The availability and wide acceptance of TSH assays for primary assessment of thyroid function has led to the recognition that mild thyroid hormone deficiency is characterized by elevation of the serum TSH concentration despite a normal free thyroxine level. Other conditions can also cause isolated serum TSH elevation, and these conditions can be distinguished from mild thyroid failure usually based-on clinical and circumstantial observations alone. Thyroxine treatment of patients with mild hypothyroidism has been shown in most, but not all, clinical trials to lower atherogenic lipid levels and relieve certain somatic and neuropsychiatric symptoms. Such treatment also prevents the progression to overt hypothyroidism, which is particularly likely in patients who are older, who have circulating thyroid autoantibodies, or who have a serum TSH greater than 10 mU/L. After the optimal thyroxine dose has been defined, long-term monitoring of patients with an annual clinical evaluation and serum TSH measurement is appropriate. The high prevalence of mild hypothyroidism, particularly in older women, and its subtle clinical presentation have led some authorities to recommend a low threshold for case-finding or routine population screening for the disorder.