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23-02-2006 | Thyroid | Article

Subclinical thyroid disease may elevate cardiovascular risk


Free abstract

Turkish research reveals that in addition to subclinical hyperthyroidism, subclinical hypothyroidism may be a risk factor for cardiovascular disease.

Although it is known that subclinical hyperthyroidism may increase a person's risk of developing cardiovascular disease, to date there are no studies examining coagulation and fibrinolytic status in patients with this condition. Moreover, the influence of subclinical hypothyroidism on such risk is controversial.

To investigate, Cihangir Erem, from Karadeniz Technical University in Trabzon, Turkey, evaluated the relationships between serum lipid profiles, thyroid hormones and hemostatic parameters in 30 patients with subclinical hypothyroidism and 20 individuals with subclinical hyperthyroidism, as well as 20 euthyroid control individuals.

Compared with control participants, total cholesterol (TC) and factor X (FX) activity was significantly increased in patients with subclinical hyperthyroidism, and participants with SHypo showed significantly elevated TC and low-density lipoprotein cholesterol levels.

In addition, in individuals with subclinical hyperthyroidism, serum thyroid stimulating hormone (TSH) levels were positively correlated with FX activity, and inversely correlated with tissue plasminogen activator inhibitor-1 levels.

Patients with subclinical hyperthyroidism who had high serum TC levels were also significantly more likely to have low plasma activities of clotting factors V, VII, VIII, IX, X, and von Willebrand factor, but high levels of plasma fibrinogen levels, than those with low TC levels.

Furthermore, in individuals with subclinical hypothyroidism, serum triglyceride levels were positively correlated with plasma fibrinogen levels, serum TSH levels, plasma activities of factors V, VII, and X, and negatively correlated with plasma fibrinogen levels.

Patients with subclinical hypothyroidism were also more likely to have high levels of factors V and X, but low levels of plasminogen activator if they had high serum TC levels. Finally, serum high-density lipoprotein cholesterol levels were inversely related to factor VII activity.

Commenting on his findings, Erem stated that increased factor X activity in patients with subclinical hyperthyroidism may "represent a potential hypercoagulable state, which might augment the already existing risk for atherosclerotic complications."

He continued: "Also, subclinical hypothyroidism patients exhibit a more atherogenic lipid profile compared with healthy individuals. Therefore, subclinical hypothyroidism is also associated with an increased risk of cardiovascular disease.

"However, thyroid hormones may play a role at different levels of the complex hemostatic system in subclinical thyroid disease," he concludes.