Abnormal thyroid activity can change serum lipids and other risk factors for cardiovascular disease. Low thyroid activity (hypothyroidism) can raise serum lipids, and treatment can return them to normal. However, hyperthyroidism can be associated with low serum cholesterol also. Thyroid hormone increases cholesterol production and insulin resistance. People with high anti-thyroid antibodies can have high cholesterol levels.
TSH (thyroid stimulating hormone) levels help diagnose mild hypothyroidism. Even when TSH levels are in normal limits, increasing levels of TSH are associated with increased cholesterol, LDL cholesterol, and triglycerides. Increased TSH levels correlate with increased BMI (body mass index) and being overweight, especially in non-smokers.
Before treatment of a patient for high lipids, a total evaluation of thyroid function is necessary to rule out thyroid disease. Patients started on statin drug therapy who had undiagnosed hypothyroidism had significantly higher creatinine kinase (CK) levels, consistent with muscle inflammation. Statins are known to raise CK levels related to muscle fiber damage. It is important to evaluate thyroid function before starting statin therapy. Hypothyroid patients seem to be at increased risk of developing muscle complications with statin therapy.
Subclinical hypothyroidism (SH) causes increased TSH levels with normal T3 and T4. SH can develop into overt hypothyroidism, and is more common than overt hypothyroidism. Hypothyroidism is associated with hypertension and metabolic syndrome.
Treatment of hypothyroidism improves the abnormalities of fat metabolism in 4-6 weeks. There is not a clear agreement on the treatment of SH. However, a conservative approach would be to treat those with TSH levels over 10 mIU/L with thyroxin substitution, especially if they have higher cholesterol levels. Treatment of hyperthyroidism clearly returns lipid factors toward normal.
CONCLUSION: The various changes in serum lipids seen in thyroid disease make it important to thoroughly evaluate thyroid function before starting drugs for lowering lipids. This is especially important in those with high creatinine kinase (CK) levels.
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