Lack of thyroid hormones decreases the liver’s ability to clear cholesterol from the blood, so people with hypothyroidism tend to have high LDL (“bad”) cholesterol and high triglycerides. This may be one reason why hypothyroidism is associated with increased risk of atherosclerosis and heart attacks in many studies.
If you have high LDL cholesterol, your doctor should check to see if you have hypothyroidism, especially if you are a woman over 60. If so, it makes sense to treat the thyroid condition first, rather than take cholesterol-lowering medication.
Treating hypothyroidism usually results in a significant reduction in cholesterol. However, studies on the effect of treatment of subclinical hypothyroidism on cardiovascular outcomes have had inconsistent results.