Your doctor has probably cautioned you about cholesterol, the fatty, waxy substance that circulates in your blood. Too much of the wrong type of cholesterol can clog your arteries and put you at risk for heart disease.
High cholesterol levels can stem from your diet, especially if you eat foods high in saturated fats, like red meat and butter. Sometimes, though, your thyroid gland may be to blame. Too much or too little thyroid hormone can make your cholesterol levels swing up or down.
Here’s a look at how your thyroid affects cholesterol.
Your thyroid is a butterfly-shaped gland in your neck. It produces hormones that control metabolism. Metabolism is the process your body uses to convert food and oxygen into energy. Thyroid hormones also help the heart, brain, and other organs work normally.
The pituitary gland is located at the base of the brain and directs the thyroid’s activities. When your pituitary senses that you’re low in thyroid hormone, it releases thyroid-stimulating hormone (TSH). TSH directs the thyroid gland to release more hormones.
Cholesterol is contained in each of your body’s cells. Your body uses it to make hormones and substances that help you digest food.
Cholesterol also circulates through your blood. It travels in the bloodstream in two types of packages, called lipoproteins:
- High-density lipoprotein (HDL) cholesterol is good for your heart. It helps remove cholesterol from your body and protects against heart disease.
- Low-density lipoprotein (LDL) cholesterol is bad for your heart. If LDL cholesterol levels are too high, the cholesterol can clog arteries and contribute to heart disease, heart attacks, and strokes.
The thyroid can produce too little or too many hormones sometimes.
A condition in which your thyroid is underactive is called hypothyroidism. When the thyroid is underactive, your whole body feels like it’s slowing down. You become tired, sluggish, cold, and achy.
You might get an underactive thyroid if you have the following conditions:
- Hashimoto’s thyroiditis, an autoimmune disease in which the body attacks and destroys the thyroid gland
- thyroid inflammation (thyroiditis)
Other factors that can result in an underactive thyroid include:
- removal of all or part of an overactive thyroid
- radiation for cancer or an overactive thyroid
- certain medications, such as lithium, interferon alpha, and interleukin 2
- damage to the pituitary gland from a tumor, radiation, or surgery
Hyperthyroidism is a condition that occurs when you have an overactive thyroid. When your thyroid is overactive, your body kicks into fast gear. Your heart rate speeds up, and you feel nervous and shaky.
You might get hyperthyroidism if you have:
- Graves’ disease, an immune system disorder that runs in families
- toxic nodular goiter, which involves lumps or nodules on the thyroid
- thyroid inflammation (thyroiditis)
Your body needs thyroid hormones to make cholesterol and to get rid of the cholesterol it doesn’t need. When thyroid hormone levels are low (hypothyroidism), your body doesn’t break down and remove LDL cholesterol as efficiently as usual. LDL cholesterol can then build up in your blood.
Thyroid hormone levels don’t have to be very low to increase cholesterol. Even people with mildly low thyroid levels, called subclinical hypothyroidism, can have higher than normal LDL cholesterol. A 2012 study found that high TSH levels alone can directly raise cholesterol levels, even if thyroid hormone levels aren’t low.
Hyperthyroidism has the opposite effect on cholesterol. It causes cholesterol levels to drop to abnormally low levels.
You might have an underactive thyroid gland if you notice these symptoms:
- weight gain
- slow heartbeat
- increased sensitivity to cold
- muscle aches and weakness
- dry skin
- trouble remembering or focusing
An overactive thyroid has almost the exact opposite symptoms:
If you have symptoms of a thyroid problem and your cholesterol levels are high or low, see your doctor. You’ll get blood tests to measure your level of TSH and your level of a thyroid hormone called thyroxine. These tests will help your doctor find out if your thyroid is overactive or underactive.
Taking the thyroid hormone replacement medicine levothyroxine (Levothroid, Synthroid) to treat an underactive thyroid can also help lower your cholesterol level.
When your thyroid hormone level is just marginally low, you may not need thyroid hormone replacement. Instead, your doctor might put you on a statin or other cholesterol-lowering drug.
For an overactive thyroid, your doctor will give you radioactive iodine to shrink the gland or medicines to reduce thyroid hormone production. A small number of people who can’t take antithyroid drugs may need surgery to remove most of the thyroid gland.