The Link Between Thyroid Disease and Cholesterol

Thyroid disease and high cholesterol are closely connected
Anyone who has a high cholesterol level should have their thyroid checked. GIPhotoStock/Getty

The link between thyroid disease and high cholesterol is well established. Anyone who has been diagnosed with lipid problems should have their thyroid checked, as treatment for a thyroid issue may be the key to cholesterol management. What's less well-known is that cholesterol drugs may affect thyroid disease as well. While some negatively affect the absorption of hypothyroidism drugs, one category of lipid-lowering medications (statins) may reduce the risk of thyroid eye disease in people with Graves' disease/hyperthyroidism.

The Power of the Thyroid Gland

The thyroid gland can be thought of as a master regulator of the body. Among the roles thyroid hormones play, they modulate the metabolism of lipids (such as cholesterol) by stimulating their mobilization and breakdown, and aid in the synthesis of fatty acids in the liver.

Hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid), therefore, can have unique effects on your cholesterol profile. For some people, these managing these effects may be the key to getting abnormal lipids under control.

Hypothyroidism and Hyperlipidemia

People with hypothyroidism who have a TSH between 5 mIU/L and 10 mIU/l have a significantly higher total cholesterol and LDL level than those who do not have thyroid disease. Lipid abnormalities are usually worse with primary hypothyroidism (hypothyroidism due to lack of function of the thyroid gland) than with secondary hypothyroidism (hypothyroidism due to a lack of pituitary hormones that stimulate the thyroid gland).

The lipid abnormalities seen with hypothyroidism are thought to be primarily related to a reduction in LDL receptor activity, with other effects related to lipid metabolism as well.

Thyroid replacement with levothyroxine is usually used to treat hypothyroidism (or simply a low level of thyroid hormone) and may, for some people, be all that is needed to get cholesterol levels in check.

Subclinical/Borderline Hypothyroidism, Lipids, and Heart Disease

According to a 2017 study, even subclinical (borderline) hypothyroidism is associated with lipid abnormalities, and treatment with levothyroxine has clear benefits on both LDL and total cholesterol levels in these cases as well.

Hyperthyroidism and Lipids

While, in general, it's better to have lower LDL and total cholesterol levels, there are times when a low cholesterol may not be good. An unexpected improvement in these measures may actually herald the onset of hyperthyroidism—a condition involving excess levels of thyroid hormone. If undetected and untreated, this thyroid disease can lead to complications such as eye disease, osteoporosis, atrial fibrillation (and potentially strokes or heart failure), and thyroid storm.

Hyperthyroidism is treated by reducing the level of thyroid hormone in the body, whether by medications, radioactive ablation of the thyroid gland, or surgery.

Interestingly, while hyperthyroidism may lead to low cholesterol levels, high cholesterol appears to be a risk factor for the development of Graves' disease—a particular type of hyperthyroidism.

Missed Opportunities for Cholesterol Treatment

A lipid panel is a test most doctors use to evaluate cholesterol abnormalities and is recommended for everyone beginning at age 20 (or earlier if there's a family history or other risk factors). This panel tests total cholesterol, LDL ("bad" cholesterol), HDL ("good cholesterol" or essentially the molecule that removes LDL from the body), and triglycerides.

If LDL or triglycerides are elevated, cholesterol medications may be needed, but the level at which this is recommended depends on several factors, including other risk factors for heart disease. For example, one of the statins may be recommended for a person with an LDL of 100 to reduce heart disease if other risk factors are present.

But, given the above, the presence of thyroid disease must also be considered. Unfortunately, many people have undiagnosed hypothyroidism, and far too few doctors are checking people with high cholesterol for thyroid disease.

Treating the Symptom, Not the Cause

Rather than following a treatment plan that incorporates levothyroxine, it appears that many people whose high cholesterol levels might be resolved by treatment of their thyroid disease alone are solely using cholesterol-lowering medications.

Complications

Abnormal lipids due to hypothyroidism can increase the risk of heart disease (atherosclerosis, coronary artery disease, stroke, peripheral artery disease) and potentially, mortality. Even subclinical or borderline hypothyroidism is associated with an elevated risk of heart disease as well as the risk of death from all causes combined.

While the combination of hypothyroidism and elevated cholesterol is clearly linked with heart disease, a 2018 study found that subclinical hypothyroidism alone is associated with an increased risk of cardiovascular disease as well as all-cause mortality. Some conditions associated with untreated subclinical hypothyroidism include coronary artery disease, cerebrovascular disease (such as strokes), peripheral artery disease, dilated cardiomyopathy, heart failure, atrial fibrillation, blood clots (deep venous thrombosis and pulmonary emboli), and chronic kidney disease.

Hypothyroidism Treatment's Effect on Lipids

In a large 2014 study published in JAMA Internal Medicine, 60 percent of people with a new diagnosis of hypothyroidism and hyperlipidemia had a resolution of their elevated cholesterol levels once their thyroid function was restored. Of those who were treated with levothyroxine, 75 percent did not need lipid-lowering medications within a year of hypothyroidism treatment. This percentage may be higher yet, considering that not everyone in the study had their cholesterol levels rechecked after the restoration of their thyroid function.

From the effects of thyroid replacement on lipids, it can be deduced that the treatment of hypothyroidism most likely lowers heart disease risk, but there is more evidence this is true as well, as levothyroxine has been shown to have positive effects on intimal thickness of the carotid artery (an indirect measure of heart disease risk).

Due to this evidence, professional societies such as the American Association of Clinical Endocrinologists have made recommendations to all physicians who care for people with lipid abnormalities.

Anyone who has a new diagnosis of hyperlipidemia should be screened for hypothyroidism before lipid-lowering medications are recommended. If a diagnosis of hypothyroidism is made, people should be monitored to see if levothyroxine therapy improves cholesterol levels.

In some instances, cholesterol levels will remain elevated despite treatment, and if lifestyle measures such as diet, weight loss, and exercise are not effective, cholesterol-lowering medications may then be considered.

Of note, levothyroxine appears to enhance the effectiveness of statins, ezetimibe, and PCSK9 inhibitors—all options for lowering lipid levels.

Cholesterol Medications and Thyroid Disease

Just as thyroid medications may affect cholesterol, cholesterol medications may have effects on thyroid disease or thyroid medications. In order to discuss these varying effects, it's helpful to look at individual classes of cholesterol/hyperlipidemia medications that are available and be aware of the guidelines for who should be treated.

Lipid-Lowering Medications

There are several categories of medications for hyperlipidemia with different indications. For example, some work primarily by lowering LDL, whereas others are most effective at lowering triglycerides or increasing HDL cholesterol. While there are many drugs that can lower cholesterol levels, the primary reason to do so is to lower the risk of complications such as heart disease, and available medications vary in their effect.

One of the more common interactions is in the absorption of levothyroxine (thyroid replacement therapy) in people with hypothyroidism. If you are taking these medications, your doctor will talk about how to properly take your thyroid drugs to avoid interactions. For example, some cholesterol medications may be taken an hour after taking levothyroxine, whereas others should not be taken for at least 3 hours or 4 hours.

Statins

Statins are considered the primary choice for lowering LDL levels and include:

  • Lipitor (atorvastatin)
  • Lescol (fluvastatin)
  • Mevacor, Altoprev (lovastatin)
  • Pravachol (pravastatin)
  • Crestor (rosuvastatin calcium)
  • Zocor (simvastatin)

The most common side effects of statins include muscle aches (myalgias). Muscle pain is common (and occurs in around 10 percent of people), but inflammation of muscle (statin myopathy) is less common.

Effect on hypothyroidism: People who have hypothyroidism are more likely to experience muscle pain on these drugs than people without thyroid disease. The incidence of muscle pain is higher with Zocor, and lower with Pravachol and Lescol.

Effect on hyperthyroidism: A 2018 study found that treating high cholesterol with statin medications reduced the risk of Grave's orbitopathy (eye symptoms such as bulging and more).

Statin Combinations

There are also combination medications that contain a statin and another cholesterol-lowering drug. These include:

  • Advicor (lovastatin and niacin)
  • Vytorin (simvastatin and ezetimibe)

Ezetimibe (found in Vytorin) works by blocking the absorption of cholesterol from the intestine but has a controversial history. Like statins, it may cause muscle pain.

Fibrates

Fibrates are usually recommended for people who have high triglyceride levels. and also increase HDL. These include:

  • Lopid (gemfibrozil)
  • Tricor (fenofibrate)

Niacin (Nicotinic Acid)

Like fibrates, niacin is usually used to lower triglycerides and/or raise HDL levels. It is available over-the-counter, but should be taken only under the guidance of a physician. The side effects of niacin can include flushing, hot flashes, and palpitations.

Effect on thyroid disease: The very common side effects of niacin closely mimic the symptoms of hyperthyroidism. This can be important for those living with hyperthyroidism as well as those with hypothyroidism (it may be difficult to determine if these effects are due to niacin or due to a dose of levothyroxine that is too high).

Bile Acid Resins

Bile acid resins or sequestrants reduce LDL levels by forcing the liver to clear cholesterol. Drugs in this category include:

  • Questran (cholestyramine)
  • Colestid (colestipol)
  • Welchol (colesevelam)

Effect on hypothyroidism: Bile acid resins may bind to levothyroxine preventing its absorption, and may need to be taken at least 3 hours to 4 hours after a dose of levothyroxine.

PCSK9 Inhibitors

PCSK9 inhibitors appear to lower LDL levels at least as much as statins if not more, but it's not yet known if this translates to a lower risk of heart disease. Drugs include:

  • Repatha (evolocumab)
  • Praluent (alirocumab)

Effect on hypothyroidism: As with statins, PCSK9 inhibitors may cause muscle pain, and it's noted that people with hypothyroidism on statins are more likely to experience this side effect than those without thyroid disease.

Non-Medication Ways to Lower Cholesterol

For those who have lipid levels that are elevated but not high enough to require medications (and also for those for who medications are recommended), there are some simple tips to lower your LDL.

Diet

The role of diet has changed significantly in recent years, and the very low-fat diets of the past have gone by the wayside. Despite these changes, increasing fiber in the diet, as well as using "healthy oils" such as olive oil (instead of corn oil, vegetable oil, etc.) may be beneficial. As a general diet, the Mediterranean diet may reduce cholesterol and has positive benefits with regard to heart health.

Weight Loss

Dietary changes could be very helpful if they lead to weight reduction in people who are overweight. It's been shown that even a 10-pound weight loss may reduce LDL levels up to 8 percent.

Exercise

While exercise does not affect LDL levels to a significant degree (unless weight loss occurs), it can increase HDL levels. Since HDL works by essentially clearing the body of LDL, this can be very helpful. In fact, doctors are often much more comfortable with people having higher LDL levels if they also have higher HDL levels. Even yoga may help lower cholesterol levels.

Quitting Smoking

Quitting smoking is one of the easiest (for those who smoke) ways to reduce atherosclerosis, and the risk of heart disease, strokes, peripheral artery disease, and much more. Since the primary concern with abnormal lipids is the increased risk of heart disease, smoking cessation is an essential part of managing elevated cholesterol levels.

Lifestyle Measures for High Cholesterol and Thyroid Disease

Proper treatment of hypothyroidism is important, as low thyroid hormone levels lead to fatigue, and subsequently, less interest in exercise. Of note is that some foods (goitrogens), while healthy on their own, can have anti-thyroid effects. If you have hypothyroidism and adopt a healthy diet to control your cholesterol, it's important to limit or space out these foods in your diet. There are other dietary recommendations for people with thyroid disease that are helpful for those who are trying to lose weight, or just wish to feel as good as possible while living with thyroid disease.

A Word From Verywell

If you have been newly diagnosed with high cholesterol or other lipid abnormalities and do not have known thyroid disease, be sure to have your doctor screen you for hypothyroidism right away, and especially before taking any cholesterol medications. This can be done with a simple blood test. You may need to be your own advocate and request the test, since the JAMA study noted above found that only around 50 percent of people with newly diagnosed hyperlipidemia were adequately screened for thyroid disease.

Hypothyroidism is considered to be vastly underdiagnosed, and it's likely that many people are now being treated with cholesterol drugs (and coping with the side effects), when their cholesterol might well be normal with proper treatment of their thyroid condition. Even borderline or subclinical hypothyroidism is of concern. On the other side of the spectrum, if your cholesterol levels are suddenly improving (for no apparent reason), blood tests should be done to check for hyperthyroidism.

If you have thyroid disease, either hypothyroidism or hyperthyroidism, knowing how cholesterol levels and thyroid function relate is important. Optimal treatment of hypothyroidism with levothyroxine (or with combination T4/T3 therapy or natural thyroid) is important in lowering cholesterol levels and reducing the risk of heart disease. For those who have Grave's disease/hyperthyroidism, treating elevated cholesterol may reduce the risk of developing thyroid eye disease.

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