The Link Between Your Thyroid and Your Cholesterol

Woman having her thyroid examined
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High cholesterol is a common health problem among Americans and a major contributor to heart disease.

Yet you may be surprised to learn that a poor diet and insufficient exercise are not always the culprits behind a person's high cholesterol. In fact, an easily treatable and secondary cause of high cholesterol is an underactive thyroid (called hypothyroidism).

Understanding Cholesterol

Cholesterol is a waxy substance found in animal foods, like meat and full-fat dairy products. Cholesterol is also manufactured naturally in your liver where it's transported by fat-carrying proteins in the blood.

There are two types of cholesterol— low-density lipoprotein (LDL) is your "bad" cholesterol and high-density lipoprotein (HDL) is your "good" cholesterol. 

Bad Cholesterol

The reason LDL is "bad" is that as it travels through your bloodstream, it may form a hard deposit in the walls of arteries. Eventually, these fatty deposits make the arteries narrow and less flexible (this condition is called atherosclerosis).

Then, if a clot develops and blocks one of these narrowed arteries, blood flow cannot reach vital organs like your heart and brain; so, as a result, a heart attack or stroke may occur.

Good Cholesterol

HDL is considered "good" because it carries some of your LDL cholesterol away from your arteries, back to your liver where it can be broken down. This is why an elevated HDL cholesterol may protect a person from having a heart attack or stroke.

On the flip side, low HDL levels increase a person's risk of having a heart attack and/or stroke. 

Understanding the Link

The thyroid, a butterfly-shaped gland located behind and below your Adam's Apple, produces hormones that help regulate your metabolism and facilitate the delivery of oxygen and energy to cells, tissues, and organs.

In addition to several other important metabolic functions in your body, when your thyroid produces too little hormone (called hypothyroidism), your ability to process cholesterol may also be impaired. More specifically, hypothyroidism is associated with elevated LDL and total cholesterol levels.

Due to the fact that hypothyroidism is present in up to 13 percent of people with high cholesterol, professional societies like the National Cholesterol Education Program, American Association of Clinical Endocrinologists, and the American Thyroid Association all recommend screening for hypothyroidism in people who are newly diagnosed with high cholesterol (before starting them on a cholesterol-lowering medication).

This is because cholesterol levels may improve with treatment of the hypothyroidism. In fact, according to a study in JAMA Internal Medicine, only 25 percent of people with high cholesterol and hypothyroidism were prescribed a cholesterol-lowering medication within one year of starting levothyroxine (a thyroid hormone replacement medication). 

Screening for Hypothyroidism

Unfortunately, though, despite the strong connection between high cholesterol and hypothyroidism, about half of people newly diagnosed with high cholesterol are still not screened for thyroid dysfunction—and it's unclear why.

It's possible that doctors are not screening for thyroid dysfunction because a person does not report any other symptoms of hypothyroidism (for example, constipation, hair loss, or depression). It's important to understand, however, that a high cholesterol alone is enough to screen for an underactive thyroid gland, especially considering most hypothyroid symptoms (if present) are nonspecific, so easily attributed to other factors. 

Hopefully, with more awareness of these guidelines, this will change. 

A Word From Verywell

If you or a loved one is newly diagnosed with high cholesterol, it's sensible to remind your doctor to screen you for hypothyroidism. This can be easily done with a blood test that measures your thyroid-stimulating hormone, or TSH.

If your TSH is found to be elevated (and you are diagnosed with hypothyroidism), taking thyroid hormone replacement will not only make you feel better, but it will also benefit your heart health.

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Article Sources
  • American Heart Association. (2017). About Cholesterol.
  • Garber JR et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract. 2012 Nov-Dec;18(6):988-1028.
  • Tagami T et al. Multi-center study on the prevalence of hypothyroidism in patients with hypercholesterolemia. Endocr J. 2011;58(6):449-57.
  • Willard DL, Leung AM, Pearce EN. Thyroid function testing in patients with newly diagnosed hyperlipidemia. JAMA Intern Med. 2014 Feb 1;174(2):287-89.