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Hypothyroidism is a medical condition characterized by an underactive thyroid gland. Because of this, the thyroid gland cannot produce sufficient thyroid hormone. Thyroid hormone is crucial in regulating various metabolic processes, including lipid metabolism. People with hypothyroidism often experience changes in their lipid profile, resulting in hyperlipidemia, defined as high cholesterol and triglyceride levels. In fact, over 90% of those with overt hypothyroidism have hyperlipidemia.
This raises a question: how and why does hypothyroidism affect your lipid levels? Keep reading to learn more.
Lipids (fats) are essential for various functions in the body, such as building cells, producing energy, and making certain hormones. But, when you have too much fat in your blood, it is called hyperlipidemia. And hyperlipidemia puts you at risk for health-related complications.
Types of lipids
Most people are familiar with the two main lipids found in the blood: cholesterol and triglycerides. Our bodies make cholesterol in the liver. The intestines also absorb cholesterol from the food you eat.
Cholesterol is transported throughout the body on lipoproteins. The two most common types of cholesterol are:
- Low-density lipoprotein cholesterol (LDL-C), nicknamed “bad” cholesterol
- High-density lipoprotein cholesterol (HDL-C), referred to as “good” cholesterol
A high LDL-C isn’t good as it can cause plaque formation in the arteries. As a result, arteries become narrow, limiting the amount of blood flow throughout the body. Narrowed arteries put individuals with a high LDL-C at increased risk of heart-related events such as a stroke or heart attack. Having a high triglyceride level with a high LDL-C level further increases the risk of heart problems.
In contrast, having a high HDL-C level is good. HDL-C removes fat from your blood and brings it back to the liver. The liver breaks down the excessive fat and removes it from the body. Because of this, a high level of HDL-C helps reduce your risk of heart disease.
Those with hyperlipidemia don’t usually have noticeable symptoms, making blood tests an essential part of diagnosing it. A lipid panel requires a blood draw and generally includes the following:
- Total cholesterol
- LDL-C
- HDL-C
- Triglycerides
As the name suggests, total cholesterol is the total amount of cholesterol in the blood. This number is based on your HDL-C, LDL-C, and triglyceride numbers.
As mentioned, thyroid hormones thyroxine (T4) and triiodothyronine (T3) influence lipid metabolism. Here’s how.
Thyroid hormone impacts all aspects of lipid metabolism. Without enough thyroid hormone,
- The amount of cholesterol the liver makes decreases.
- LDL-C builds up in the blood.
- There is an increase in cholesterol absorption from the intestines.
Despite the liver’s reduced cholesterol synthesis, LDL-C still increases when thyroid hormone is lacking. Furthermore, low thyroid hormone levels can lower HDL-C and elevate triglycerides. The triglyceride increase is due to the body’s inability to break them down effectively. Remember, a high LDL-C and triglyceride level with a low HDL-C translates to an increased risk of heart-related events.
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Thyroid-stimulating hormone (TSH) is often used as a marker to assess thyroid function. Its primary role is to signal the thyroid gland to make and release thyroid hormone. A high TSH level means the thyroid is underactive, while a low TSH level indicates an overactive thyroid.
Studies show a chronic increase in TSH and total cholesterol, LDL-C, and triglyceride. But the opposite is true for HDL-C - it decreases. These lipid changes occur not only in individuals with overt hypothyroidism but also in those with a TSH value within the upper range of normal. For instance, if an individual’s TSH increases from 3 mIU/L to 4 mIU/L, a level still within the normal range for adults, LDL-C and triglycerides will increase.
An acute change in TSH, causing short-term overt hypothyroidism, also affects the lipid panel. In this situation, all lipid values increase, even HDL-C. This evidence comes from studies examining lipid profiles in post-thyroidectomy individuals waiting for their subsequent treatment.
In those with overt hypothyroidism, LDL-C and total cholesterol increase on average by about 30%. The greater the TSH value, the more adverse the lipid panel becomes. Those with a TSH level greater than 10 mIU/L have the most unfavorable lipid profile.
Subclinical hypothyroidism and lipid changes
Subclinical hypothyroidism is a mild form of hypothyroidism that occurs in 4 to 10% of adults. It is characterized by an elevated TSH level with a normal T4 level. This differs from the changes seen in those with overt hypothyroidism, who have a high TSH with a low T4 level.
Several studies have documented lipid abnormalities in individuals with subclinical hypothyroidism. The most consistent abnormalities are elevated total cholesterol and LDL-C. But, the effect subclinical hypothyroidism has on triglycerides and HDL-C varies depending on the study. For instance, some studies suggest no changes to HDL-C levels, while others show a significant decrease.
Interestingly, those with a high triglyceride level tend to have higher TSH levels, putting them at risk for developing subclinical hypothyroidism. One study calculated this risk to be as high as 35%! Researchers believe this is because a high triglyceride level causes lipotoxicity. Lipotoxicity is the build-up of fat in non-fat tissues such as the heart or kidney. As a result, experts believe lipotoxicity affects the structure and function of the thyroid, resulting in thyroid dysfunction.
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The treatment of hypothyroidism generally involves taking thyroid hormone replacement medication. These medications mimic the structure and actions of your natural thyroid hormones, T4 or T3. As thyroid hormone levels return to normal, the TSH level will decrease.
Managing thyroid hormone levels improves lipid abnormalities in both subclinical and overt hypothyroidism. But the degree of improvement varies.
When treated with levothyroxine, the synthetic form of T4, those with overt hypothyroidism saw a significant improvement in their lipid levels. A 2020 study reported that, on average,
- Total cholesterol decreased by 58 mg/dL
- LDL-C dropped by 41 mg/dL
- Triglycerides fell by 7 mg/dL
- HDL-C lowered by 4 mg/dL
For individuals with subclinical hypothyroidism, levothyroxine treatment also improved their lipid profile, but to a lesser extent. The same 2020 study showed decreased total cholesterol and LDL-C by 12 mg/dL and 11 mg/dl, respectively. There was no significant change in HDL-C levels in this population.
These findings show the importance of thyroid hormone replacement therapy in managing lipid abnormalities in patients with hypothyroidism. Yet not everyone with subclinical hypothyroidism takes thyroid hormone medication - a highly debated topic. Thyroid guidelines also recommend against taking thyroid hormone medication to correct hyperlipidemia in the absence of a thyroid disorder.
For those with other reasons for hyperlipidemia, such as genetics, correcting thyroid hormone levels won’t fix your lipid abnormalities. You may need to manage hyperlipidemia in different ways as well, such as:
- Taking an anti-lipid medication such as atorvastatin (Lipitor) or simvastatin (Zocor)
- Increasing physical activity
- Limiting high-cholesterol foods like deep-fried and processed foods
- Smoking cessation
Regular monitoring of lipid and thyroid hormone levels allows for early detection of abnormalities. Addressing these abnormalities early in the process can help prevent complications such as a stroke or heart attack. Your provider will determine what regular monitoring looks like for you. Everyone has a different monitoring schedule based on their medical history, certain risk factors, and symptoms.
If your provider recommends monitoring your thyroid function, Paloma Health offers an at-home testing kit for your convenience. Our testing kit measures TSH, T4, and T3 levels and checks for the presence of thyroid antibodies. Additionally, you can choose to include a vitamin D level, as deficiencies in vitamin D are common in those with hypothyroidism.
Utilizing Paloma’s comprehensive testing kit provides a convenient way to stay on top of your health. Order your kit today!
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