What is Cholesterol in the Body?
Cholesterol is a fat-like but waxy substance also called a lipid. Your body uses cholesterol to make cell membranes and maintain their structure and function. In the right amounts, cholesterol can be good for you, as cholesterol also helps produce hormones, vitamin D, and digestive substances you need to break down food.
Cholesterol is found in two sources: from animal-sourced foods like eggs, meat, and cheese, or from your liver. Cholesterol travels through the blood in spherical particles called lipoproteins. This is where the terms low-density lipoprotein (LDL) and high-density lipoprotein (HDL) come from. Lipoproteins are made of proteins and lipids. There are in fact, five different kinds of lipoproteins: chylomicrons (CMs), very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL).
Types of Cholesterol
- Chylomicrons carry esterified cholesterol, cholesterol absorbed by the intestinal epithelia or lining cells, and phospholipids. High levels of chylomicrons can accumulate in the liver and spleen and cause organomegaly or abnormal enlargement. It can gather in the skin and cause eruptive xanthomas where yellow bumps or papules appear on the skin’s surface. Accumulation in the retinal blood vessels can also cause lipemia retinalis where the blood vessels appear discolored and possibly affect vision.
- Very low-density lipoproteins (VLDL) transport lipids from the liver to the surrounding adipose, cardiac, and muscle tissues. High VLDL levels are associated with high-fat diets, obesity, insulin resistance, and metabolic syndrome.
- Intermediate-density lipoproteins (IDL) are a lipoprotein’s form during the transition between VLDL to LDL. It is a significant risk marker for coronary heart disease.
- Low-density lipoprotein or LDL is sometimes called “bad” cholesterol. It is a fat that travels in the blood and moves cholesterol to parts of the body when it is needed for repairing the cells. LDL also stores cholesterol in the artery walls. The body needs LDL for absorbing dietary cholesterol and other lipids from the small intestine and moving it between the liver and surrounding tissues. At high levels, LDL will store more cholesterol in the arteries and lead to plaque buildup. High LDL increases the risk of cardiovascular disease, hypertension, and atherosclerosis.
- High-density lipoprotein or HDL is often called “good” cholesterol. HDL helps transport excess cholesterol from peripheral (surrounding) tissues and the bloodstream back to the liver. This helps reduce the risk of atherosclerosis, the build-up of fatty substances like cholesterol in the arteries that forms plaque along the artery walls. High levels of HDL have been found to decrease the risk of coronary heart disease, but can also cause endothelial lipase deficiency. If the body lacks endothelial lipase, a substance formed by the endothelial cells that line blood vessels, lymph vessels, and the heart, then lipoprotein metabolism is reduced. In other words, HDL can protect the body from cardiovascular risks but when high enough will prevent the formation of endothelial lipase and take away the cardiovascular benefit. This is where moderation is key!
Cholesterol is needed for the body to function properly, but can also be harmful in abnormal amounts. In some cases, medication is required to reduce high levels of LDL cholesterol or maintain healthy levels of HDL cholesterol. A healthy diet and exercise can also help maintain healthy levels of cholesterol.
The Link Between Thyroid Disorders and Cholesterol
Your thyroid gland is responsible for hormone production for processes such as metabolism, growth, and development. Hormones enter the bloodstream and respond to your body’s needs. Some of these hormones are needed for regulating cholesterol or lipid metabolism in the body. Lipid metabolism is simply defined as the “use or storage of fats for energy”.
One study on patients with thyroid cancer found that when patients had low levels of thyroid-stimulating hormone or TSH (otherwise identified as subclinical hyperthyroidism), they had an increased risk of cardiovascular disease. The researchers concluded that HDL production was lower in patients with subclinical hypothyroidism.
On the other hand, in overt hypothyroidism, patients had lower levels of unesterified and esterified cholesterol, triglycerides, and phospholipids. In subclinical hyperthyroidism, they found an increase in both unesterified and esterified cholesterol transfer to HDL. Therefore, they had solid evidence to state that plasma lipid metabolism and thyroid hormones were related.
Cholesterol and Hypothyroidism
Hypothyroidism occurs when the thyroid gland doesn’t make enough thyroid hormones and causes symptoms such as fatigue, weight gain, muscle pain, menstrual complication, and slowed heart rate. With hypothyroidism, many patients experience higher levels of HDL cholesterol. This is likely due to the body having difficulty removing the excess cholesterol from the bloodstream. HDL is elevated as two enzymes regulated by the thyroid hormones experience decreased activity. These two hormones are called cholesteryl-ester transfer protein (CETP) and hepatic lipase (HL).
Many individuals with hypothyroidism are prescribed levothyroxine (LT4) as treatment. Studies have found that patients treated with LT4 had higher LDL cholesterol levels than the general population. One study found that LT4-treated patients regularly used statins, a medication that helps lower LDL cholesterol in the blood and prevent a build-up of plaque in the arteries. Despite having normal serum TSH levels, the lipid profiles of these patients indicated that they were at risk of developing hypercholesterolemia. Hypercholesterolaemia is characterized by excess levels of LDL or HDL and is a major risk factor for developing cardiovascular diseases and conditions such as coronary heart disease, peripheral arterial disease, myocardial infarction, ischemic stroke, and ischemic cardiomyopathy. Hypothyroidism is also associated with hypertriglyceridemia where there are too many triglycerides, another lipid, in the bloodstream.
Another study found that treating hypothyroidism was beneficial for decreasing cholesterol levels. Patients with overt hypothyroidism, where TSH was high and free thyroxine was low, were treated with levothyroxine and saw significant decreases in their total cholesterol levels. On the other hand, in patients with subclinical hypothyroidism, where TSH was high and free thyroxine was normal, treatment with thyroxine saw small reductions in cholesterol.
Hypothyroidism is also associated with increased levels of LDL cholesterol. With the upregulation of TSH, patients also experience hyperlipidemia or an increase in LDL and VLDL in the blood. It was found that hypothyroid individuals had an increased risk of cardiovascular disease concluding that dysfunctional thyroid hormone levels contributed to lipid metabolic disorders.
With hypothyroidism, where thyroid hormone levels decrease, patients experience fatigue and decreased levels of physical activity. Combined with an unhealthy diet and weight gain, lifestyle choices can contribute to high cholesterol levels.
Cholesterol and Hyperthyroidism
Hyperthyroidism causes the thyroid gland to produce excessive amounts of thyroid hormones. This can cause symptoms such as weight loss, irregular heartbeat, nervousness or anxiety, enlargement in the neck or goiter, and muscle weakness. Hyperthyroidism is associated with lower levels of cholesterol and triglycerides in the bloodstream. Individuals with hyperthyroidism were observed to have cardiovascular conditions such as systolic hypertension, atrial fibrillation, and other atrial arrhythmias. Treatment of overt hyperthyroidism reduced the risk of cardiovascular, neuromuscular, and neuropsychiatric conditions and diseases.
Patients treated for overt hyperthyroidism with thyroid hormone therapy saw an increase in their cholesterol levels. A study took 59,021 hyperthyroid patients and compared the incidence of myocardial infarction, stroke, and cardiovascular disease to healthy control patients. Not only did the study find that myocardial infarction and stroke were higher in hyperthyroid patients, but the study also found that hyperthyroidism can accelerate atherosclerosis. Hyperthyroidism disrupts the body’s endothelial cells and thyroid autoimmunity which contributes to plaque build-up in the arteries. Moreover, those with hyperthyroidism showed worse systolic blood pressure and fasting blood sugar levels. Hyperthyroidism in the body shows low levels of TSH but high levels of free thyroxine. A Rotterdam study found that there was a positive correlation between free thyroxine and atherosclerosis and atherosclerosis events such as coronary disease and cerebrovascular disorder.
Improving Your Health
Having thyroid issues does not mean you are certain to experience severe consequences with cholesterol. You have the power to make healthier decisions and to speak with your healthcare provider to improve your health.
Making lifestyle changes can help you manage your thyroid condition and cholesterol. First, adopting a healthy diet that is rich in fruits, vegetables, and healthy fats can lower your cholesterol. Switch to whole grains and lean proteins instead of sugary baked items. Replace processed foods, saturated fats, and refined sugars with natural and organic products.
Exercise is also important. By exercising, you can improve your cardiovascular health, burn calories, reduce stress, and improve your brain function. Reducing stress levels is especially important for thyroid health as stress can release hormones and increase your cholesterol levels. Stress can elevate cholesterol, and hemoglobin concentration, and negatively alters your lipoprotein metabolism. Reduce your stress levels by meditating, trying yoga, going for regular walks, and seeking professional help to keep track of your mental health.
- Cholesterol can be sourced from animal-based foods or the liver and travels through the body in the form of lipoproteins.
- High-density lipoprotein (HDL) is considered “good” cholesterol as it helps reduce excess cholesterol in the bloodstream by sending it to the liver. In high concentrations, HDL can increase the risk of cardiovascular disease.
- Low-density lipoprotein (LDL) is considered “bad” cholesterol as it travels in the blood and gets stored in the artery walls leading to plaque buildup and increased risk of atherosclerosis.
- Hypothyroidism is associated with elevated levels of LDL and HDL in the body. Hypothyroid individuals can experience hypercholesterolemia or hypertriglyceridemia. They are at a higher risk of cardiovascular diseases such as coronary heart disease, myocardial infarction, and stroke.
- Hyperthyroidism is associated with lower levels of cholesterol and triglycerides. There is a positive correlation between free thyroxine in hyperthyroidism and atherosclerosis.
- A healthy diet, exercise, and stress management will help manage both conditions and improve thyroid health and cholesterol.