High cholesterol is a condition where there are unhealthy levels of cholesterol in the blood. While high cholesterol is often caused by lifestyle factors like diet and exercise, it can also be caused by underlying health conditions. One organ that plays a major role in regulating cholesterol levels is the liver. When the liver is not functioning properly, it can lead to disrupted cholesterol production and metabolism, resulting in high cholesterol levels.
How does the liver regulate cholesterol?
The liver plays a central role in regulating cholesterol in the body. It processes cholesterol by:
- Producing cholesterol – The liver produces and secretes cholesterol into the bloodstream.
- Converting cholesterol into bile acids – The liver turns cholesterol into bile acids which help digest fats. This is one way to eliminate excess cholesterol from the body.
- Regulating LDL receptors – The liver controls LDL receptors which remove LDL (bad) cholesterol from the bloodstream.
When the liver is damaged or diseased, these important cholesterol regulating functions can become impaired. This allows cholesterol levels to rise unchecked, resulting in hypercholesterolemia (high cholesterol).
Liver diseases that commonly cause high cholesterol
There are several common liver conditions that disrupt normal cholesterol metabolism and frequently cause high cholesterol levels. These include:
1. Nonalcoholic fatty liver disease (NAFLD)
NAFLD is an umbrella term for a range of liver conditions caused by a buildup of fat in liver cells. It is the most common chronic liver disease in developed countries, affecting up to 30% of adults.
NAFLD disrupts normal fat metabolism in the liver, including cholesterol metabolism. Studies show over half of people with NAFLD have high cholesterol.
2. Alcoholic liver disease
Drinking excessive amounts of alcohol over many years can cause liver inflammation and damage. This is known as alcoholic liver disease.
Alcohol impacts how the liver regulates cholesterol. It reduces bile acid production and secretion which allows blood cholesterol levels to rise.
Up to 44% of people with alcoholic cirrhosis have high cholesterol. The more severe the liver damage, the greater the cholesterol increase.
3. Viral hepatitis
Viral hepatitis refers to liver inflammation caused by hepatitis viruses. The most common types are hepatitis B and hepatitis C.
In chronic viral hepatitis, the liver slowly becomes damaged and scarred over time. This impairs its ability to regulate lipids, allowing cholesterol to build up in the blood.
Studies show 16-37% of people with chronic hepatitis C infection have high cholesterol. For hepatitis B, the rate is 28-47%.
4. Cirrhosis
Cirrhosis occurs when healthy liver tissue is replaced with scar tissue, often due to chronic liver disease. This extensive scarring prevents the liver from functioning normally.
Any type of chronic liver disease can eventually lead to cirrhosis. Up to 60% of people with cirrhosis have elevated cholesterol levels.
5. Primary biliary cholangitis
Primary biliary cholangitis (PBC) is an autoimmune disease where the bile ducts in the liver become damaged and inflamed. This disrupts the flow of bile.
Impaired bile flow affects fat absorption and elimination, including cholesterol. Up to 52% of people with PBC have high cholesterol.
Other liver conditions linked to high cholesterol
While less common, there are some other liver disorders also associated with high cholesterol:
- Hemochromatosis – An iron overload disorder that can damage the liver.
- Wilson’s disease – Buildup of copper in the liver and other tissues.
- Primary sclerosing cholangitis – Inflammation and scarring of the bile ducts.
- Gilbert’s syndrome – Mild liver disorder causing unconjugated hyperbilirubinemia.
Mechanisms – how liver disease raises cholesterol
There are a few key mechanisms by which liver dysfunction contributes to high cholesterol levels:
1. Reduced LDL receptor function
LDL receptors on liver cells remove LDL cholesterol from the bloodstream. Liver damage impairs LDL receptor function, slowing LDL clearance.
2. Decreased bile acid synthesis
Damaged liver cells produce less bile acid from cholesterol. This reduces cholesterol excretion from the body.
3. Increased HMG-CoA reductase activity
HMG-CoA reductase is the enzyme involved in cholesterol production. Liver disease enhances reductase activity, increasing cholesterol synthesis.
4. Impaired cholesterol conversion to bile
Diseased liver cells cannot efficiently convert cholesterol into bile acids for excretion.
5. Changes in lipoprotein metabolism
Liver disease alters the production and makeup of lipoproteins that transport cholesterol in the blood.
Diagnosis
High cholesterol can be detected via a simple blood test. More extensive testing is required to diagnose any underlying liver disease that may be causing elevated cholesterol levels. This may include:
- Liver function blood tests – Checks levels of liver enzymes and proteins.
- Imaging tests – CT scan, MRI, or ultrasound to examine the liver.
- Liver biopsy – Removal of a small liver tissue sample for examination under a microscope.
Once a specific liver disorder is diagnosed, the cause of high cholesterol becomes clear. Ongoing monitoring of cholesterol and liver health is important.
Treatment
Treatment focuses on both lowering cholesterol levels and managing the underlying liver problem. This dual approach is key to reducing cardiovascular risk and supporting liver health. Treatment may include:
- Cholesterol-lowering medications – Statins, fibrates, niacin, bile acid resins.
- Lifestyle changes – Diet, exercise, smoking and alcohol cessation.
- Treating the liver condition – Medications, surgery, or liver transplant if cirrhosis.
Treatment goals include reducing LDL cholesterol to under 100 mg/dL and total cholesterol under 200 mg/dL, though optimal targets depend on overall cardiovascular risk.
The bottom line
Liver disease disrupts cholesterol regulation leading to high blood cholesterol levels. Common liver conditions like NAFLD, hepatitis, and cirrhosis are linked to elevated cholesterol. Diagnosing and properly treating the underlying liver problem, along with cholesterol lowering therapy, provides the best outcome.
Frequently Asked Questions
How does the liver regulate cholesterol?
The liver helps regulate cholesterol levels by producing cholesterol, converting cholesterol into bile acids, and controlling LDL receptors that remove LDL cholesterol from the bloodstream. Liver damage impairs these key functions.
What percentage of people with cirrhosis have high cholesterol?
Studies show around 60% of people with cirrhosis of any cause have elevated cholesterol levels. The more advanced the cirrhosis, the higher the likelihood of increased cholesterol.
Does hepatitis C cause high cholesterol?
Yes, chronic hepatitis C infection is associated with high cholesterol in 16-37% of cases. Hepatitis C causes progressive liver inflammation and scarring that disrupts normal cholesterol regulation.
Can fatty liver cause increased cholesterol?
Yes, nonalcoholic fatty liver disease (NAFLD) directly impairs cholesterol metabolism. Over 50% of people with NAFLD have abnormally high cholesterol levels. Treating the underlying fatty liver is key to improving cholesterol.
How do you treat high cholesterol caused by liver disease?
Treatment involves a two-pronged approach – lowering cholesterol levels with medication and lifestyle changes, as well as diagnosing and managing the liver condition causing cholesterol dysregulation. This dual treatment is important for cardiovascular and liver health.