Like cholesterol, triglycerides are common types of fats (lipids) that are essential for good health when present in normal amounts. They account for about 95 percent of the body’s fatty tissue. Triglycerides are present in food as well as manufactured by the body.

Abnormally high triglyceride levels are associated with a number of diseases and conditions, such as cirrhosis (a disease of the liver), underactive thyroid gland(hypothyroidism), diabetes and pancreatitis (inflammation of the pancreas).

High triglyceride levels are also associated with known risk factors for heart disease, such as low levels of HDL (“good”) cholesterol, high levels of LDL ("bad") cholesterol and obesity. Additionally, triglycerides may contribute to a type of thickening of artery walls, a physical change believed to be a predictor of hardening of the arteries (atherosclerosis). Researchers are continuing to investigate how triglycerides affect cardiovascular health.

At the very least, high triglyceride levels are a warning sign that a patient’s heart health may be at risk. In response, physicians may be more likely to stress the importance of losing weight, getting enough exercise, quitting smoking, controlling diabetes and other strategies that patients can use to protect their own cardiovascular health.

According to the U.S. National Heart, Lung and Blood Institute, the most current classifications for triglyceride levels are as follows in milligrams per deciliter (mg/dL):

Triglycerides are common types of fats (lipids) essential for good health when present in normal amounts. Like cholesterol, triglycerides are consumed through food and are also manufactured in the liver. They are transported through the bloodstream by the proteins present in various types of lipoproteins.

Cholesterol is mostly transported through the bloodstream by high-density lipoproteins (HDLs, or “good” cholesterol) and low-density lipoproteins (LDLs, or “bad” cholesterol). In contrast, triglycerides are a main component of – and transported by – lipoproteins known as chylomicrons, as well as very low-density lipoproteins (VLDLs, or “very bad” cholesterol). Chylomicrons are only a temporary storage unit for triglycerides. They disappear shortly after appearing in the bloodstream.

Triglycerides are the body’s major form of energy storage. Their presence in the blood is closely related to eating. Triglyceride levels rise dramatically after eating, especially after consuming simple carbohydrates, such as sugar or alcohol. This is because any sugars that are not used immediately as energy are converted to triglycerides and are stored as body fat. The release of stored triglycerides is regulated by hormones, depending on the body’s energy needs. Fasting will stimulate the release of stored triglycerides.

Together with cholesterol, triglycerides form the blood lipids, or blood fat. By measuring the level of fasting triglycerides, physicians can evaluate how much fat is circulating in a patient’s blood. This measure has proven valuable when it comes to diagnosing and predicting cardiovascular disease. High triglyceride levels may contribute to cardiovascular disease by increasing the blood’s stickiness” (viscosity). High triglycerides are considered to be a risk factor for heart disease. They are associated with low HDL levels, high LDL levels and obesity. Because of this association, physicians will often try to lower triglyceride levels in their patients.

Very low triglyceride levels may also be cause for concern. Although low levels are not associated with an increased risk of heart disease, they may be an indication of malnutrition, an overactive thyroid gland (hyperthyroidism) or malabsorption syndrome.

The number of triglycerides in the human body can rise to abnormally high levels when someone eats a diet that is high in carbohydrates (starches and sugars) and/or saturated fats. Triglycerides are usually especially high in people who are obese or who rarely exercise.

High triglyceride levels can also be caused by a number of medical conditions and other factors, such as:

• Diabetes
  
  
• Hypothyroidism, or a lack of thyroid hormone
  
  
• Kidney disease
  
  
• Certain medications, including tamoxifen (used in cancer treatment) and estrogen replacement therapy
  
  
• Familial hyperlipoproteinemias. Rare genetic conditions that involve high levels of cholesterol and/or triglycerides. Some studies have associated genetically elevated levels of triglycerides with an increased risk of heart disease, but others have not.
  
  
• Familial hypertriglyceridemia (also known as type IV hyperlipoproteinemia). Genetic condition in which triglyceride levels are abnormally high. It is often accompanied by insulin resistance, obesity, overactive thyroid and high blood pressure.
  
  
• Familial dysbetalipoproteinemia (also known as familial combined hyperlipoproteinemia). Genetic condition in which levels of triglycerides and cholesterol are abnormally high.
  
  
• Familiar lipoprotein lipase deficiency or Apo-C-II deficiency. Genetic condition in which people lack one of the enzymes necessary to properly break down chylomicrons. As a result, the person may be diagnosed with a high chylomicron level (also known as hyperchylomicronemia or chylomicronemia syndrome or type I hyperlipoproteinemia).
  
  
• Type III hyperlipoproteinemia, a combination of high triglycerides and high levels of very low-density lipoproteins (VLDL).
  
  
• Type V hyperlipoproteinemia, the inability to use and rid the body of triglycerides, leading to high levels of triglycerides in the plasma.

A number of studies have found a link between triglycerides and heart disease. These studies have found:

Other studies have found a clear link between high triglyceride levels and risk factors for heart disease (e.g., low HDL cholesterol, obesity, abnormal glucose metabolism) but no direct link between triglyceride levels and heart disease. Additional research may clarify the role of triglycerides in cardiovascular disease.

Triglyceride levels are measured by a blood test called a complete lipid profile. This chart shows if the results are within the normal range, in milligrams per deciliter (mg/dL):

High triglyceride levels can affect the accuracy of the formula used to calculate LDL levels. Unlike HDL and triglycerides, LDL is not measured directly in most blood tests because it is difficult and expensive to do so. Instead, physicians subtract HDL and one-fifth of triglycerides from the total cholesterol to calculate the LDL.

For example, say a person has a total cholesterol level of 270 and an HDL level, which is measured directly, of 30. The triglyceride level is 250, but this result is divided by 5 to get a score of 50. LDL (270) is calculated by subtracting HDL (30) and triglyceride (50). The LDL level is 190, which is high. This method becomes unreliable when triglyceride levels are above 400. In these cases, LDL must be measured directly.

Research has not demonstrated that lowering triglyceride levels will necessarily lead to improved heart health. However, the strategies recommended for lowering triglyceride levels are all heart–healthy, and many result in an improved cholesterol ratio. These strategies include:

If these strategies are unsuccessful, a physician might prescribe cholesterol-reducing drugs, such as certain fibrates (e.g., fenofibrate) or niacin (nicotinic acid). However, it is important that patients who are prescribed medication to lower triglycerides also make the necessary dietary changes.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about triglycerides:

1. What exactly are triglycerides? How do they differ from the types of cholesterol?
   
   
2. How often should my triglyceride level be tested?
   
   
3. In what range should my triglyceride level be?
   
   
4. What do my test results show?
   
   
5. What are the risks of abnormal triglyceride levels?
   
   
6. Is it possible for triglyceride levels to be too low?
   
   
7. Should I be taking medication to lower my triglyceride level?
   
   
8. How can I change my lifestyle to improve my triglyceride level or maintain a healthy triglyceride level?
   
   
9. Am I currently taking any medications that could affect my triglyceride levels or interfere with testing?