Cholesterol is a type of body fat, or lipid. A serum cholesterol level is a measurement of certain elements in the blood, including the amount of high- and low-density lipoprotein cholesterol (HDL and LDL) in a person’s blood.

Serum cholesterol levels also show the amount of triglycerides present. Triglycerides are another lipid that can be measured in the blood.

According to the American Heart Association, low-density lipoprotein (LDL) cholesterol is often considered bad, while high-density lipoprotein (HDL) cholesterol is considered good.

A person’s serum cholesterol level can indicate their risk for conditions such as heart disease.

In this article, we explore what serum cholesterol shows, what healthy ranges are, and how to improve levels with changes to lifestyle and diet.

What is serum cholesterol?

serum cholesterol represented by heart next to stethoscope.
Serum cholesterol levels can help to determine a person’s risk of heart disease.

Cholesterol is a waxy, fatty substance. Some cells in the liver produce it and release it into the bloodstream.

LDL cholesterol can build up in a person’s arteries, clogging them and reducing blood flow. This is why cholesterol is often linked to heart disease.

With a blood test, a doctor can measure levels of:

  • HDL cholesterol, which is good
  • LDL cholesterol, which is bad
  • triglycerides, which are a type of fat bundled with cholesterol

Total serum cholesterol is calculated by adding the HDL level, the LDL level, and 20 percent of the triglyceride level present in a blood sample.

Cholesterol plays a vital in many of the body’s processes, including:

  • building cellular membranes
  • making hormones
  • metabolizing vitamin D in the skin
  • producing bile acids to digest fatty foods

While LDL cholesterol tends to build up and block arteries, HDL cholesterol helps to mop up other cholesterol in the blood and unstick it from artery walls. This is why HDL cholesterol is considered good.

Normal ranges

Doctors once determined whether a person’s serum cholesterol level was healthy by comparing it to established normal ranges.

Previously used guidelines, reported in milligrams per deciliter (mg/dL) of blood, include:

Age and sex Total serum cholesterol HDL level LDL level Triglycerides
All aged 19 and younger At most 170 mg/dL At least 45 mg/dL Less than 100 mg/dL Less than 150 mg/dL
Females aged 20 and older 125–200 mg/dL At least 50 mg/dL Less than 100 mg/dL Less than 150 mg/dL
Males aged 20 and older 125–200 mg/dL At least 40 mg/dL Less than 100 mg/dL Less than 150 mg/dL

Doctors now take a wider range of factors into account before deciding if someone’s cholesterol levels are unhealthy or require treatment.

Some risk factors a doctor may consider when evaluating a serum cholesterol level include:

  • the ratio of HDL to LDL cholesterol
  • triglyceride levels
  • obesity
  • high blood pressure
  • whether the person is a male aged 45 years or older
  • whether the person has experienced menopause
  • smoking or tobacco use
  • family history
  • type 2 diabetes
  • lack of physical activity or a sedentary lifestyle
  • a diet high in saturated and trans fats
  • excessive alcohol consumption
  • a diet very high in carbohydrates, especially when refined
  • metabolic syndromes
  • chronic inflammatory conditions

Health impacts of serum cholesterol levels

Overall, a person with higher levels of HDL cholesterol and lower levels of LDL cholesterol will have a healthier serum cholesterol measurement.

This is because HDL cholesterol helps to reduce the presence of LDL cholesterol in the blood. It can also prevent LDL cholesterol from collecting and forming hard deposits called plaques, which stick to artery walls and reduce blood flow.

Plaques can become so large that they cause the arteries to narrow and stiffen, which can contribute to heart disease.

A significant amount of LDL cholesterol in arteries can prevent enough blood and oxygen from reaching organs and tissues, causing severe health complications.

A chunk of a plaque, known as a thrombus or blood clot, can also break off and become stuck in a narrower or restricted artery. This will make the blockage of blood more severe.

Complications associated with high serum cholesterol levels include:

Less is known about how triglycerides impact health. However, people with high levels of triglycerides tend to be at risk for similar conditions, including diabetes, high blood pressure, and heart disease.

Below is a 3-D model of high cholesterol, which is fully interactive.

Explore the model, using your mouse pad or touchscreen, to understand more about the impact of high cholesterol levels.

Reducing LDL cholesterol levels

The liver produces enough cholesterol to meet all of the body’s needs. Any cholesterol consumed in foods and drinks, known as dietary cholesterol, is excess. This extra, unnecessary cholesterol is more likely to build up in the bloodstream.

Changing the diet is the most effective way to reduce levels of unhealthy cholesterol and increase levels of healthy cholesterol.

Saturated and trans fats should account for no more than between 5 and 6 percent of a person’s daily intake of calories.

If a person consumes 2,000 calories per day, they should only take in between 11 and 13 grams of saturated fat each day.

A person can also achieve and maintain healthy cholesterol levels by making changes to their lifestyle.

The following tips can help a person to reduce their levels of LDL cholesterol:

  • eating fewer full-fat dairy products, such as whole milk, butter, cream, and cheeses
  • eat fewer red meats, pork, lamb, and poultry with skin
  • avoiding packaged, fast, and fried foods
  • limiting the consumption of oils high in trans fats
  • avoiding some tropical oils and butters, especially those derived from cocoa, coconuts, palm, and palm kernel
  • eat fewer refined carbohydrates, such as those found in pastries, breads, crackers, and chips
  • avoiding sugary foods and drinks, such as candies, chocolate bars, juices, prepared smoothies, sodas, and energy drinks
  • losing weight or maintaining a healthy weight
  • quitting smoking and avoiding secondhand smoke
  • reducing or avoiding alcohol consumption
  • exercising regularly
  • reducing or managing stress
  • treating related medical conditions, including diabetes and high blood pressure
  • having planned meals
  • snacking on fruits and vegetables, rather than unhealthful prepared foods

Keeping a food diary can help a person to identify room for improvement and develop more healthful habits.

Increasing HDL cholesterol levels

healthy vegan meal with plant food
Increasing the proportion of whole grains and vegetables in a person’s diet can help maintain healthy cholesterol levels.

The following activities can boost a person’s levels of HDL cholesterol:

  • using oils with fewer trans fats, such as those derived from olives, sunflowers, canola, and corn
  • eating more whole fruits and vegetables
  • eating more whole grains and cereals
  • replacing meat with plant-based protein sources, such as walnuts, almonds, beans, tofu, seeds, quinoa, and whole grains
  • eating skin-free poultry and fish such as salmon, trout, herring, and mackerel
  • increasing the intake of dietary fiber, either by eating more leafy greens and whole grains or by taking supplements
  • drinking low-fat milk or replacing milk with a dairy-free alternative
  • getting regular exercise

A doctor may prescribe medications, often statins, for people with high cholesterol that does not respond to dietary and lifestyle changes.

Outlook

Cholesterol may have a bad reputation, but it is crucial to many bodily processes. However, the liver produces all the cholesterol a person needs.

Serum cholesterol can give an overview of a person’s cholesterol levels. The amount of triglycerides and LDL and HDL cholesterol in the blood can indicate the risk of a severe heart condition, such as a heart attack or stroke.

The American Heart Association recommend that adults older than 20 have their serum cholesterol levels and other indicators of heart disease checked every 4 to 6 years.

A person with a higher risk of complication related to high blood pressure may need to have their serum cholesterol levels checked more frequently.