What Is 'Bad' Cholesterol?

We often hear about how bad cholesterol is for us — from doctors to nutritionists, the warnings of high cholesterol only grow as we age. But what is cholesterol, and what makes it so bad?

Believe it or not, cholesterol is actually "vital to human life," according to Healthline. It's a waxy substance that's made in the liver and also comes from animal products we eat like meat and dairy. It's carried throughout the body in the blood, and at the right levels, it's a really good thing. It's used as a building block for human tissue, helps produce sex hormones, and helps create bile in the liver. Without cholesterol, these functions wouldn't be possible. But there are two different kinds of cholesterol, and the distinction is important.

This combination of proteins and cholesterol is called a lipoprotein, but when we consume too much cholesterol in our foods, these lipoproteins build up in the blood (via Mayo Clinic). There are both high-density lipoproteins, called HDL, and low-density lipoproteins, called LDL. HDL is "good" cholesterol in that it helps carry excess cholesterol back to the liver, while LDL is "bad" cholesterol that can build up in the artery walls.

When LDL or bad cholesterol levels are high and form deposits in the walls of the arteries, it makes the arteries become more narrow, increasing your risk of heart attack and stroke, due to atherosclerosis, which is a narrowing and hardening of the arteries, according to the American Heart Association (AHA). These risks are increased further when there is also a high level of triglycerides in the body, which are a common type of fat that stores excess energy, per AHA.

High LDL levels are generally caused by unhealthy lifestyles, though they can also be inherited from family members (via AHA). If you eat an unhealthy diet, aren't very physically active, smoke cigarettes, or are overweight, you may be more prone to have high cholesterol. You can manage high cholesterol by limiting the amounts of saturated and trans fats you eat, increasing your intake of fruits, vegetables, poultry, fish, and whole grains, getting more regular exercise, quitting smoking, and losing weight. Adults between ages 20 to 40 that are at low risk of bad cholesterol levels may want to get their levels checked with a simple blood test every four to six years.