Heart disease is the leading cause of death in the United States, accounting for 1 in 5 deaths, according to the Centers for Disease Control and Prevention (CDC). It encompasses a range of conditions, including blood vessel diseases such as coronary artery disease, problems with heart rhythm, and congenital heart defects, according to the Mayo Clinic. Many heart disease risk factors interact with one another: Stress, for example, increases blood pressure, but so do obesity and smoking, which all increase the strain on the heart.

From high cholesterol to a sedentary lifestyle, here are nine things that increase the risk of heart disease.

1. Smoking

Smoking is a significant risk factor and causes 1 in 4 deaths from cardiovascular disease, according to the CDC. Even people who smoke less than five cigarettes a day may begin to show signs of heart disease, according to the CDC. Non-smokers can also be at risk if they are frequently around people who smoke, with more than 33,000 Americans dying each year from heart disease caused by exposure to secondhand smoke, the CDC said.

Smoking contributes to a condition called atherosclerosis, or the buildup of plaques, fat and other substances within the arterial walls, according to the Mayo Clinic. Chemicals in cigarettes can also contribute to arterial inflammation, which further restricts blood flow, according to the CDC.

2. Overweight or obesity

Those who are overweight or obese are more likely to suffer from heart disease, even in the absence of other risk factors such as diabetes or hypertension. But a 2021 review in the journal Circulation found that obesity also increases the risk of developing type 2 diabetes and hypertension (high blood pressure), which are separate risk factors in their own right. It's not completely clear why having a high body mass index (BMI) may increase heart disease risk, but obesity can cause inflammation within the body, which is known to increase cardiovascular risk.

3. A sedentary lifestyle

A sedentary lifestyle (where a person spends too much time engaging in behaviors that expend little energy) can be a risk factor for the development of heart disease, according to the British Heart Foundation (BHF). Regular physical activity can reduce the risk of developing some heart and circulatory diseases by as much as 35%, according to the BHF, by helping to control blood pressure, exercising the heart and helping to manage blood glucose levels.

4. Diabetes

Both type 1 and type 2 diabetes increase the risk of heart disease. Diabetes leads to high levels of glucose in the blood, and over long time periods, such high blood sugar can damage the nerves that control the heart, as well as blood vessels, according to the CDC. Diabetes also increases the risk of high cholesterol and blood pressure, both of which raise heart disease risk, according to the CDC.

5. High cholesterol

"One of the most common types of heart disease is coronary artery disease," said Dr. Daniel Sado, a consultant cardiologist for London Bridge Hospital, part of HCA Healthcare UK, and lead for the cardiac magnetic resonance imaging (MRI) program at King's College Hospital in the U.K.

"It results in your coronary arteries, which supply the heart muscle with blood, [becoming blocked] with fatty deposits known as atheroma," Sado told Live Science in an email. "This can mean that your heart muscle gets less blood than it needs to function properly."