Lipids are fats, such as “good” and “bad” cholesterol or triglycerides, that circulate in the blood as part of normal body metabolism. Abnormal lipid levels may make a person more likely to develop atherosclerosis, a thickening of blood vessel walls that can lead to heart attacks and strokes. People with atherosclerosis sometimes accumulate calcium in their blood vessel walls. A special form of computed tomography (CT) can detect calcium in the blood vessels of the heart (coronary arteries). People with lots of calcium in their coronary arteries are more likely to have heart attacks and strokes. It is well known that abnormal lipid levels in middle age cause calcium to accumulate in coronary arteries and cause heart attacks. However, it is less clear whether abnormal lipid levels at younger ages are harmful, because so few young adults have heart attacks. Showing that abnormal lipid levels in young adulthood contribute to coronary artery calcium would suggest that they are harmful. It would also suggest that younger people need to pay attention to maintaining a healthy lifestyle, even though their short-term risk for a heart attack is low.