Because LDL drops when you have cancer, or a heart attack. That is, the U shape is a result of reverse causation. When you look at longitudinal data there’s no

Because LDL drops when you have cancer, or a heart attack. That is, the U shape is a result of reverse causation. When you look at longitudinal data there’s no U shape - it’s straight as an arrow. Higher LDL-c -> more heart disease.