Here's why "the number" is so misleading. Total cholesterol is calculated by adding LDL (bad cholesterol), HDL (good cholesterol), and one-fifth of your triglyceride total. "We have been using this formula of adding a bad thing to a good thing and factoring in one-fifth of a bad thing, and it's not useful," Dr. Mays says.
That's one reason 50% of people who have a heart attack have normal cholesterol readings.
Effects of diet and exercise
A smarter way of looking at cholesterol risk is by component. LDL, or bad cholesterol, is very responsive to good nutrition and exercise. The target number is less than 100 mg/dL. It's not uncommon for LDL to swing up by 40% in response to a sedentary lifestyle and a diet high in saturated and other unhealthy fats, according to Dr. Mays.
It can also drop by up to 40% in response to a heart-healthy diet and regular exercise.
One in 500 people has an inherited risk of extremely high LDL and should be put on statins to control their risk of heart disease.