Which action improves HDL according to the material?

• A. Prolonged bed rest
• B. Dietary fat restriction
• C. Smoking cessation
• D. Exercise

Answer: (D)

Regular exercise raises HDL by improving the enzymes that handle cholesterol and increasing HDL production, which enhances reverse cholesterol transport — moving cholesterol from arteries back to the liver for excretion. This is the mechanism behind the protective effect of HDL. Aerobic activity like brisk walking, running, cycling, or swimming several times a week reliably boosts HDL levels and function. The other options don’t have as strong or consistent an effect: prolonged bed rest lowers activity and can reduce HDL; restricting dietary fat alone doesn’t reliably raise HDL and may reduce it if healthy fats are cut; quitting smoking does improve HDL but usually to a smaller extent than regular exercise. So, exercise is the action that best improves HDL.