Smoking and Atherosclerosis

Smoking is one of the most important modifiable risk factors for atherosclerosis. Cigarette smoke contains carbon monoxide, nicotine and many other chemicals, each of which raises the risk in a different way.Carbon monoxide combines with haemoglobin more readily than oxygen does, forming carboxyhaemoglobin. This reduces the oxygen-carrying capacity of the blood, so the heart must beat faster to supply the tissues with enough oxygen. The extra work raises blood pressure.Nicotine stimulates the release of the hormone adrenaline. Adrenaline increases heart rate and causes arterioles to constrict, which also raises blood pressure. Nicotine also makes platelets more sticky, so a blood clot (thrombosis) is more likely to form.Other chemicals in the smoke, including free radicals, directly damage the endothelium lining the arteries. Smoking also lowers the level of antioxidants in the blood, so this damage is repaired less effectively.Damage to the endothelium is the first step in atherosclerosis. It triggers an inflammatory response: white blood cells move into the artery wall and cholesterol builds up, forming an atheroma. The artery narrows, blood pressure rises further and the damage is made worse, a positive feedback loop.Because smoking is a lifestyle choice, stopping smoking lowers a person's risk of coronary heart disease and stroke over the following years.