Learning about modifiable risk factors: Smoking

Hello again. I’m Dr David Leake. Today, I’d like to talk about smoking. The first thing to say about smoking is that it’s the single most preventable risk factor for coronary heart disease. You can’t bring your plasma cholesterol down to zero. You can’t reduce your blood pressure to zero. That’s not a good idea. But you can stop smoking entirely. Smoking reduces your life expectancy on average by 10 years. That’s worth thinking about for a while. If you smoke 25 cigarettes a day, that increases your risk of getting a heart attack by four times. Smoking is also a major risk factor for peripheral arterial disease, a disease of the arteries of the legs.

And even in this day and age, that can lead to the leg amputations. That’s the bad news. The good news is if you stop smoking, your risk of getting a heart attack goes down. Now it’s not only active smoking that’s injurious. If you’re a passive smoker - you are exposed to smoke from people who do smoke - your risk of getting coronary heart disease goes up by about a quarter.

What are the injurious compounds in cigarette smoke? Well, we’re not quite sure, but they could be nicotine, carbon monoxide, free radicals. These are reactive chemicals in smoke. It could be the carcinogenic compounds. Or it could be thiocyanate. And it’s probably a mixture of a number of them. What are the mechanisms by which smoking increases coronary heart disease? Well, there’s a lot of them. Smoking increases blood pressure, which is a major risk factor in itself. It increases the tendency of platelets to aggregate and gives you an increased chance of getting a thrombus. It damages endothelial cells that line blood vessels. It decreases HDL, high-density lipoprotein, and high-density lipoprotein may be a protective factor. Smoking increases inflammation.

And don’t forget that atherosclerosis is an inflammatory disease. Smoking will constrict blood vessels and so if they’re short of oxygen that would make it even worse.

And also, smoke contains carbon monoxide. And that binds with haemoglobin more strongly than oxygen does so it displaces oxygen from haemoglobin. And so if, say, the heart muscle is short of oxygen, that’s going to make things even worse. Also, it decreases the age of menopause in women by 2 to 3 years. Women get coronary heart disease a full decade later than men. After the menopause when they stop producing eggs, that protection goes down. So if you hit the menopause sooner, then the time that which you get protection will also come down.