Q: Is it possible to prevent, or at least reduce, your risk of cancer?

A: Absolutely, it is. It is possible both to reduce the risk that your cells will turn cancerous, and to catch cancer early and prevent it from causing suffering. But first let’s define some terms.

What does it mean to say that a “cell turns cancerous”?

Cancer is uncontrolled cell growth. Most cells “grow” not by becoming larger, but from dividing. (An exception: Fat cells grow not only by dividing, but also by becoming larger.) One cell becomes two, two become four, four become eight, and so on.

Most cells should periodically divide, but in a controlled fashion. For example, as old cells die, they need to be replaced. But that process of replacing old cells is carefully controlled.

When a cell turns cancerous, growth is not controlled. In most cancers, the uncontrolled growth first causes a mass of cells — a tumor. (With cancers of blood cells, there is no tumor mass because blood cells don’t stick together.) The cells in the tumor then can spread, typically through the blood, to other parts of the body.

You can reduce the risk of cells turning cancerous with lifestyle changes.

Stop smoking:

Exposure to tobacco smoke (including secondhand smoke) — from cigarettes, cigars and other tobacco products — increases the risk of lung cancer. Smoking also boosts your chances of developing cancer of the mouth, throat, esophagus and colon. If you smoke, ask your doctor about quit-smoking programs.

Maintain a healthy weight:

Overweight and obesity increase the risk for many types of cancer. These include breast cancer (in postmenopausal women) and cancers of the colon, rectum, endometrium, esophagus, pancreas and kidneys. A healthy diet and regular exercise can help you maintain a healthy weight.

Eat a healthy diet:

People who eat diets rich in fruits and vegetables (particularly broccoli, kale, cabbage, cauliflower and tomatoes) have lower rates of cancer. So do people who eat relatively little meat (particularly processed and cured meats, such as bacon, sausage and cold cuts).

That said, don’t focus on any single food or group of foods. It’s an overall healthy diet that counts.

Exercise regularly:

Exercise is yet another way to reduce your cancer risk. Aim for at least 30 minutes of moderate-intensity exercise, most days of the week.

Protect yourself from the sun:

Skin cancer is one of the most common cancers. To reduce your risk, stay out of the sun when it is strongest (from 10 a.m. to 4 p.m.). Apply plenty of sunscreen with an SPF of at least 15, and reapply it every two hours. Wear sunglasses and wide-brimmed hats.

Get screened:

Screening tests can’t prevent cancer. But they can catch cancer early, before symptoms appear, and when chances of survival are at their best. (On my website, AskDoctorK.com, I’ve put a list of cancer screening tests, along with when and how often to get them.) Discuss screening tests with your doctor. He or she can help you tailor the recommendations based on your individual risks and preferences.

• Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.