Patients stricken with bladder cancer who pose the question of why to Dr. Michael Sarap may well be shocked by the question he might pose in turn: Do you smoke?

They can understand why a smoker would develop lung cancer, but bladder cancer?

"Tobacco smoke gets concentrated and excreted in the urine," Sarap said. "So, smoking is a very big factor for bladder and kidney cancer."

Sarap, a general surgeon who has practiced in Cambridge for 30 years, said the smoking habit also can contribute to heart disease.

"It causes disruption in the lining of the arteries," he said. "It irritates the lining and then plaque, which is calcium and cholesterol together, builds up."

That build-up, atherosclerosis, can restrict blood flow to the heart and lead to a heart attack.

Heart disease, "kidney cancer, bladder cancer, lung cancer — it's amazing, across the world, how much misery comes from just one substance," he said.

Heart disease and cancer lead among the diseases that kill Americans, but the smoking habit is not the only factor that contributes to the development of these and other chronic diseases that have afflicted the modern world.

A host of factors — internal and external — contribute.

The internal factors are genetic. For example, one cited by Sarap is lynch syndrome.

"If you have that, it's almost a 100 percent chance that you're going to get colon cancer," he said.

Another example is the inherited BRCA gene mutation. Any woman who has either of the two variations of that gene is virtually guaranteed that she will contract breast cancer. A mastectomy can reduce the chance, but the woman remains at risk for kidney, uterine or ovarian cancers, Sarap said.

"So, genetics plays a big role," he said. "Cancer is multi-factorial. Some things, we can do something about and some things we can't."

While genes are an internal risk, other risk factors are external — environmental and lifestyle risks. Exposure to chemicals in the workplace or pollutants in the environment can imperil people. Viruses such as the human papilloma virus (HPV) can cause head, neck and cervical cancers.

The factors over which people have the most control are lifestyle factors, Sarap said.

"We're just all overweight — we've got the wrong diet," he said. "Many of us use alcohol and tobacco to excess and that causes issues.

"Stress is a big factor for heart attacks. That can be physical stress, but also emotional stress. Any kind of stress causes the pituitary and adrenal glands to push out epinephrine and norepinephrine. That increases your blood pressure. It constricts your blood vessels so there is less blood flowing to certain organs."

Genetics figures prominently in disease risk, but altering one's lifestyle in a positive way can make a substantial difference in lowering one's risks, he said.

"If you smoke, stop. Get into a fitness routine, or, at least, walk every day. Look at your diet."

When questioned about claims that the so-called "Standard American Diet" contributes to the development of cancer, heart disease and other chronic ailments, Sarap agreed there is some validity to the criticism.

What is wrong with our diet?

"It's high fat, low fiber and too much red meat," he said.

He cited an example from Africa.

"Colon cancer is an incredibly rare disease in [parts of] Africa where people have a grain based diet," he said. "Diverticulitis is unheard of in Africa … until the people move to the big city and start to get meat or a Western kind of diet."

It is difficult to criticize those who tout a plant-based diet, he suggested.

"You don't need meat," he said. "You can get protein from other things. Vegetarians live their whole lives without eating meat and they're as healthy as can be."

Sarap agreed there are too many factors for people to walk around thinking about every day, but they can concentrate on the major ones.

So, in summary, what can people do in general to improve their chances of remaining healthy well into their old age?

"Try to avoid toxins when you can," he said. "Cigarettes is number one on the list and secondary smoke is right there with them.

"The problem is where we live in rural America. Probably the number one reason why our cancer rates and our cancer death rates are higher than anywhere else in the country is smoking. We still have a huge number of people who smoke despite every warning we give them.

"People need to maintain a good weight. You don't have to go to the gym and sweat, but you have to have some activity. So a daily walk is really a big thing. Try to limit how much red meat you eat and increase your fruit, vegetables and fiber."

(EDITOR'S NOTE — See the community section of The Sunday Jeffersonian for stories about local people who have taken action against one of the risk factors.)