Doctor sitting in office with patient talking and smiling © Paul Bradbury, OJO Images, Getty Images

My mother was slender, ate a healthy diet full of fruits and vegetables, and exercised regularly. She died of cancer two months after her 62nd birthday.

My father was a healthy, normal-weight man when a stroke killed him. A friend who never smoked recently died of lung cancer.

So I'm not one of those people who believes living right can somehow immunize us against health care disasters. Disease, accidents and disability can happen to anyone.

Still, a sizable chunk of health care spending in the U.S. wouldn't be necessary if we took better care of ourselves. So-called "modifiable health risk factors," such as how much we weigh, what we eat and drink, how much we exercise and whether we smoke "are responsible for much of the illness, healthcare utilization, and subsequent costs related to chronic disease," as one set of researchers put it. Obesity and smoking alone may add $100 billion to $150 billion a year to U.S. health care costs.

Most of what's written about reducing medical expenses is really more about managing the costs you incur. Finding a good health insurance plan, fighting back when you're denied coverage and negotiating medical bills can help with that.

But this column is about trying to prevent the big costs before they occur.

Here are the 10 costliest medical conditions, according to the U.S. Department of Health and Human Services:

Condition Total cost
Heart conditions $99.2 billion
Trauma-related disorders $80.8 billion
Cancer $80.3 billion
Mental disorders $79.8 billion
Chronic obstructive pulmonary disease (including emphysema and chronic bronchitis) and asthma $64.2 billion
Osteoarthritis and other nontraumatic joint disorders $59 billion
Hypertension $47.5 billion
Diabetes mellitus $40.6 billion
Hyperlipidemia $37.3 billion
Back problems $34.1 billion
Source: Medical Expenditure Panel Survey, 2009  

Many of the chronic conditions listed above have one or more lifestyle components, meaning they can be caused or exacerbated by how we choose to live our lives. Take heart disease. Although genetic inheritance has a role in about half of all heart attacks, lifestyle choices have a far more powerful effect on risk. One study found that the factors that contribute to 90% of heart attack risk are within a person's control. The factors include smoking, alcohol consumption, lack of physical activity, high blood pressure and elevated cholesterol levels (the last two of which can be controlled with medication if lifestyle changes don't work).

Besides, being sick is costly, even with good health insurance. About half of the sickest folks face out-of-pocket expenses that exceed 10% of their family income, according to research conducted for the Public Health Service. Medical bills are a factor in many bankruptcies, even though people typically have insurance at the onset of their illness, accident or disability.

Liz Weston

Liz Weston

Want to spend less on health care? You can improve your odds considerably if you:

Wear a seat belt and stop multitasking in the car.

Injuries are the leading cause of death for people ages 1 to 44, and traffic crashes are the most common cause of serious trauma. So why, with our very lives at stake, do we yak on the phone (increasing the chances of a crash fourfold) or text while driving (increasing the chances of accident by 20 times)?

Put your phone away, so you can keep your eyes peeled for those other idiots who aren't paying attention. An added bonus, on top of reducing your risk of injury or death: You won't face spiraling car insurance premiums after a crash. Off the road, you can reduce your chances of traumatic injury by using appropriate safety equipment, such as a helmet, when you bike or skate; maintaining smoke and carbon monoxide alarms in your home; and removing hazards around the house that could cause falls (the third-leading cause of death from unintentional injury).

Move around.

The American Heart Association recommends you exercise for at least 30 minutes every day. (If you have a dog, you've got a built-in exercise buddy, since your dog needs a 30-minute daily walk to stay healthy, too.) Can't swing 30 minutes? Even 10 minutes a day of moderate aerobic activity, such as a brisk walk, can significantly reduce your risk of heart attack, according to Mayo Clinic researchers. The other benefits of exercise include weight control, lower blood pressure, improved cholesterol, better moods and a reduced risk of diabetes.

Stop smoking.

You don't need me to tell you it's time to put down the coffin nails. Everybody else has been telling you for years. If you want the laundry list of health problems caused by smoking, you'll find it here. The CDC says smoking kills more people every year than motor vehicle accidents, illegal drugs, alcohol abuse, HIV, murders and suicides -- combined. Plus, it makes you stink. Save $5 or more a pack, and your life, by quitting. The website offers links to a variety of resources to help you quit. If you have health insurance, it may even pay for smoking cessation programs.

Lose weight.

Obesity kills, and it often does so in slow and costly ways. Obesity-related conditions include heart disease, hypertension, stroke, type 2 diabetes and certain types of cancer. On average, U.S. health care expenditures in 2006 for people who were obese was $5,148, compared with $3,636 for those who were overweight and $3,315 for people who were of normal weight. Yet two-thirds of U.S. adults are overweight and 35% are obese, defined as having a body mass index of 30 or above. (You can calculate your BMI here.) Many people find programs like Weight Watchers to be effective, although weight loss surgery may be an option, as well. For more, read "What being fat is costing you."

Eat better.

It's not really rocket science. You're supposed to eat more vegetables, fruits and whole grains and less fried, salty and sugary stuff (and watch that soda; even diet pop is associated with weight gain). It's easy (meaning straightforward), but it's hard (meaning difficult to apply), so get educated and consider getting some support. The American Heart Association and the American Stroke Association have some information here.

Watch your back (and your joints).

Losing weight and getting regular exercise can ease many back and joint problems. (Talk with your doctor about what kinds of exercise make sense; those with knee problems, for example, might be better off doing aerobics in a pool than on land.) Something as basic as learning how to lift properly can help you avoid back trouble; bend your knees and hips until you are squatting, keeping your back straight, then lift with your leg muscles.

Get screened.

My mom might be here today if she'd gotten the colonoscopy that doctors now recommend at age 50. (Lower that to age 40 if you have a relative who developed cancer.) Women need mammograms and cervical exams, men need prostate exams. Regular checks of your blood pressure, cholesterol levels, skin (for skin cancer) and teeth are important. Your doctor can help guide you on what you need and when.

Let the screens go dark.

Australian researchers found that increasing your television viewing increases your risk of dying from cardiovascular disease. Even more disturbing, the researchers found that people who spent four or more hours a day in front of a television or a computer had an 80% increased risk of cardiovascular-disease-related death compared with those who watched less than two hours a day. The risk remained even after researchers subtracted the effects of common heart disease risk factors, such as smoking, high blood pressure, high blood cholesterol, bad diet and a big belly. Which means you could be thin, healthy, even a regular exerciser and still face a higher risk of death because of your time staring at a screen. So get up and move. (A bonus from turning off the television is that you don't have to watch all the commercials featuring high-fat and otherwise unhealthy food.)

Use drugs carefully.

Unintentional poisoning is second only to motor vehicle crashes as a cause of unintentional injury death, according to the Centers for Disease Control. Among people 25 to 64, unintentional poisoning actually caused more deaths than motor vehicle crashes. And nine out of 10 unintentional poisoning deaths involve drugs. Prescription painkillers, which includes such drugs as methadone, hydrocodone and oxycodone, were most commonly involved in deadly poisonings, followed by cocaine and heroin. So don't think that you're safe just because you don't use illegal drugs. If you're prescribed a drug, follow the directions. If you can't or can't stop, get help.

Click here to become a fan of MSN Money on Facebook

Don't neglect your mental health.

Exercise can improve your mood, but it's not a bulwark against serious depression, anxiety, phobias or other mental illnesses. And mental illness is far more common than you might think. One in four U.S. adults experiences a diagnosable mental disorder in any given year, according to the CDC, and 46% of Americans will suffer from a mental disorder in their lifetimes. Early intervention and treatment can make a big difference.

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.