Science / Medicine : Doctors can’t guarantee that doing certain things--or avoiding them--will protect your health. But knowing the risks puts you in control. Take this test to learn: : Are You Risking Your Health? : Answer These Six Questions

1. You are about to plan a 1,000-mile journey, and you aren’t pressed for time. Rank the following means of transportation from the safest to the riskiest: bus, train, plane and passenger car.

2. What would you say kills more Americans annually: heart disease, cancer, or automobile accidents?

3. You’re a healthy 45-year-old man, slightly overweight. Your father and his brother both died in their 50s of heart disease. Your mother, now 65, has had Type II diabetes for several years. Are you likely to get one of these ailments?

4. Winston Churchill, not to mention your Aunt Harriet, drank brandy and smoked habitually and was overweight besides. Both lived into their 80s and died peacefully in their sleep. Does that prove there is something health experts don’t know?

5. You’re a 43-year-old woman, a good cook, and you like a glass of wine or two with fine food. You were upset to read recently that even moderate alcohol consumption may double a woman’s risk of getting breast cancer. The experts further stated that quitting now might not reduce the risk. However, you stopped drinking wine. Your sister is a teetotaler. Are you twice as likely to get breast cancer as she is?

6. You’re 50, female, and a smoker. Your last checkup showed that both your blood pressure and blood cholesterol level were somewhat higher than they should be. You know this means that you risk a heart attack or stroke, but you read an article that said that even 50-year-old male smokers with high blood pressure and elevated cholesterol have only a 13% chance of getting sick within six years.

So you are looking on the bright side: you have an 87% chance of staying healthy for the next six years. Is this a constructive attitude?

Efforts to identify health risks--and reduce them, if possible--are as old as medicine itself. Hippocrates advised his fellow physicians to “consider the seasons of the year and what effects each of them produces” and to take note of what people drank and ate and how they lived.

Scientists today are still looking for the determinants of health, albeit with a little more sophistication and scientific knowledge. Epidemiology (literally, the study of epidemics) is the attempt to identify the factors that cause diseases and injuries to determine what the probabilities are that they will cause them, and to determine how to decrease or eliminate the identified risk. This is often referred to as risk hazard appraisal, which is of growing importance in medical science, especially in the effort to prevent disease and promote health. Once the risk factors are known, the next job is to make changes in the environment (for example, to persuade manufacturers to install seat belts of a certain design) and to persuade people to change their behavior (for example, get them to fasten the belt).

In the science of risk assessment, there is no such thing as absolute safety, but you can choose to widen or narrow your safety margins. And though scientists may assess the risks, how you manage your life is up to you.

The purpose of the questions above is not so much to produce correct answers as to invite you to figure your odds.

Questions 1 and 2: Figuring the odds.

Of these questions, only the first two have fairly straightforward answers. You’re safest in a bus and in greatest danger in an automobile. (More than 10 people die per billion automobile and taxi miles; but it takes more than 2 billion bus miles to produce a fatality. Trains and planes are 10 times safer than cars, but only about half as safe as buses.) But whether they travel or stay at home, more Americans die of heart disease each year than of anything else.

Questions 3 and 4: Heredity is not destiny.

If your father died young of a heart attack, you have a good chance of following in his footsteps. Knowing your inherited liabilities, though, gives you an excellent opportunity to alter them. The genetic odds may be lowered significantly if you are not overweight, keep your blood pressure under control, and maintain a low blood cholesterol level. If your mother has diabetes, that’s an indication that weight control and exercise are crucially important for you.

For many of us, familial tendencies constitute an emotional trap. People whose parents or grandparents died at comparatively young ages of heart disease or cancer, or some other disease with a genetic component, usually realize that this heritage works against them and may falsely conclude that taking care of their own health is irrelevant. On the other hand, if all your relatives were as indestructible as Winston Churchill or the hypothetical Aunt Harriet, you may have an equally false sense of invulnerability.

Researchers may one day unravel the genetic code and come closer to accurately predicting your chances of getting a disorder such as heart disease or hypertension. But today only a few diseases are known to have purely genetic causes, for example, hemophilia, in which a blood-clotting factor is absent; sickle-cell anemia, a blood disorder that occurs most commonly among people of African descent; cystic fibrosis; and certain forms of kidney disease.

In many ailments that show signs of running in families, such as cancer, heart disease, or diabetes, heredity is only one factor in the mix. Your biological and cultural heritage and your environment interact, and it’s the interaction that counts. Your diet or exercise habits or your environment may foster, or foil, the tendencies you were born with.

Question 5: Alcohol and breast cancer

Last year, as reported in the New England Journal of Medicine and subsequently in scores of newspapers and magazines, studies by two prestigious research groups independently demonstrated a link between alcohol intake and breast cancer. A woman who drank even as few as three beers or glasses of wine weekly was found to have a 50% greater lifetime risk of developing breast cancer than a nondrinking woman. Widely publicized along with that figure was another statistic: that one American woman out of 11 develops breast cancer at some time in her life. That’s a risk of 9%. It seems logical to conclude therefore, as many reporters did, that women drinkers run a risk closer to 14%, a terrifying narrowing of the safety margin.

But here’s what very few of the reports made clear: The 1-in-11 figure applies to all American women indiscriminately, from age 1 to 85. That is, it’s a lifetime average and does not describe the odds for an individual over shorter intervals. The incidence of breast cancer in the population rises with age. A 40-year-old woman has about a 3.3% chance of developing breast cancer by age 60. If she’s a moderate drinker her chances would increase by half--to about 4.8%--if the reported studies are correct. That’s a little less horrifying than 14%.

Furthermore, though the two studies considered other risk factors, they point up many problems. For example, the estimation of what the women actually ate and drank was based on poor data obtained only at the beginning of the studies, which lasted from four to 10 years. The investigators did not determine the women’s previous eating and drinking habits or whether these habits changed while the studies were going on. In addition, they did not rule out the chance that something besides alcohol is increasing the cancer risk in the lives of moderate drinkers.

Then in March, Dr. Susan Chu of the Centers for Disease Control in Atlanta reported that a new study of 7,000 women (based on a different approach) found no association at all between alcohol and breast cancer. Clearly, a lot more medical research needs to be done. If you’re a woman wondering whether an occasional drink will do you good or harm, the answer is still up in the air; no cause-and-effect relationship between alcohol and breast cancer has yet been demonstrated. Heavy drinking is of course associated with many disorders. But women who drink occasionally need not berate themselves for having unwittingly shortened their lives.

Question 6: Heart attack roulette.

A 50-year-old smoker, male or female, with elevated blood cholesterol and blood pressure is seriously courting cardiovascular disease. You may have only a 13% chance of developing it, since neither you nor your doctor has any way of predicting whether you’ll fall into the lucky 87% who do not develop heart disease or the unlucky 13% who do. If these sound like favorable odds, you may decide not to make any changes in your habits. However, a more realistic way to consider the odds is as follows. If your risk factors were low (that is, you didn’t smoke and your blood pressure and blood cholesterol levels were low), your chances of having a heart attack between age 40 and 64 would be only 6%. However, if you continue to smoke and do nothing about your other risk factors, your chance of having a heart attack during these years is 40%. This is a very big difference. Giving up cigarettes, controlling your blood pressure, and lowering your blood cholesterol level would significantly widen your safety margin. Obviously, that’s the constructive action to take.

Another example of this kind of reasoning can be seen in the relationship between oral contraceptives and heart attacks. High-dose oral contraceptives increase the risk of heart attack by a factor of 4. This sounds like a very large increase. However, if you’re a 20- to 24-year-old woman, your heart attack risk is less than 1 in 500,000. Thus a fivefold increase represents only about 5 in 500,000 (or 1 in 100,000). This means that if all 8.5 million American women in this age group were to take oral contraceptives, 80 of them (instead of the expected 17) would have heart attacks. This would produce many fewer deaths than might result from unwanted pregnancies in the same age group. And even this small risk has been markedly reduced by the new low-dose estrogen contraceptives.