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Epidemiologists love to crunch numbers — and Americans, on the whole, love to ignore them. Even the most health-conscious among us soon grow numb to the storm of statistics warning us about rising levels of obesity or falling levels of exercise or all the other numerical indicators that tell us how unwell we're getting. But on Sept. 14, a team of researchers released a new finding that should cause even the most data-weary folks alarm.

According to a paper published Monday in Circulation, a journal of the American Heart Association, fewer than 8% of all Americans can now be considered at low risk for heart disease. No one needs a statistician's help to know that that means more than 92% of us are not as healthy as we could be, and that's worth paying attention to.

The study was actually the latest in a series of studies, all of which have been part of a program known as the National Health and Nutrition Examination Surveys (NHANES). Administered by the Centers for Disease Control and Prevention (CDC), the program is a four-decade attempt to evaluate the country's health by conducting surveys and physical exams with a rotating sample group of about 10,000 Americans. The first NHANES study was conducted from 1971 to 1975, the second from 1976 to 1980, the next from 1988 to 1994, and the most recent — from which the heart-disease findings are only now being released — from 1999 to 2004.

For that portion of the survey, the investigators focused on people in the 25-to-74 age group and evaluated five different risk factors for cardiovascular disease: blood pressure, cholesterol, smoking history, obesity and diabetes. To be considered at low risk, subjects had to have a blood pressure reading of 120/80 mm Hg or lower without the aid of medication and a cholesterol level below 200 mg/dL, also without drugs. They had to be nonsmokers or at least former smokers, not be overweight or obese, and never have been diagnosed with diabetes. "From a prevention point of view, it's important that Americans achieve as many of these goals as possible," says the CDC's Dr. Earl S. Ford, the lead author of the study.

That's why it's troubling that so few of us did. In the latest NHANES, just 7.5% of adults were considered low risk in all five areas. That's a significant dip from the 10.5% in the 1988-94 survey — which was already a decidedly poor score. Within the adult population, there is no particular demographic slice that's doing particularly well, but some are clearly faring better than others. Among women in the current study, 10.5% were considered low risk (a decrease from 15.5% in the previous survey), compared to just 4.8% of men (down from 5.7%). In the 25-to-44 age group, 12.1% came in at low risk, compared to 3.5% of 45-to-64-year-olds and just 0.8% in the 65-to-74 demographic. Whites, among whom 8.2% were at low risk of heart disease, did better than Mexican Americans (5.3%), and both did better than African Americans (4.6%). The racial gaps have much to do with socioeconomic disparities and unequal access to health care, but there are also genetic factors at play, with certain groups having a higher susceptibility to certain conditions.

Bad as the current numbers are, they are actually not historic lows. In the 1971-75 survey, just 4.4% of the entire sample group was considered low risk; that percentage climbed to 5.7% in the next survey before peaking in the third one. The trend was reversed this time around. "Until the 1990s, we were headed in a positive direction," says Ford. "But then it took a turn."

Surprisingly — and encouragingly — rising heart-disease risk does not necessarily translate to rising heart-disease deaths. Last year, the American Heart Association announced that since 1999, deaths from coronary heart disease fell a remarkable 25.8%. There are a lot of reasons for that happy development, but the leading ones are better drugs and technology, closer adherence to evidence-based practice guidelines and the simple precaution of getting people in cardiac distress to the hospital fast.

All the same, the best way not to need the hospital at all is not to get sick, and even the greatest advances in treatment will amount to little if we can't bring the risk factors under control. The most important factors to attack, the Circulation paper explains, are not cholesterol or tobacco use. Both continue to drop, and with recent federal action to boost cigarette taxes and allow the Food and Drug Administration to regulate tobacco for the first time, the decline in smoking may actually accelerate. (Indeed, last year, the share of Americans who use tobacco fell below 20% for the first time in modern memory.)

The real problems are blood pressure, obesity and diabetes, all of which are relentlessly on the rise. Worse, there's a time bomb in the trend lines. According to a 2008 survey by the CDC, 32% of American children are now overweight or obese, a number that at least appears to have plateaued after a long period of steady increase but one that's shocking all the same. Once those children reach the 25-to-74 demographic, their heart-disease risk could cause the national numbers to explode. "As these children grow up, I expect to see a decrease in the number of people who qualify as low risk," says Dr. Seema Kumar, a pediatric endocrinologist and medical director of the Weight Management Program for Children at the Mayo Clinic in Rochester, Minn. "Our obese children are at high risk of becoming obese adults; some of them are already developing high blood pressure, high cholesterol and diabetes."

The answer to much of this — as is so often the case — is better diet, more exercise and early detection. Such preventive measures form one of the cornerstones of the ongoing health-care debate — one of the few points on which nearly all sides can agree. The authors of the new study call for physicians to be reimbursed for heart-disease-prevention measures like working with their patients to develop weight-loss and smoking-cessation plans and to be allowed enough breathing room in their schedules to let them do good cardiac assessments. Schools and workplaces, the paper argues, should also be in on the prevention game. Since both are places where large numbers of people congregate, they are also places where simple measures like blood-pressure screenings could do the most good.

"Much potential exists to reverse ominous trends in cardiovascular health," the authors write, "but this is unlikely to occur without making prevention of overweight and obesity a national priority." There's no way of knowing when Americans who have heard this refrain again and again will take notice — and take action — but when 92% of us are affected, now seems like a very good time.

• Jeffrey Kluger
• Results of an ongoing government survey suggest that the percentage of American adults considered at low risk for heart disease is dropping