Since an iron lung costs quite a few dollars, the prevention of polio cannot make sense. Right? If that one has you scratching your head, with a “say what?” dangling from your lip, we are on the same page. Let’s populate it accordingly. Of course prevention can save dollars. But that will only be the case when what we refer to as “prevention” really makes sense.

Prevention enthusiasts, and I certainly do count myself among them, have long contended that preventive medicine has the potential to add years to life, add life to years, and save a lot of money into the bargain. Members of the other side, let’s call them the dubious, because no one is really a prevention “detractor,” have argued that the former points may be true, but the last is not.

Prevention, especially in the form of clinical preventive services such as cancer screening, costs money. And since part of the preventive medicine imperative is to find and fix disease early, prevention encourages healthy people to undergo medical testing to identify problems no one knew they had. Suddenly there is expense where there would have been none.

This case, and variations on it, has been made many times, including very recently in Reuters. The Reuters article, which some of my colleagues have already confronted, cites a recent report by the Trust for America’s Health on transitioning the U.S. system from “sick care” to genuine “health” care, and a paper published in 2010 in the peer-reviewed journal Health Affairs. The analysis in Health Affairs suggests that widespread use of preventive services could help us all save 0.2% of personal health spending in the U.S.

The folks at Trust for America’s Health, clearly prevention proponents, seem a bit more sanguine about the potential savings involved. The reporter at Reuters, however, apparently something of a nihilist, throws the “annual physical” into the prevention mix, noting that collectively these exams cost a lot of money and do little if any good.

However, as a board-certified specialist in preventive medicine, and co-author now of four editions of a textbook on the topic, I must protest! There is no formal recommendation for annual physicals by our college, and we know they are not cost-effective. Everybody knows. They are simply a holdover from the long traditions of medicine, and a more formal embrace of evidence-based preventive medicine would consign them to history. Many of us have already done so.

But even if we define clinical preventive services more reasonably, we are left with uncertainty and debate about whether prevention saves money. This debate is ostensibly all about dollars, but should be more about sense, namely, the sense we make or forsake when throwing the term “prevention” around. That which we call prevention is not all equally sweet, or cost-effective, let alone cost-beneficial.

Of course prevention as commonly defined doesn’t save money. Cancer screening is about saving lives, not money. Trauma surgery doesn’t save money, either, for whatever that’s worth.

Since prevention is about, well, preventing bad things, then all of medicine might be considered variation on the preventive medicine theme. A construct called Leavell’s Levels essentially defines preventive medicine in just such terms, ranging from the promotion of health (primary prevention) to the prevention of dysfunction even after serious chronic disease is established (tertiary prevention).

Risk factors are treated to prevent diseases. Diseases are treated to prevent permanent illness or disability or complications. Calamities are treated to prevent death.

All of this costs money. In contrast, we could do nothing for free. We can die, and let others do so, for free. It would save a lot of money to prevent nothing. Just let come what may.

I trust we all agree there’s a problem with this. For one thing, we value life more than money (I hope!). For another, there is, in fact, a financial impact when we check out. We are no longer here to do any work, or provide for our families. We leave a hole in the economy.

There is, in particular, a gaping economic hole if we check out slowly rather than fast. If we are sick for a long while before dying, and that, by definition, is what “chronic disease” is all about, and chronic disease is overwhelmingly the primary exit route for those of us in modern society, then we work less, or not at all, long before dying. We become less productive, costing the same or more, contributing ever less. Among my friends and colleagues are world-class health economists, and even they have difficulty getting their heads around all of these so-called “externalities,” and the extent to which they alter the pecuniary assessment of prevention.

But, of course, treating chronic illness is a very imperfect solution to this problem. The issues of illness and impaired function invariably persist, if to a lesser degree, with treatment. The costs of disability attached to chronic diseases are then compounded by the costs of chronic treatment. And, in fact, the better we get at preventing death despite chronic disease, cancer, cardiovascular disease, diabetes and its complications, dementia, respiratory diseases, stroke, and so on, the longer that period of poor health and high cost.

There are lesser and greater problems, however, with this constrained and unflattering view of prevention.

The lesser problem is the often-overlooked financial benefit of so-called “health care” to the economy at large. We make a big fuss about how much disease care costs our economy. But it also contributes, and mightily. Throughout the great recession, one of the few sectors of the economy that never really slowed down, and that consistently offered jobs to those qualified was, yes, indeed, health care. Biomedical research is big business. It costs money but it also creates jobs and, from time to time, breakthroughs.

Pharmaceutical companies, health care companies, and pharmacies populate the Fortune 100, and the Dow Jones Industrial Average. They are engines of the economy. Hospitals, clinics, medical practices, and device companies all make their contributions as well. Consider what would happen to the economy if all of these jobs went away.

Frankly, it’s well above my pay grade to figure out whether our disease care system is more good than bad, or vice versa, for the economy overall. A lot of money goes into it, yes. But that is money in circulation, being spent, and spent again. Like all money changing hands, it means jobs, purchases, and tax revenue. These are the building blocks of economic vitality. If all of this is bad because of the money changing hands, then wouldn’t it be better to “save” all the money we spend on housing as well, and live in caves? Wouldn’t it be better to save all the money we spend on education?

So, the reality is this: Yes, we spend way too much on disease care. But probably not because of the financial costs, per se. But rather, because those financial costs represent human costs: years lost from life, life lost from years. Jobs not done. Families undone.

Which, of course, reframes the whole concept of prevention and costs. It’s not about saving money. It’s about saving lives. And once that’s clear, then it becomes relevant to ask: What’s the best we can do for lives? And what is the most cost-effective way to do it?

That, largely, has been the defense of prevention, and it is a good one. But as noted several paragraphs above, this is all about the lesser problem. The greater problem has to do with what we mean by “prevention” in the first place.

The iron lung, with which this jeremiad began, is a costly half-measure. It’s a form of prevention, yes; it prevents death in the early stages of poliomyelitis. But it’s not nearly as good as preventing polio outright, which of course is now the global norm, courtesy of immunization. Once polio is eradicated, assuming we can get there, its prevention becomes permanent and free. Were we to look at the iron lung and renounce further prevention efforts as financial folly, no such progress could occur.

Similarly, dialysis is expensive; preventing end-stage kidney disease brought on by hypertension or diabetes, or, better still, preventing hypertension and diabetes in the first place, is dramatically less so. Coronary bypass surgery is expensive; preventing coronary disease in the first place can be dramatically less so. Bariatric surgery and potential alternatives cost money, while avoiding that weight gain in the first place could be free.

And, similarly, screening for cancer in a population that gets it often enough to warrant screening is a fairly expensive half-measure. Better than nothing, certainly; but not nearly as good as going all the way. What would going all the way look like? Preventing so much cancer outright that screening for it is no longer warranted.

Is that possible? Almost certainly, yes. Studies (1, 2, 3, 4, and so on) spanning decades consistently indicate that fully 80 percent or more of all chronic disease, including cancer, can be eliminated outright with knowledge already at our disposal. Not treated more effectively. Not managed. Eliminated.

The method? Good use of feet, forks, and fingers. Being active, eating well, and not smoking. Lifestyle as medicine. That’s it.

We can avoid tobacco for free. We can be active for free, although we can also spend money on it if so inclined. And we have to eat one way or another. We can eat better without spending more money than we already do.

If we got down to the bedrock of true prevention, lifestyle as preventive medicine, we could add years to life, add life to years, and save a whole lot of money by putting to use the science and sense long at our disposal. Doing so will, of course, require changes in how we think about health, changes in our culture. But culture is what we make it, and we can change it for free.

Which brings us to the bottom line, figuratively and literally. We have the science we need to eliminate outright most of what ails us. Prevention could save us a whole lot of dollars if, when we used the term, we made a bit more sense.

David L. Katz is the founding director of Yale University’s Prevention Research Center.