How long will you live? It's a question that is of more than passing interest to most of us. Usually health journalists put it in a scarier form: What will kill you first? Will it be your over-200 cholesterol? The stubborn extra pounds you're carrying? Your high blood pressure? Will cancer strike you, or will you succumb to some infectious disease, such as pneumonia or tuberculosis?

Maybe some no-see-'ems in your kitchen will undo you, such as the poisonous microbes inhabiting your cutting board. A few months ago, health writers exhorted readers to toss out their wood cutting boards in favor of plastic. Then, only weeks later, they reported a new study that showed wood to be safer after all.

In the face of the overwhelming, and often conflicting, advice regarding so-called risk factors, what does the prudent person do to ensure a long and healthy life?

First, says Thomas J. Moore in "Lifespan: What Really Affects Human Longevity," a thoroughly researched and unusually sensible book, you should beware of medical treatment for such conditions as obesity, high blood pressure and high cholesterol.

According to Moore, the best international studies show that, if anything, medical treatment for these risk factors could actually shorten your life. Studies show, for example, that white women who are treated for high blood pressure die earlier, on average, than white women with high blood pressure who go untreated.

Moore's second bit of advice is to stop worrying and enjoy the life you have. As an individual, you can't do much to prolong your life, apart from breaking self-destructive habits.

The strongest predictor of longevity, Moore says, is the society you live in. Not surprisingly, given their low-fat diets, the Japanese enjoy the longest life spans. But the Swiss, whose diet is among the fattiest in the world, are close behind in second place. The whipped-cream-adoring Austrians are tied for third place with the olive-oil-loving Greeks. Americans, despite having by far the most expensive medical care, are among the shortest-lived people in the developed world.

Noting the dramatic increase in life span in all the developed countries over the last two centuries, Moore writes: "I doubt that a single factor explains the longevity gain. If a single influence exists, it is that stable and prosperous democracies empower individuals and groups to pursue a longer, healthier life in ways too numerous to mention and almost impossible to measure."