If you've ever wondered whether dragging yourself to the gym or denying yourself dessert is really worth the effort, here's heartening news: Research raises the tantalizing possibility that many healthy behaviors provide a double benefit, by reducing the risk of deadly disease and slowing the rate of aging.

The clues come from many quarters, including studies on the impact of lifestyle, and animal research aimed at extending life span. Late last year, for example, scientists announced that concentrated resveratrol, a substance in red wine and grape juice, helps mice live longer by reducing disease and apparently inhibiting aging. Resveratrol pills seem to cause many of the same protective changes as severe caloric restriction, the only method known to enable animals to live beyond their usual maximum life span.

No one knows whether concentrated resveratrol would be effective and safe in humans. But the findings dovetail with other research that suggests aging and disease may share many of the same possible causes, notably DNA damage, oxidation, inflammation, and increased resistance to the hormone insulin. In theory, exercise and other lifestyle steps shown to counteract those factors may help keep people healthy and vigorous to a ripe old age.

Aging and illness are intertwined in another crucial way, which lets you take charge of your health rather than just accepting physical deterioration as the inevitable result of aging: Studies suggest that the frailty of many older people actually stems from undetected cardiovascular disease (see "The hidden cause of frailty"). So spotting and treating the disease may substantially slow the physical decline.

Here's a rundown of the latest research about longevity, including the possible new reasons to practice the healthy habits that may help you live a long and active life.

How and why people grow old involve complex physiologic changes that scientists don't yet fully understand. But some key components are starting to emerge.

One is heredity, which typically determines about 30 percent of your life span, says Thomas Perls, M.D., M.P.H., director of Boston University's New England Centenarian Study. (Your genes generally contribute more than that if your parents lived past about age 90 or died prematurely from disease, Perls says.) Findings from the study and other research have led to the identification of several likely "longevity-enabling" genes, including a few that influence the risk of heart attack, stroke, and dementia.

Lifestyle and environmental factors determine much of the remaining 70 percent, scientists say. The most dramatic example is severe caloric restriction, which in animals stimulates increased repair of the DNA damage that may contribute significantly to aging.

Whether a nutritious, very low-calorie diet can lengthen human life is not known. But people who have voluntarily eaten that way for years, consuming 30 to 44 percent fewer calories than the typical American, show less age-related decline in heart function and less narrowing of the arteries, according to one small study. And preliminary findings from the first controlled clinical trial in humans show reduced DNA damage and improvements in two proposed markers of longevity: lower body temperature and insulin levels. Several drug companies are currently testing "caloric-restriction mimetics," or substances that cause the same beneficial changes as a restricted diet does.

But you don't have to wait for those pills. A study of more than 5,000 middle-aged men in Hawaii has identified for the first time a set of factors that appear to predict "exceptional survival." That means living to age 85 free of major disease and with physical and cognitive function intact. The 655 healthy survivors had no signs of insulin resistance. They had good grip strength, suggesting physical reserves that could counteract age-related loss of muscle. And they had little fat, which tends to produce inflammatory molecules and to reduce both insulin sensitivity and levels of human growth and other vital hormones. Keeping blood pressure down and limiting smoking and alcohol intake also paved the way to a healthy old age.

The following sections describe the key steps that can help you develop many presumably life-prolonging features.

Exercise "is the closest thing we have to a fountain of youth," says S. Jay Olshansky, Ph.D., a longevity researcher at the University of Illinois in Chicago. Working out can reduce blood pressure and inflammation, boost responsiveness to insulin, improve cholesterol levels, and cut the risk of life-threatening disease.

In general, studies lasting many years have shown that being active cuts the risk of premature death by about 50 percent. And exercise can counteract the muscle loss and certain other debilitating effects of age. For example, a recent study showed that aerobic exercise increased brain volume in older adults, probably in part by stimulating growth of new brain cells. And it's never too late to start: In a study of sedentary women ages 65 and up, those who increased their physical activity to the equivalent of walking just a mile a day were half as likely to die over the following six years.

Even everyday activity--washing dishes, climbing stairs, working in the garden--may prolong life, too. In one study of people ages 70 to 82, those who were active for an extra 75 minutes a day were 30 percent less likely to die during the six-year period, after the results were adjusted to account for pre-existing illness.

The Web site of the American Heart Association's Start! Program lets you estimate your intake and expenditure of calories, find ways to add more activity to your daily routine, and track your progress. For more conventional exercise, older adults can find special programs at many senior centers and health clubs.

Excess fat, especially around the belly, produces an array of potentially harmful biochemical changes. For example, one study found that a man of average height who gained 30 pounds experienced a drop in testosterone normally linked with 10 years of aging. Moreover, the metabolic syndrome, defined partly by excess abdominal fat, is a potent risk factor for diabetes and heart disease, both of which can accelerate aging.

Even modest weight gain may increase mortality. For example, the Nurses' Health Study, which followed 116,000 women for 24 years, linked gains of just 9 to 22 pounds with a 15 percent higher death risk; regular exercise reduced but did not eliminate that threat.

In the recent clinical trial of caloric restriction, moderately overweight people who cut calories by 25 percent lost about a tenth of their body weight in six months and improved several likely markers for longevity. More important, a second group achieved comparable results by cutting just half that many calories and making up the difference with energy-burning exercise.

Increasingly, researchers are finding that foods known to protect against disease act in ways that may also affect aging.

The studies suggest it's wise to:

• Pick nutrient-dense, low-calorie foods. While severe caloric restriction is usually impractical, some researchers believe that "calorically selecting" foods--emphasizing low-calorie, high nutrient produce, for example--may yield similar benefits. People in Okinawa, Japan, generally eat that way and live longer than probably any other group.
  
  
• Eat like a Greek. Research has linked the Mediterranean diet--lots of fruits, vegetables, whole grains, nuts, legumes, fish, and monounsaturated fats such as olive oil, plus moderate amounts of wine--with longer life and less heart disease. In a two-year clinical trial, that diet reduced inflammation and insulin resistance significantly better than a "heart healthy" low-fat diet. It also eliminated the metabolic syndrome--excess belly fat, hypertension, high blood sugar and triglycerides, and low levels of the "good" HDL cholesterol--in many more people than the low-fat diet did. Another trial found that a Mediterranean diet with up to 35 percent of calories from fat actually led to more weight loss than a low-fat diet, possibly because the Mediterranean one is more filling so people eat less, and more appealing so people adhere to it.
  
  
• Stick with whole foods. They're loaded with phytochemicals, nutrients, and other beneficial substances, which often work better in combination with other food components. In contrast, studies of isolated antioxidant supplements have generally found no benefit.
  
  
• Choose bright colors. Vivid fruits and vegetables tend to be rich in phytochemicals that have antioxidant and antiinflammatory properties. "Including a variety of bright colors in your daily diet can help counteract the effects of aging," says neuroscientist James Joseph, Ph.D., of the USDA Human Nutrition Research Center on Aging at Tufts University. Joseph has shown that feeding concentrates of blueberries and other colorful produce to aging rats improves cognitive and motor function--results similar to those in calorically restricted animals.