Better medicine, an emphasis on clean living and spirituality are all contributing to making older Americans the healthiest humans at their age in the history of the world, argue two University of California, Davis, human-development scholars in a new book.

"What jumps out at you, after reviewing all the studies, is that people who watch their nutrition, avoid toxins like cigarettes or alcohol in excess, and who exercise are living long, healthy lives," says Carolyn Aldwin, co-author of "Health, Illness and Optimal Aging: Biological and Psychosocial Perspectives," which was published in July.

Traditionally, people who study healthy aging have said the key ingredients to a long life include maintaining good physical health, being active mentally, having a zest for living, and being integrated into a supportive community of family and friends with regular social activities. However, an essential variable not previously recognized in medical models for aging gracefully is the importance of spirituality, Aldwin and co-author Diane Gilmer say.

"We've also found a huge difference in mental health and well being among people depending on how they spiritually cope with their own diseases, pain and losses in later life," Aldwin says. She says this inner strength can be found through organized religion as well as from meditation and the spirituality and wisdom gained through a long life.

In the book, Aldwin, a specialist in adult development and aging, and Gilmer, a public-health nurse and gerontologist, examine a large array of national studies that have analyzed how aging affects health and illness. By integrating knowledge of how human psychology and sociology interact with biology, the authors say their book can help gerontologists, psychologists and other professionals advise their patients on how to live happy, healthy, long lives.

"We're finding that people are living a much longer time with fewer disabilities," Gilmer says. "Thanks to medical advances, we treat diseases better by helping people adapt more rapidly."

"We found that some people, who have been followed over the past 20 years starting in midlife, have shown little or no changes in their physical health -- they really haven't aged very much," Aldwin adds.

Members of the World War II generation, now in their 70s and 80s, are the beneficiaries of burgeoning medical knowledge gained over the past half century, Gilmer points out. For instance, unlike the past practice of keeping people with fractured hips in traction for two weeks, nowadays doctors urge their patients to be up and moving within 24 hours after surgery. The patients are discharged to a skilled-nursing home within three to five days where rehabilitation begins almost immediately. As a result, people are recovering more quickly with fewer long-term health problems.

Many in the next younger generation, baby boomers, are also aging better than people in their age bracket during previous eras, but Gilmer and Aldwin see a troubling class and educational divide. People with more resources are able to find the leisure time to exercise regularly, pay for smoking cessation classes or afford more expensive health treatments, for instance.

"We also found that a college education was very important to optimal aging," Aldwin says. College-educated Americans are more knowledgeable about good health habits and tend to be more motivated to adopt them.

On the other hand, Americans are experiencing an epidemic of obesity and its accompanying health issues -- diabetes, heart problems and cancer. All of these diseases activate the aging process, Aldwin points out.

"And, obesity is linked to social class," Aldwin says. "We predict that the baby boomers will see an accelerating class difference in how long they live."

In addition, the baby boomers are in the first generation to experience high levels of divorce and delayed child-bearing. Divorce often contributes to breaking down support networks that help people cope with other life problems. Having children later in life offers higher risks for breast cancer and hypertension, Gilmer says.

In this major review of health studies, Aldwin and Gilmer found that people's personalities impact their health. While emotional stability appears to be protective of health, hostility is as much a risk factor as smoking for heart disease in people during their 40s, Aldwin says. Anxiety, which can be associated with the heart suddenly stopping, is also a personality health risk.

The increase in anxiety over the past two decades may also be a cause for concern, given the role of anxiety in cardiovascular health. "Highly anxious women who don't work outside the home have an eight-fold risk of sudden death," Aldwin says.

Regardless of class, however, all of us are physiologically 10 to 15 years younger than our parents were at our age, Gilmer and Aldwin say, due to the dramatic improvement in overall health during the past quarter century.

An expert on stress and coping, Aldwin has been gleaning insights about optimal aging from two longitudinal studies during her career. Since 1985, she has worked with the Normative Aging Study in Boston, which has followed more than 2,000 male veterans over the past four decades. For 13 years, she also has directed the Davis Longitudinal Study, which examines aging and other issues among various UC Davis graduating classes since 1967.

A former nurse practitioner for the elderly, Gilmer studies and teaches about the physical aspects of aging, including chronic diseases and disabilities, as well as about care giving.