Advice on Making Most of Getting Old : Lifestyles: Authors write a guidebook to understanding the physiological effects of aging.

Recovering one’s youth may be a universal pursuit, but the reality is that people get older.

In making that reality the basis for “Aging Well,” authors Thomas Hager and Lauren Kessler have produced a lifestyle guidebook for anyone over 20.

Yes, over 20.

“We start to age the second we’re born,” Kessler said. “The aging and dying of cells in our body is constant. A 20-year-old or 30-year-old thinks they’re immortal, but in fact, that person is in the process of aging.”

Hager and Kessler describe the physiological effects of aging on the body in detail, from bone loss to the shrinking size of the brain.

“We did as complete a survey as is humanly possible of the medical literature, meaning what was published in medical journals in the last 20 years and the scientific papers that came out of conferences,” Kessler said.

It took the couple a year to gather, read and evaluate the research. The manuscript was reviewed by a team of doctors.

There are many fad books on the market full of “quack stuff, strange diets, miracle foods,” Kessler said. “The whole focus of those books is that you should fight aging, that someday we’ll find a miracle cure for this aging.”

Hager and Kessler suggest aging might not be so bad. In fact, many conditions thought to be the normal trappings of old age can be traced to environment and lifestyle: inactivity and bad habits.

“Do you say: ‘Lots of wrinkles and lines and bags are a natural part of aging?’ Another way of looking at it is: ‘What percentage of the aging of skin has to do with overexposure to the sun?”’ Kessler said. “That’s not aging. That’s damage that we cause ourselves.”

The book describes the normal effects of aging: Your hair becomes drier and gray, your skin wrinkles and loses pigment, your hearing becomes less acute, your spine compresses, your immune system doesn’t fight as well, your brain mass shrinks.

But there is no reason for your joints to stiffen or hurt unless you have arthritis or are inactive. And heart disease is caused not solely by age, but rather by a combination of poor diet and inactivity and is promoted by habits such as smoking.

“I would hope to empower people with the book, to make them understand that much of the aging process is within their power to control,” Kessler said.

Basically, if you live well, you’ll age well. If you have healthy habits, you’ll have a better chance of staying healthy as you grow older.

It is plain good sense that you have heard before: Stop smoking, don’t abuse alcohol, stay out of the sun, turn the volume down on your stereo, brush and floss your teeth daily, stay on a proper diet and get plenty of rest and exercise.

“Personally, I think that it’s not nutrition, but exercise that is the one thing that we discovered that has the most impact on aging well,” Kessler said. “If you had to choose what to do, that would be my No. 1. choice.”

Kessler, 40, is an author and journalism professor at the University of Oregon in Eugene. Her husband Hager, 37, is a free-lance writer on medical topics and edits the university magazine Old Oregon.

The couple started talking about the concept after Hager’s 30th birthday.

“It was born of a number of specific conversations over a period of a few years that had to do with the kind of interests anybody has about growing older,” Kessler said.