Excerpt from Real Age by Michael F. Roizen M.D., plus links to reviews, author biography & more

Telling him to quit smoking didn't work. (Quite literally, I called him every single day for years to ask him if he had quit yet. The answer was always "no.")

"Simon," I said one day when he was in for a checkup, "how old are you?"

"Mike, please," he grumbled. "You know I'm forty-nine."

"Simon, this isn't a joke," I replied. "How old are you really?"

"What are you getting at?" he said, eyeing me suspiciously.

"Did you know that all that smoking has made you older?" I asked him. "Eight years older. Right now, you may be forty-nine. But your body is as old as someone who is fifty-seven, maybe more. For all practical purposes, your age is fifty-seven."

"I can't be fifty-seven," he said.

"Why not?" I asked.

"Because no man in my family has ever lived to the age of fifty-eight."

The message hit home. Simon quit smoking. He began exercising and eating right. He reduced his RealAge and began celebrating "year-younger" parties, rather than his usual "one-more-year-over-the-hill" birthday parties. Over time, he became younger.

Fundamental to economics is the concept of "net present value." Net present value is used by economists to determine the current value of investments that have future payoffs. The RealAge concept allows us to calculate the value of different types of health behaviors and choices. In biologic terms, the difference between your calendar age and your RealAge is a calculation of the net present value of your health behaviors; it is the estimate of what age you are physiologically when compared with the rest of the population.

RealAge. Copyright (c) 1999 by Michael Roizen. Reprinted with permission from HarperCollins Publishers, Inc. All rights reserved.