EagleTribune.com, North Andover, MA

Mabel Mitchell says she doesn't understand why people make a big deal over her being 103 years old.

Maybe she's right for shrugging off the attention. After all, centenarians are one of the fastest growing segments of the U.S. population..

The U.S. Census Bureau projects that there will be about 834,000 Americans exhaling against birthday cakes with 100 candles or more in 2050.

For the time being, however, Mitchell, of Danville, is among relatively select company. In a country with a population of about 303 million people, she is one of an estimated 79,000 who have reached their 100th birthday.

That's a small number when compared with the forecast for 2050, but a very large one when looking back in time. As recently as 1950, only about 2,300 Americans lived to be 100.

The growing number of centenarians - people who live to be 100 or older - can be more of a good thing or more of a bad thing, depending upon whom you ask, and whom you are talking about.

S. Jay Olshansky, a professor of epidemiology at the University of Illinois at Chicago, says the mental and physical health of the individual is the key factor.

On.one hand,.the future will see a remarkable increase in the number of extremely healthy, mentally vibrant, active centenarians, he said. On the other hand, a similarly dramatic increase will be seen in people who are frail and disabled being kept alive by medical technology, incurring great human and financial costs

Scientists do not know what percentage of the centenarians will represent each group, though researchers are trying to figure that out, Olshansky said.

His primary objective is trying to determine ways to help boost the numbers in the healthy group. He said promising work is being done to determine ways to slow the aging process and thereby ward off disease and maximize healthy years.

Research on animals using genetic manipulation and reduced caloric intake suggest the human body may have switches that affect aging.

"These switches that influence aging are not set in stone, but potentially adjustable," he states in an article he wrote on the topic.

Meanwhile, the debate rages over how long people can - or should - live.

Influencing life expectancy

Olshansky says the main question is if we can push life expectancy beyond the current average of 78 years (about 80 for a woman and 75 for a man) to 100.

Curing cancer would only extend the present life expectancy by 31/2 years, Olshansky said.

Dr. Thomas Perls, a geriatrician at Boston Medical Center and director of The New England Centenarian Study, has been working since 1994 with people who have reached 100 years.

Perls is critical of those who say humans of today can live 200 or more years - and there are those people out there. He says there is no scientific backing for such claims.

"The people who are proposing these incredible life spans are not scientists and they do not know what they are talking about," he said.

His research indicates that the most people of today could expect to live on average is from the early to mid-90s for men and late 90s to 100 for women. To accomplish this would require a national commitment to raise awareness about lifestyles that promote healthy longevity.

Perls said research has shown that lifestyle would need to resemble the way Seventh-Day Adventists live. The religion discourages smoking and drinking alcohol, and encourages regular exercise and a vegetarian diet. The average practicing Seventh-Day Adventist lives to be 88.

In simple terms, Perls said, his centenarian study indicates that "the older you get, the healthier you have been (in your life)."

Why we're getting older

Medical technology such as kidney dialysis and prenatal care have contributed greatly to life expectancy.

When Mitchell was born in 1904, life expectancy was about 49. A significant reason why the number was so low was because many babies died. Today, the parent of a newborn can expect the child to live to be 78.

The decline in old age mortality and the sheer size of the baby boom - 79 million Americans born from 1946 to 1964 - account largely for the projected explosion in centenarians.

Education and income levels have improved, too. People are living smarter, exercising throughout their lives and eating healthier diets.

Like, Mitchell, most centenarians have been smoke free. (As a youngster, she pilfered one from her brother's jacket, then split it in two, and she and a friend smoked the halves. The tobacco left a bad taste on her tongue and she never became a smoker.)

Also, like Mitchell, most centenarians - about 85 percent - are women.

When men make it to that age, they typically are lean.

Arthur Bradley of Haverhill, 101, stands 5 feet 11 inches tall and weighs about 150 pounds. He says he rarely saw a fat person growing up.

Bradley and Mitchell share some of the character traits common to centenarians, such as humor and the ability to accept change and loss.

Other traits that most centenarians share include a spiritual belief, personal courage and a positive, realistic attitude, said Lynn Peters Adler, J.D., an advocate for older adults and founder of the National Centenarian Awareness Project.

Laurence Kotlikoff, a professor of economics at Boston University and author of the book "The Healthcare Fix," thinks there is a looming crisis when it comes to the cost of caring for the elderly, however. It's a crisis that calls for changes to health insurance, the tax structure and Social Security, he said.

He would not be in favor of denying hip replacement surgery to a very old person who is in pain, but he might question the wisdom of triple bypass surgery for a 95-year-old if that person cannot foot the bill.

Under his proposal, a government board would set policy to define health-care benefits for such a procedure.

Adler is familiar with arguments of those who say it is unwise to spend limited financial resources on the very elderly. But she disagrees with that argument and says people need to take a longer view of life.

"Life is precious," she said. "We owe it to ourselves to maximize whatever life we have."

The New England Centenarian Study

Here are common characteristic of centenarians as reported in The New England Centenarian Study by the Boston University Medical Center:

* Few centenarians are obese. In the case of men, they are nearly always lean.

* Substantial smoking history is rare.

* A preliminary study suggests that centenarians are better able to handle stress than the majority of people.

* Thirty percent of subjects had no significant changes in their thinking abilities.

* Alzheimer's disease was not inevitable. Some centenarians had very healthy brains.

* Many centenarian women have a history of bearing children after the age of 35 years and even 40 years.

* A woman who naturally has a child after the age of 40 has a four times greater chance of living to 100 compared to women who do not.

* At least 50 percent of centenarians have first-degree relatives and/or grandparents who also achieve very old age, and many have exceptionally old siblings.

* Many of the children of centenarians (age range of 65 to 82 years) appear to be following in their parents' footsteps with marked delays in cardiovascular disease, diabetes and overall mortality.

* Exceptional longevity runs strongly in families.

For more on the study, visit http://www.bumc.bu.edu.

Number of projected centenarians among the U.S. population

Year%Population

2000%72,000

2010%131,000

2020%214,000

2030%324,000

2040%447,000

2050%834,000

Source: U.S. Census Bureau