More people than ever live past 100 years of age. So-called “supercentenarians,” those who reach 110 and beyond, are rising in numbers all over the world, 75 individuals to date and counting.

What are the causes of such extreme longevity and what is different about these ancient folks that lets them outlast normal mortals by decades? A new study tried to find answers by investigating the genetic traits of a small group of participants between the ages of 110 and 116.

By sequencing the genomes of 16 women and one man, all of whom were living in the United States at the time of the study, the researchers hoped to find genetic commonalities that could help explain their extraordinary life spans. Unfortunately, their findings were inconclusive.

“Our hope was that we would find a longevity gene,” said Dr. Stuart Kim, a professor of biology and genetics at Stanford University and lead author of the study report to Reuters. “We were pretty disappointed.”

Regardless of his study’s meager outcome, Dr. Kim remains optimistic that more research will eventually be able to identify genetic causes as the driving force behind longevity.

“This marks the beginning of the search for key genes for extreme longevity,” he said. “These supercentenarians have a different clock where they are staying really highly functional for a long time. We wanted to know what they had. It’s pretty clearly genetic.”

The reason why it is hard to pinpoint specific genetic characteristics that may be responsible for greater life expectancy is that the genetic effects are likely very complex and involve mechanisms in the body that are not yet fully understood, he said.

While experts have long debated whether nature or nurture is ultimately the decisive factor in how well we age, whether some of us are born to last longer or whether diet and lifestyle play a role, it is clear for Dr. Kim that genetic make-up outdoes anything we can add in terms of healthy living. Among the participants in his study he found no especially health-promoting eating or exercise habits. About half of them were even long-time smokers.

Also, there is no evidence that the achievements of modern medicine are extending the maximum life span today’s humans can hope for in comparison to their ancestors, according to Dr. Leonard Hayflick, a professor of anatomy at the University of California, San Francisco and author of the gerontology classic, titled “How and Why We Age” (Ballantine Books 1994).

What advances in medical science have produced, however, is a greater possibility to delay the effects of illnesses commonly associated with old age.

Both social changes like greater hygiene, reduced rates of smoking, better diet and other personal health and lifestyle choices, as well as medical intervention have increased for many more people the number of years they enjoy in good health and vigor and decreased the time spent in illness and decline. This phenomenon is known as “compression” because it compresses age-related susceptibility to diseases into a shorter period. It is that growing vulnerability and lessening strength to fend off illnesses that make us become more frail and eventually succumb.

And here is where nurturing can help us to fare better. By adhering to a healthy diet, controlling weight, exercising regularly, getting enough sleep, managing stress, and so forth, we are indeed able to fortify our natural defenses and, as Dr. Kim suspects, slow down the clock.

Timi Gustafson R.D. is a registered dietitian, newspaper columnist, blogger and author of the book “The Healthy Diner – How to Eat Right and Still Have Fun”®, which is available on her blog and at amazon.com.  For more articles on nutrition, health and lifestyle, visit her blog, “Food and Health with Timi Gustafson R.D.” (www.timigustafson.com). You can follow Timi on Twitter, on Facebook, and Google+.