About one in 10,000 people seems to be a "slow ager" who lives to 100 -- sometimes even in spite of bad health habits, like smoking or exercising little, according to new research. Will you be among them? You won't know if you're among the genetically predisposed for sure, of course, until those 100 birthday candles are lit. But researchers are discovering more and more clues as to who's on his or her way.
Clue #1: How many elderly relatives are on your family tree?
What it may mean: You may have longevity genes.
At least half of all those who reach 100 have a parent, sibling, or grandparent who has also achieved very old age (90-plus), according to the New England Centenarian Study at the Boston University School of Medicine, which studies 100-plussers to unlock secrets of successful aging.
A 2002 study by the center's director, geriatrician Thomas Perls, found that male siblings of centenarians have a 17 times greater chance of reaching their 100th birthday than other men born around the same time; female siblings are 8.5 times more likely to hit 100 than other females also born around the same time.
Other studies have found that exceptional aging is often clustered among multiple first-tier family members, supporting a genetic link. Having siblings, parents, and grandparents who make it to 100 seems to be a much stronger indicator than counting cousins and other more distant relatives.
Clue #2: How fast and how far can you walk?
What it may mean: You're in good condition for the long haul.
Faster walkers live longer. University of Pittsburgh researchers crunched numbers from nine different studies including almost 35,000 subjects ages 65 or older. The result: For each gait speed increase of 0.1 meters per second came a corresponding 12 percent decrease in the risk of death.
The average speed was 3 feet per second (about two miles an hour). Those who walked slower than 2 feet per second (1.36 miles per hour) had an increased risk of dying. Those who walked faster than 3.3 feet per second (2.25 miles per hour) or faster survived longer than would be predicted simply by age or gender.
A 2006 report in the Journal of the American Medical Association found that among adults ages 70 to 79, those who couldn't walk a quarter mile were less likely to be alive six years later. They were also more likely to suffer illness and disability before death. An earlier study of men ages 71 to 93 found that those who could walk two miles a day had half the risk of heart attack of those who could walk only a quarter mile or less.
Clue #3: Do you have a lot of people in your life?
What it may mean: Social engagement is a key lifespan-extender.
Countless studies have found that social isolation is bad for your health, while having friends and social engagement is good. One of the more surprising findings in The Longevity Project (a book about an eight-decade study of 1,500 subjects all born around 1910) is that religious women lived longer -- primarily, as it turned out, because of the social connectedness of their faith-based lifestyle. That is, they worshipped with others, joined committees, and engaged in social outreach, from clothing drives to soup kitchens.
"There was a clear, similar trend among people who had civic engagements, were active in their communities, volunteered, and otherwise stayed connected, whether with families, friends, or coworkers," says Leslie R. Martin, a professor of psychology at La Sierra University in Riverside, California, who's the coauthor of The Longevity Project.
Clue #4: Are you a woman?
What it may mean: Odds are more in your favor from the start.
Sorry, fellas. In 2010, there were 80,000 centenarians in the U.S.; 85 percent of them were women, and only 15 percent were men.
It's not entirely clear what's causing the disparity. Theories include the protective role of female sex hormones and menstruation, lower rates of cardiovascular disease for women, and higher smoking rates among men. Men also have higher rates of car accidents and suicide.
The survival gap is gradually narrowing, however, possibly because women are living lives that are conventionally male in terms of stress and poorer health habits, especially smoking.
One bit of good news for men: Those who do reach the century mark are, on average, healthier and more functionally fit than their female counterparts. Women survive medical catastrophes better than men but with more disability.
Clue #5 (for women only): Did you have a child after age 35?
What it may mean: This is possible evidence that you're a slow ager.
Popular wisdom holds that late-life babies are tougher on a mother's aging body. If so, that graying hair mixed with newborn pink or blue reflects a silver lining: According to the New England Centenarian Study, a woman who naturally conceives and bears a child after the age of 40 has a four times greater chance of living to 100 than women who don't. Moms who give birth naturally at 35-plus also make it to 100 in larger numbers than younger counterparts.
It's not the act of bearing a child late in life that extends lifespan, however. Researchers instead believe that being able to conceive and give birth in your late 30s or 40s is probably an indicator that your reproductive system is aging slowly -- and that therefore the rest of your body is likely to be aging slowly, as well.
Clue #6: When were you born?
What it may mean: Growing lifespans give younger people an edge.
A 2011 report by the British Department for Work and Pensions estimated life expectancy for citizens at various ages, providing a snapshot that Yanks can learn from, too.
A British girl born this year has a one in three chance of living to 100; a 2011-born boy has a one in four chance. If you're a 20-year-old woman, you have a 26.6 percent chance; a 20-year-old man has a 19.5 percent chance.
The average 50-year-old woman in the U.K. has a 14.6 percent chance of seeing 2061, the year of her diamond-anniversary birthday; just over one in 10 of her male counterparts will still be around then.
And if you're 99 now? You have a whopping 67 percent chance of seeing another year.
Clue #7: Do you worry -- but not too much?
What it may mean: There's a "healthy" worry level.
It sounds like a punch line: "Be afraid, be very afraid -- but not too much!" So-called "catastrophizers" -- Eeyore-like personalities who fret about impending doom, see the glass as half-empty, and are harshly self-critical -- tend to die sooner, according to psychology professor Leslie R. Martin of La Sierra University.
On the other hand, a moderate amount of anxiety and worry is associated with a 50-percent decreased risk of death in any given year, she says. Moderate worriers tend to be less impulsive, take fewer risks, have less risky hobbies, and plan for alternatives, which may all be protective without adding a negative health impact.
More clues that you could live to 100
Clue #8: Is your weight normal -- or are you only slightly overweight?
What it may mean: You have better odds of reaching 100 than if you were obese.
A surprising 2011 Albert Einstein College of Medicine study of 477 adults ages 95 to 112 found that these solid-gold agers had no better health habits overall than a comparison group born at the same time that had been studied in the 1970s. One difference: Those in long-lived group were much less likely to be obese.
Both male and female centenarians in the study were overweight at about the same rates as those in the shorter-lived group. But only 4.5 percent of the long-lived men and 9.6 of the women were obese, compared to 12.1 percent and 16.2 percent, respectively, of the younger-lived controls. ("Normal weight" is a Body Mass Index -- or BMI, a measure of height in proportion to weight -- in the range of 18 to 24; "overweight" is 25 to 30; over 30 is "obese.")
This finding echoes other studies showing the greatest risks of death among those who are obese or underweight at age 65 (BMI under 18.5), compared to those of normal weight or slight overweight. A 2011 study at Loma Linda University in Southern California found that men over age 75 with a BMI over 27.4 lived nearly four years less than those with a lower BMI. For women over age 75, a BMI over 27.4 led to a two-year shorter lifespan. Studies of centenarians show that men who reach 100 are almost always lean (more so than women).
Luckily, this clue is one you can control. "Since you can't be sure if you'll live to 100, I wouldn't take the chance of ignoring the lifestyle interventions that we know will at least put you in the half the population who die after age 80 -- starting with watching weight and being sure to exercise," says the senior author of the Albert Einstein study, Nir Barzilai, director of the college's Institute for Aging Research.
Clue # 9: How long are your telomeres?
What it may mean: Many people who live to 100 have a hyperactive version of an enzyme that rebuilds telomeres.
"What-o-meres?" you ask. Telomeres are protective DNA sequences at the ends of chromosomes that gradually shorten as cells divide. (Pioneering telomere researcher Elizabeth Blackburn of the University of California-San Francisco compares them to shoelace caps.) Eventually the telomeres become so short that cells stop dividing, a condition called senescence, creating the effects we recognize as aging in related tissue.
Scientists are still unraveling the key role telomeres seem to play in aging, cancer, and other biological processes, but this much is clear: The longer your telomeres, the more time you're apt to have left. A 2010 Italian study reported that cancer-free people with shorter telomeres were more likely to develop cancer within ten years than those with longer telomeres, for example.
Some studies show that removing chronic stress, not smoking, and eating a diet rich in omega-3 fatty acids can improve telomere length. Those centenarians with hyperactive telomere-making apparatus can probably thank their genes, though.
New blood tests are now being marketed directly to consumers, purporting to predict longevity based on telomere length. But critics caution that there aren't standards for measuring telomere length and that there can be such variability in telomeres that it's hard to predict much of anything from a sample.
Clue #10: Are you a positive person?
What it may mean: Emotion influences health, which influences aging.
Some studies have shown that an upbeat attitude about aging adds years. But long-term studies conducted at the Stanford Longevity Center show that emotions, more than attitudes, may be the biologic mechanism at work, says Laura Carstensen, the center's director.
"What's the mechanism at work here? Feeling upbeat about your life means you experience less stress, which in turn affects cortisol levels, which can affect health," she says. Stanford researchers periodically assess 19 different emotions in subjects randomly polled over 1 week at 5-year intervals. Having more positive emotions than negative ones is associated with living longer.
Carstensen is a firm believer that while "slow agers" clearly exist, there's more to their stories than lucky genes. "There's mounting evidence that genes play a role in longevity, but genes play a role in almost everything," she says. "They don't express themselves in vacuums -- there are very complex interactions between genes and lifestyle." So all that advice on how to live to 100? Can't hurt to heed it.