I thought it fitting to write my 100th hub about centenarians.

Centenarians are those of us who live to be 100 years old or more. What I found when researching this topic is that this is one of the fastest growing age groups of the American population according to a study done in 2005. Centenarians are growing over 4% a year a having already seen a 51% increase from 1990 to 2000.

I'd like to share some of the interesting pieces of this 81 page document that was a Research Project sponsored by the Society of Actuaries Committee on Life Insurance Research entitled "Living to 100 and Beyond: Search for Predictors of Exceptional Human Longevity. Click here to read this study for yourself.

• Specifically, the study focused on the availability and quality of computerized online genealogies of long-lived individuals and then cross-checking them with other internet resources such as the Social Security Administration (SSA) Death Master File (DMF) and the early U.S. censuses. This allowed them to isolate 991 alleged centenarians born in the United States from 1875-1899.

• This report presents some preliminary studies on predictors of exceptional human logevity, including familial factors and early-life livng conditions. There study suggests a link between exceptional longevity and a person' birth order. They found that first-born daughters are three times more likely to survive to age 100, compared to later-born daughters of higher birth orders (7+). First-born sons are twice more likely to become centenarians compared to sons having birth order between four and six. There is also a profound sex difference in the effects of birth order on human longevity. For sons, this dependence has an unusual U-shaped form, with highest longevity chances for both the first-born and the last-born (9+) sons.

• The comparison of households where children -(future centenarians) were raised (using data obtained through linkage of genealogies to early U.S. censuses) with control households drawn from the Integrated Public Use Microdata Series (IPUMS) for the 1900 U.S. census suggests that a farm background (farm ownership by parents in particular) and child residence in the Western region in the United States may be predictive for subsequent survival to age 100. These findings are consistent with the hypothesis that lower burden of sickness during childhood (expressed as lower child mortality in families of farm owners and families living in the West) may have far-reaching consequences for survival to extreme old ages.

• It also was found that life expectancy at age 80 depends on the month of a person's birth: individuals born in January live longer lives than persons born in other months and in April-June in particular. This periodicity repeats in every studied birth cohort starting from birth year 1885 to 1899. However, by age 100 this dependence of survival on month of birth fades out, indicating that centenarians indeed represent a selected population.

In a nutshell, if you're the first-born girl born in January, growing up on a farm in the American West, you've got a good shot at this 100th birthday gig.

Another study, found here, indicates that

"by 2050, according to midrange projections, there could be over 800,000 Americans who celebrate the century mark. Studies show the same trend in other industrialized countries and recently in China. Indeed, demographers are now counting the number of supercentenarians, people age 110 and over."

A 1999 book entitled "Living to 100" by Thomas T. Perls mentions these characteristics that centenaries don't have:

• They don't smoke or drink heavily. Those who had smoked didn't do so for long.
• They gained little or no weight during adulthood. Being overweight makes people more vulnerable to many life-threatening illnesses, including heart disease, diabetes, cancer, and stroke.
• They don't overeat. Okinawan centenarians consume 10%-20% fewer calories per day than typical Americans. The elderly Okinawans consume less fat, too (About 26% of their energy intake comes from fat, compared with 30% or more for Americans.)

• They eat many fruits and vegetables. The Okinawans have an average of seven servings a day.

• They get regular physical activity for as long as they are able. Strength-building activities, such as climbing stairs or lifting small weights, are especially beneficial because they help slow the age-related loss of muscle mass.

• They challenge their minds. Stimulating mental activity may help prevent age-related thinking and memory problems by stimulating communication between brain cells. Particularly among elderly men, decreased cognitive performance is strongly associated with mortality.

• They have a positive outlook. Centenarians seem to have personalities that shed stress easily. An inability to control emotional stress has been linked to memory loss and heart disease.

• They are friendly and maintain close ties with family and friends. Not surprisingly, positive relationships are associated with lower rates of depression. And lower rates of depression may result in lower rates of heart disease.

  Many researchers think that people could add up to a decade to their lives if they emulated the centenarians.