Gwen Weiss-Numeroff's fear of illness and loss began when she was only 8, after the person closest to her in the world -- her big brother Steven -- died of leukemia at the age of 9. That fear only intensified in her 20s after her Uncle Jerry died of a heart attack at 48. His daughter -- her cousin -- died a few years later at age 28. When Weiss-Numeroff hit her 30s, her best friend Tammy died of breast cancer at age 33.

"The final straw was when I was 45, three years ago," Weiss-Numeroff, a nutritionist, said. "My mother fell ill from ovarian cancer at 70. Doctors diagnosed it just three weeks before she died."

Feeling as though she had a dark cloud hanging over her, Weiss-Numeroff decided to look for some answers to find out if she was doomed by her genetics and destined to die young. "I decided that I wanted to know how people in this country live so long ... and how they live to be healthy at 100," she said. "I wanted to meet these people to see if there's hope. I have always feared aging. My mom fell into a depression the last five years of her life.

"I wanted to know how people stay busy and happy and healthy even to the age of 100 and beyond," she said.

This yearning for answers was the genesis for her book, "Extraordinary Centenarians in America: Their Secrets to Living a Long Vibrant Life," published earlier this month. The book profiles 30 centenarians, who reveal their diet and exercise secrets and discuss how they stay busy, happy and healthy in their 90s and beyond.

Weiss-Numeroff featured Besse Cooper who, at 116, was the oldest person in the world before her death earlier this month. When asked the secret to long life, Cooper said: “Mind your own business and don't eat junk food. Treat everyone the way you want to be treated, work hard and love what you do."

She met Irving Kahn who, at age 106, shows no sign of retiring any time soon. He's still chairman of the investment firm he founded, Kahn Brothers Investment, working five to six hours every day.

"One person just started writing children's books at the age of 99. Another one just got married for the first time at 99," Weiss-Numeroff said. "These people all keep busy and all enjoy what they're doing."

Weiss-Numeroff said that during her research, she was most comforted by the fact that people are not controlled completely by their genetics. "About 80 percent of these centenarians have siblings that died in their 60s or younger," she said. "Genetics definitely play a role but genetics certainly aren't everything."

Weiss-Numeroff said most of the people she interviewed didn't smoke although some were moderate drinkers. "The main thing they all had in common was that they all go with the flow... they have a remarkable ability to adapt to change and that is a huge thing," she said. "They don't sweat the small stuff but they take things on, embrace life and move forward."

According to the most recent Census data, there are almost 62,000 people who have reached 100 living in the United States. Among those in the centenarian club, some 80 percent are women, according to an analysis released Monday of 2010 Census data. When it came to race, whites made up 82.5 percent of the country's centenarians -- even though they made up 72.4 percent of the U.S. population in 2010.

"It's clear you don't have to be doomed by your genetics. The people I talked to seek joy and find joy," Weiss-Numeroff said. "They also were totally outside themselves and always thinking of others, either while acting as caretakers or by volunteering.

"They were always focused on other people," she said. "The do-gooders do seem to have a better and longer life."

Check out our slideshow for more "secrets" to living a long life from the 30 centenarians featured in the book.

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