You might have noticed that TV weatherman Willard Scott's morning roll call of people celebrating 100-plus years on the planet seems to grow longer and longer.
According to the U.S. Census, the number of American centenarians has roughly doubled in the past 20 years to about 72,000 and is projected to at least double again by 2020. (The same experts, however, also say that that might be a conservative guess.)
Linda Van Eldik, director of the Sanders-Brown Center on Aging at the University of Kentucky, said several factors have contributed to the longevity.
First, Americans as a whole are living longer. The average life expectancy has gone from 49 at the turn of the 20th century to 78 in 2012.
Also, she said, medical advances have made it possible to routinely cure diseases that once were fatal.
Van Eldik said there appear to be some common traits among those who live the longest. Many of them, she said, "follow a series of good health habits" such as exercising and eating a balanced diet.
She said a positive personality seems to be another common thread.
"They seem to have an increased level of happiness," she said. That doesn't mean that life has not thrown centenarians their share of tough times. But, she said, they seem to have an ability to come back after difficulties with a continued positive outlook.