The ranks of the nation’s oldest residents are growing quickly now that people who reach age 90 are expected to live longer than ever before, according to a study released on Thursday.

The number of Americans age 90 and older nearly tripled in the past three decades, to the current 1.9 million from 720,000 in 1980, said a report from the U.S. Census Bureau.

That number may reach 9 million by 2050, according to the report titled “90+ in the United States: 2006-2008.”

“I think it’s going to grow even faster than predicted in the report,” said Richard Suzman, director of behavioral and social research at the National Institute on Aging, which commissioned the study.

More folks over the age of 90 means increased stress on pension and retirement funds, health care costs and caretaker relationships with younger generations, the study said.

A person who makes it to 90 years old today is expected to live almost another five years, the study said. And, a person who lives to celebrate a 100th birthday is likely to live another 2.3 years.

An increase in education, improvements to nutrition and public health, a decline in smoking, diabetes controls and a reduction in strokes have been major factors contributing to the aging boom, Suzman said.

The report, which details the demographic, health and economic status of the oldest Americans, is based on the 2006- 2008 American Community Survey. It was released on the U.S. Census Bureau website.

“This is very important data for policy makers and researchers to start considering whether to change the definition for oldest-old from 85 to 90-plus,” said Wan He, a Census Bureau demographer and an author on the report.

The so-called “oldest-old” in the United States has generally been defined as 85 and older.

Given the aging boom and increased life expectancy, that marker may now be inching closer to 90, researchers said, and it’s important to understand the differences among the older population.

For example, of people aged 85-89, about 69 percent reportedly have a disability, which might include trouble hearing or seeing or a physical limitation.

At ages 90-94, that number jumps to nearly 83 percent.

Other study findings showed that the 90-plus population in the United States is overwhelmingly white with most earning a high school diploma.

Education is linked to a number of factors related to a person’s well-being, according to the report, with higher education linked to lower mortality rates and better overall health.

Women over the age of 90 outnumbered men by nearly 3 to 1, according to the report. Nearly 80 percent of those women were widowed while more than 40 percent of the men 90 or older are married, it said.

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By Lauren Keiper