The U.S. division of Sun Life Financial has released the latest edition of its Unretirement Index, which finds that 54 percent of American workers will delay their retirement by at least one year due to the current economic situation.

Of those delaying retirement, 24 percent saying they will need to work more than five years. The Index, released multiple times a year, gauges how economic, financial and societal forces affect working Americans, and forecasts their future retirement decisions that will impact individuals, the government, employers and the broader economy.

The Unretirement Index most recently polled workers in December, and previously polled them in August. As a result, the latest findings are the first to measure how American attitudes and expectations of retirement have changed since the economic crisis last fall.

Sun Life’s ongoing research showed the current economic climate has adversely impacted the American workforce, and while the number of Americans who expect to work at least 20 hours a week after age 67 is largely unchanged, their reasons for continuing to work have dramatically changed. Over the last 90 days, the most popular reason cited by American workers for why they would continue to work past the traditional retirement age of 67 shifted from "to stay mentally engaged" to "earn enough money to live well."

Unretirement is defined as working at least 20 hours per week after the age when one is eligible to receive Social Security benefits. Sun Life created this Index to learn more about the reasons why Americans are choosing to "unretire," the company said in a statement.