In what looks like a jolt to the dream of retiring early, epidemiologists have found that workers who quit at age 55 face a significantly higher risk of dying in the following decade.

The study of more than 3,500 Shell Oil workers who retired between 1973 and 2003 found no increased death rate for those who retired at age 60 or 65, according to a report in the Oct. 22 issue of the British Medical Journal.

Shell Oil did not make available the epidemiologists who did the study. A statement released by a company spokesperson said the study was "part of Shell's routine monitoring of its workforce." Shell has followed its retirees for as long as 26 years.

"There is a widespread perception that early retirement is associated with longer life expectancy, and that retiring later leads to early death," the researchers wrote. "The possible health benefits of retirement, such as reduced role demand and more relaxed lifestyle, have been postulated to improve longevity among people who retire early."

Not so, the study found. The death rate for workers who retired at 55 was 37 percent higher than for those who kept working until 65.

The company statement had a prosaic explanation for the higher death rate. "For those who retire at 55, the most likely explanation for the less favorable health outcome is a preexisting health condition at the time of retirement," it said.

"I would agree with that," said Dr. Jack Guralnik, chief of the National Institute of Aging's Laboratory of Epidemiology, Demography and Biometry.

The report said an effort was made to "reduce potential bias due to differences in health status between early and late (age 65) retirees." But, Guralnik said, "In a group like this, retiring at age 55, a substantial number of those people are retiring for health reasons."

The report itself barely hinted at such a cause.

"Although the effect of early retirement because of failing health may not be totally eliminated, survival rates remained significantly greater for those who retired at age 65 compared with those who retired at age 55," the researchers wrote.

Health has an inevitable effect on survival, said Colin Milner, chief executive officer of the International Council on Active Aging, in Vancouver, Canada. But many people underestimate the importance of their job when they give it up, he added.

"We tend to build our lives around our work," Milner said. "When we are no longer working, we can lapse into lack of activity, and that can contribute to bad health."

To be healthy, retirement must be active, Milner said. In his experience, he said, retired people who plunged into new activities enjoyed their lives more, and were thus healthier. One study showed "that older adults who volunteer to help others can reduce their risk of risk of dying prematurely by 60 percent," he said.

The Shell study included such factors as socioeconomic status -- those who retired from low-paying jobs had a higher death rate than better-paid workers -- but it did not make any mention of the possible effect of post-retirement activity.

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