People who keep doing some work in their field after they retire may enjoy better physical and mental health than those who stop work completely or switch to another area of work, according to a U.S. study.

Researchers from the University of Maryland said the findings suggest that prospective retirees should consider moving into so-called "bridge employment" as a transition to full retirement.

"In essence, if someone is in a field where part-time work or self-employment is possible, he or she should consider it as they plan for retirement," researcher Dr. Mo Wang, an assistant professor of psychology, told Reuters Health.

For their study, Wang and his colleagues used data on more than 12,000 workers in a U.S. health study begun in 1992. Participants, who were between the ages of 51 and 61 at the outset, were surveyed every two years over a six-year period.

Overall, Wang's team found, people who went into some form of bridge employment reported lower rates of major diseases like high blood pressure, heart disease, diabetes and arthritis during the study period than their counterparts who went straight into full retirement.

The findings were not explained by older age or worse initial health among people who opted for full retirement, the investigators report in the Journal of Occupational Health Psychology.

On top of their better physical health, "bridge" workers also tended to report fewer mental health problems, such as depression.

The same mental health benefits were not seen, however, when retirees took part-time work in other fields -- possibly, Wang said, because many of these people may have taken those jobs out of financial need rather than choice.

He noted that the lack of benefit could also stem from the fact that these retirees had to adjust to an unfamiliar job position or had to make lifestyle changes.

Bridge work, particularly in one's accustomed field, may benefit physical and mental health for a number of reasons, according to Wang.

In general, he explained, such work may help older adults maintain the active lifestyles they had during their careers and decrease any stress they might feel from the transition into retirement.

Wang said when it comes to mental health, for instance, bridge work may help by allowing people to keep some of the "role identity" that they have formed over their careers.

Staying active in general, not only through work, can also benefit retirees' physical health, Wang noted. He added, however, that any mental health benefits are likely to depend on the type of activity -- whether it is something that the person truly enjoys, and that helps ease any stress of moving into retirement.

"These findings," Wang said, "suggest that for retirees and prospective retirees, carefully considering whether to engage in bridge employment -- and if so, what types of bridge employment -- is quite important."