Study co-author Virginia Richardson, a professor of social work at Ohio State University, said the disadvantage for the poor in walking, bathing, eating, dressing and getting in and out of bed snowballs over time and determines when someone elderly needs to be institutionalized.
"The rich stay healthier, while the poor see steeper declines in their health as they age," Richardson said in a statement. "When people can no longer bathe themselves or cook for themselves, that's when they need to be institutionalized."
Richardson co-author Jinhyun Kim, assistant professor at Marywood University, linked health insurance and socioeconomic status -- which includes income and assets -- to people's physical functioning over an extended period of time, using data from the Health and Retirement Study, run by the University of Michigan.
The study, published in the journal Health and Social Care in the Community, involved 6,519 participants -- part of the Health and Retirement Study, which tracked Americans age 50 and older from 1994 to 2006.
In 1994, the researchers found that those with higher income and assets had better functioning for both men and women.
"The more income and assets you have, the slower your health decline will be," Richardson said.
Those who had private health insurance reported fewer problems with physical functioning than those who didn't, the study said.