"We've always known personal income and education can affect one's health outcomes," said Esme Fuller-Thomson, study co-author and assistant professor of social work at the University of Toronto. "What we didn't know until now was the substantial strength of the relationship between state-level income inequality and disability."

The research, Fuller-Thomson said, shows "individuals have a higher likelihood of physical disability when they live in states where wealth is distributed very unevenly."

In states with greater income inequality, the rich were also at a disadvantage, researchers said. Both rich and poor people were more likely to have high-level disabilities affecting tasks such as dressing, bathing and mobility, than people living in states where income was distributed more equally.

Fuller-Thomson and Tahany Gadalla, study co-author and assistant professor of social work at the university, examined information collected from 645,000 Americans through the 2003 American Community Survey.

Their findings are published in the November issue of the British journal Public Health.