Some 90 million Americans have low health literacy but those with limited English and disabilities have even lower health literacy, U.S. researchers said.

Diane Smith of the University of Missouri School of Health Professions said low health literacy is a mismatch between patients' abilities to understand healthcare information and providers' abilities to communicate complex medical information in an understandable manner.

"There is already a problem with low health literacy within the general population," Smith said in a statement. "When looking at populations with disabilities or limited English proficiency, people need to be more conscious that these particular populations may have more difficulty understanding information, such as treatment options or medication instructions, from their physicians."

In the two studies, researchers found patients with disabilities or limited English proficiency often perceived that their physicians did not listen to them, explain treatment options, treat them with respect, spend enough time with them or involve them in the treatment decisions.

In addition to health literacy issues, those with limited English proficiency had significantly reduced access to healthcare. Few doctors have multi-lingual backgrounds -- especially in rural areas -- and it can be difficult to find a provider who can accommodate limited English proficiency patients, the researchers said.

The findings were published in the Disability and Health Journal and are scheduled to be published in the Journal of Healthcare Disparities Research and Practice.