Older people who can't read have a greater chance of dying, including from cardiovascular disease, a U.S. study released Monday suggests.

The study, published in the Archives of Internal Medicine, investigated 3,260 U.S. patients over 65 who were on medicare. It indicates that older adults with low literacy levels had a 50 per cent higher mortality rate compared to seniors with better literacy skills.

"The excess number of deaths among people with low literacy was huge. The magnitude of this shocked us," lead author Dr. David Baker, who worked on study with his colleagues from Northwestern University's Feinberg School of Medicine, said in a news release.

Cardiovascular disease was cited in the study as the most common cause of death among those with "inadequate health literacy." The study showed that low health literacy was the top predictor of mortality after smoking, also surpassing income and years of education.   

Northwestern began the study in 1997, with study participants from Cleveland, Tampa, Miami and San Antonio.

At the time, participants were asked a variety of personal questions on many areas, such as medical background, education and health behaviours. They were also asked to complete a literacy test where they had to read a variety of health-related materials, such as pill bottles, that required understanding numbers.

After the project began and the interviews were completed, researchers determined which participants had died after six years. 

"There are several possible mechanisms by which the association between literacy and mortality might occur," the study says. "Inadequate health literacy is associated with less knowledge of chronic disease and worse self-management skills for patients with hypertension, diabetes mellitus, asthma and heart failure."

Baker said: "When patients can't read, they are not able to do the things necessary to stay healthy. They don't know how to take their medications correctly, they don't understand when to seek medical care, and they don't know how to care for their diseases."

Baker added that more plain language is needed. 

"We're not talking about dumbing down material. We're talking about using simple language the average person would understand."

He said he would like to banish medical jargon and simplify language, for example, saying "sugar" instead of "glucose" when discussing diabetes.

Forty per cent of Canadians aged 16 to 65 and representing nine million Canadians struggle with low literacy, according to a 2005 survey on Adult Literacy and Life Skills by Statistics Canada and the Organization for Economic Co-operation and Development.