People who have trouble reading health information have worse general physical and mental health than those who process it easily, reports a study in this week's Archives of Internal Medicine.

Health literacy, the ability to understand health information, has previously been connected to delayed diagnoses, less adherence to medical directions, and the inability to understand one's disease. This is the first large study to show a relationship between literacy and health.

The authors found that though people with low literacy don't engage in riskier health behaviors than other people, they do have a higher risk of developing certain diseases, such as diabetes and heart failure. These two diseases are often greatly affected by patient management in the early stages of the disease.

"We think that health literacy is not likely to have an impact on your getting a disease so much as on your managing the disease once you have it," says lead author Michael Wolf of Northwestern University's Feinberg School of Medicine.

The researchers interviewed nearly 3,000 new Medicare enrollees in Ohio, Texas, and Florida. They tested them on their ability to read federal health information and on their practical knowledge with questions such as, "If you are supposed to take a pill every six hours and took one dose at 7 a.m., when should you take the next dose?" Then, they asked the patients about both their physical and mental health.

The problem of health literacy very likely extends beyond those categorized in this study as health illiterate, says Wolf. "If you don't have a medical degree or are not well versed in medical terms, a lot of the information we distribute is very confusing." Even those with high levels of education and literacy often find health information confusing, he says.

But the problem may be compounded among those with low levels. People who haven't attained some of society's basic achievements, such as graduating from high school or learning to read, may have more shame than others, says Wolf. They don't ask their doctor questions or speak up when they don't understand.