Older people who have trouble understanding health-related materials are more likely to die than those who are more literate, a recent study found.

Northwestern University’s Feinberg School of Medicine conducted a study from 1997 to 2003 involving 3,260 Medicare beneficiaries in managed care plans. Nearly 40% of those considered medically illiterate died within the six-year study timeframe, compared with 19% of those in the medically literate group. The study appeared in the Archives of Internal Medicine.

Researchers determined the participants’ medical literacy based on their ability to understand appointment slips, prescription labels and instructions on how to prepare for an X-ray. The inability to comprehend medical information and instructions makes it difficult for beneficiaries to manage chronic conditions, which leads to worsening health, lead researcher David Baker said.