Study co-authors David Cutler of Harvard University and Ellen Meara of Harvard Medical School said much attention has been paid to mortality rates based on socio-economic status, but not education.

Meara and Cutler combined death certificate data with census population estimates and data from the National Longitudinal Mortality Study.

The study, published in the March/April edition of the journal Health Affairs, found that for both data sets, life expectancy rose for individuals who had more than 12 years of education and for those with 12 years or less, it plateaued.

For example, comparing the 1980s to the 1990s, better educated individuals experienced nearly a year and a half of increased life expectancy, while the less educated experienced only half a year. For 1990-2000, life expectancy rose an additional 1.6 years for better educated, while remaining fixed for the less educated.

"Although improvements in health often occur more rapidly within some groups than others, it is surprising that life expectancy remained so flat for the less educated," Meara said in a statement.