It's no secret that over the last few decades, life expectancy has been rising. However, recent data shows that not everyone has benefited from this encouraging trend. New findings from Harvard Medical School and Harvard University demonstrate that individuals with more than 12 years of education have significantly longer life expectancy than those who never went beyond high school.

“We like to think that as we as a country get healthier, everyone benefits,” says David Cutler, dean for social sciences at the Faculty of Arts and Sciences at Harvard University, and study co-author. “Here we’ve found that you can have a rising tide that only lifts half the boats—and the ones lifted are the ones doing better to begin with.”

The research, which was conducted by Cutler and Ellen Meara, assistant professor of health care policy at Harvard Medical School, appears in the March/April edition of the journal Health Affairs.

Over the years, much attention has been paid to mortality rates based on socio-economic status, but less attention has been paid to recent trends in life expectancy, mortality, and education level. To understand recent mortality trends, Meara and Cutler combined death certificate data with census population estimates and data from the National Longitudinal Mortality Study. Restricting analyses to whites and non-Hispanic blacks, the team created two separate data sets, one covering 1981-1988, and the other 1990-2000.

In both data sets, life expectancy rose for individuals who had more than 12 years of education. 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.

In addition, when the data was broken down by gender, the researchers found that women fared worse than men. Less educated women, regardless of race, experienced a slight decline in life expectancy at age 25.

Overall in the groups studied, as of 2000, better educated at age 25 could expect to live to age 82; for less educated, 75.

“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 during periods when others enjoyed dramatic gains in longevity,” says Meara.

The researchers found that much of the mortality gap can be attributed to smoking related illnesses. Just two diseases usually caused by smoking, lung cancer and chronic obstructive pulmonary disorder (which comprises chronic bronchitis and emphysema), account for 20 percent of growing mortality differences in the 1990s. Many other illnesses like heart disease and other types of cancer, also count smoking as contributing factors. The importance of smoking is not surprising, since other data has shown that the less educated have not given up smoking to the same extent that those with more education have. (Other causes of death examined were diseases of the heart, non-lung cancers, stroke, and unintentional injuries.)

“There’s a bit of complacency in the fact that year after year lifespan goes up,” says Cutler. “Our data shows us that we need to start thinking about doing much more for the groups at the bottom if we don’t want to see these gaps grow.”