(CBS News) Women may tend to live longer than men but they lag behind them when it comes to gains in life expectancy, according to a new nationwide study from the Institute for Health Metrics and Evaluation (IHME).
The study analyzed county-by-county data from 1989 to 2009. In that time period, life expectancy for men improved by an average of 4.6 years - but for women, it improved by only 2.7 years.
"It's tragic that in a country as wealthy as the United States and with all the medical expertise we have that so many girls will live shorter lives than their mothers," Dr. Ali Mokdad, the head of IHME's research team, said in a written statement.
In 2009, the life expectancy for men ranged from 66.1 to 81.6 years for men and 73.5 to 86.0 years for women. But women across the country were less likely to have had any progress in life expectancy - and many had their lifespans get shorter over time. In 661 counties, life expectancy halted or went backward - compared with 166 counties for men.
The study also highlighted the wide gap between women living the longest lives and those living the shortest. For example, in Collier, Florida, women live 85.8 years on average - but in McDowell, West Virginia, they live an average of 74.1 years. That's an almost 12-year difference.
Although men have a larger gap - 15.5 years - the numbers have changed less since 1989.
What causes these differences in life expectancy? According to the IHME, preventable causes such as tobacco, obesity, high cholesterol and high blood pressure may be to blame. Researchers found the differences in these factors affected the mortality rates of the sexes.
"Women aren't as encouraged by their doctors to get medication to ward off heart disease," Dr. Gina Lundberg, national spokeswoman for the American Heart Association, told USA Today . "And many doctors don't treat their symptoms as aggressively as they do in men. They'll say you have an upset stomach and send you home."
According to the researchers, an estimated 54,000 women's lives could be saved by reducing salt consumption alone.
Differences in health care treatments are another possible reason behind the gap. "What makes the difference is getting the right medication at the right dose," Mokdad said. "We screen people for diseases but don't always follow through to manage the diseases."
Despite the gender gaps, the life expectancy gap between African Americans and white Americans is growing smaller. In 1989, African Americans could expect to live 63.8 years on average, while white Americans had an average lifespan of 72.5 years - a difference of 8.7 years. In 2009, African American male life expectancy improved by nearly a decade to 71.2 years, and white male life expectancy improved at a slower rate to 76.7 years, narrowing the gap to 5.5 years. For women, the gap is even narrower, at 3.6 years. African American women on average in 2009 had a life expectancy of 77.9 years, compared with 81.5 years for white women.
County life expectancy rates can be found on the IHME website.