(Bloomberg) -- We’re living longer and longer. Well, some ofus.

Age 100 is now an imaginable goal for young people aroundthe world with good health care. The average woman in Japanis already living to 87.

Related: 4 trends driving down U.S. lifeexpectancy

Yet many Americans are dying younger and younger. Based onthe latest year of data, the Society of Actuaries last fall droppedits life expectancy estimates for 65-year-olds in the U.S. by sixmonths.

The health of middle-aged non-Hispanic white Americans isdeteriorating fastest.

The result of these trends, according to a new study, is awidening gap between wealthier and poorer Americans. The richest people in the U.S. aren’t just gettingseveral years of extra life, they’re also reaping a financialreward for their longevity – courtesy of the U.S.taxpayer.

These trends will be crucial as the new administration andCongress consider any changes to Social Security, Medicare, and other programs.Even tweaks to these programs, from the retirement age to benefitformulas, could affect the rich and poor very differently.

The researchers, a group of 13 prominent economists and healthpolicy experts , tried to figure out how long Americans can expectto live based on their income, focusing on earnings in midcareer,from 41 to 51, and using Social Security data.

Related: Which is better -- a long life or ahealthy life?

The results are stark. In 1980, a 50-year-old man in thewealthiest fifth of the income distribution could expect to livefive years longer than a 50-year-old man in the lowest-incomegroup. By 2010, the gap between them had jumped to 12.7years.

In other words, the poorest fifth of 50-year-old American mencan now expect to live just past 76, six months shy of the previousgeneration. The richest 50-year-olds should make it almost to 89,seven years longer than their parents' generation.

The study focuses on men because the researchers considered thedata on women less reliable. Women's move into the workforce overthe past 40 years can skew the numbers, for example, becauseearlier generations of women sometimes had low reported earningswhile having a relatively high socioeconomic status. While theresearchers weren't prepared to produce specific estimates forwomen, though, they were confident that women experienced a“similar if not larger change over time” compared with men,citing a previous analysis.

One important result of this 13-year life expectancy gap: SocialSecurity and other government programs, such as Medicare, arebecoming a much better deal for well-off Americans.

Three decades ago, the richest and poorest retirees couldexpect about the same amount of benefits out of governmentprograms. The richest generally got larger Social Security payouts,both by qualifying for higher checks and by living longer. Thepoorest got more out of other programs, such as Medicaid and SocialSecurity disability insurance. Medicare offered about the samebenefits to rich and poor.

The math has shifted dramatically. As wealthier people livelonger, they can expect to collect much more from Social Securityover their lifetimes than the poor. This chart shows thegrowing gap, based on the present value of benefits to a50-year-old looking ahead, and using 2009 U.S. dollars to accountfor inflation.

In 1980, a wealthier 50-year-old could expect to collect$103,000 more than a poor American. Thirty years later, the gap was$173,000. “These results suggest that Social Security is becomingsignificantly less progressive over time due to the widening gap inlife expectancy,” the researchers write.

The U.S. retirement system looks more even-handed if you includein the analysis all government benefits received and all taxes paidby Americans after age 50. Still, longer lives are giving the richand upper middle class a big financial boost, especiallythrough Medicare and Social Security, even as the poorestAmericans lose ground.

There are several theories on why the health of wide swaths ofthe U.S. is getting so much worse while the wealthy are thrivingand living so much longer. Some cite rising levelsof substance abuse, obesity, and suicide. Others point tothe ways economic inequality drive health inequality. The cost ofgood health care has skyrocketed, even for people who aretechnically covered by insurance.

Your expected life span is obviously a factor when planningand saving for retirement. The longer you live, the more valuableSocial Security is as a safety net to supplement your savings. Lifeexpectancy trends also affect the long-term finances of entitlementprograms such as Social Security.

For the moment, the most pressing question is why somany Americans are dying young, and how to stop it.

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