Friday, February 17, 2006

Life Expectancy - Beyond the Statistics

Today I received a number of emails asking questions about my article yesterday, The Fat Facts - Oh How We Eat!, and pointing out that back then life expectancy in the early 20th century was just about 50 years.

Ahhh, the statistics of life expectancy!

Life expectancy is a tricky thing to get a good handle on - for example, we know that back in 1910 the average life expectancy at birth was just about 50-years. At the time, that was true - and the years expected to live was based on what the population could expect at the time. What the statistic doesn't show us though is how many people actually lived beyond that age or why.

The 1910 census tells us that there were 91.6-million people in the United States and 11.6% were age 65 or older. Yes, in 1910 that many people, born in or before 1845 managed to survive to at least age 65....they survived infectious disease, accidents, poor hygiene and the other obstacles of the day. In that year, 4% of the population was age 85 or older....these folks were born in or before 1825! The life expectancy in 1850 was just 39-years! For those who managed to live to 85-years old in 1910, they had another 4-years on average in their life expectancy - put another way, odds were good they'd live to 89.

Those actually born in 1910 actually saw little change in their life expectancy compared with those born in 1850 if they survived to age 40. Those born in 1850 who survived to 40 had a life expectancy of 69 years, those born in 1910 who reached 40 had a life expectancy of 68 years. Little changed for either population who reached 60 years old. Those born in 1850 could expect to live to 74, those born in 1910 could expect to live to 74.

So, how are we doing now? Pretty good. Someone who was 40 years old in 2003 can expect to live to 79 - ten more years than those born in 1850 or 1910. A 60 year old in 2003 can expect to live until they're 82 - twelve more years than older generations. Where things really haven't changed dramatically is in life expectancy for those who reach 70 and 80. If one was 70 in 1910, odds were good they'd live to 78....if they were 80, odds were in their favor they'd live to 85 or older. In 2003, a 70 year old had a good chance to live to 83 (five years more than in 1910) and an 80 year old had a good chance they'd live to 88 or older (three more years), those who reached 85 are expected to live until 89 (the same as 1910).

Prior to 1950, increasing life expectancy was mainly due to more children surviving childhood, a greater understanding of proper hygiene and improvements in the workplace for young adults which resulted in fewer accidental deaths. Since 1950, life expectancy increases are due to better healthcare, especially care of adults who reach 40 years or older - basically medical screening and treatment is undeniably better now than it was 60 years ago - and there is a much broader access to healthcare across the population. The greatest advance in longevity is really in those who reach age 60...but this longer life expectancy trend levels off pretty much the same once one lives to 80 as it has in the past.

I'm not trying to confuse here - it's just that when you hear that in 1910 people lived an average of 50 years and today we live an average of 80, it sounds like we're living much much longer. What we're doing better, in reality, is keeping our kids alive in childhood and giving them better odds of hitting 40. If they reach 40, they do have a distinct advantage over those born in previous generations due in part to greater access to healthcare....but by the time they're 70 that starts to level off and by 80 there really isn't all that much difference in life expectancy between someone who was 80 in 1910 compared with someone who was 80 in 2003, someone with radically improved medical technology and access to care - remember, back in 1910, few seniors had health insurance!

In our determination to unlock the secrets of longer life, let's not forget how important quality of life must be - if we're going to live longer, shouldn't we try to live in good health too? We've done a fantastic job improving the lives of our children (and the survival of women in childbirth) along with tackling many things considered "background" causes of mortality (violence, accident and some infectious disease)...we still need improvement in what's called "senescent" causes of mortality - diseases and conditions that impact our health that rise sharply as we age, like cardiovascular disease and cancer. Between 1850 and 2000 we'd increased life expectancy at birth from 40.9-years to 80.8-years....between 1850 and 2000, the change in "senescent" life expectancy only increased from 72.6-years to 81.9-years. Since 1979 we've improved life expectancy for those who reach 60 years of age by just over one year, from 78.3 in 1979 to ....79.8 in 2003. Sadly, at the same time, years in "ill-health" has increased too, from six years in 1979, to more than nine, with women in 2003 averaging 10.7 years in ill-health and men averaging 8 years in ill-health. We're living longer, but we're not living as well when it comes to our quality of health declines in our later years.

And let's not forget something that is more telling - humans actually have the potential to have a maximum lifespan of about 125 years. Robert Mitchell, professor of biology at Penn State has said, "We have to distinguish between maximum lifespan, which is as long as any human has ever lived, and life expectancy, which is how long you could live predictably, based on insurance statistics, for example. As far as maximum lifespan goes, we suspect it's around 125 years. There is no evidence that humans can live any longer than that."

History provides us with insight into a number of people who've lived past 100-years. The longest lived human (verifiable) was a French woman - Jeanne Calmet - died in 1997 at the age of 122, and she even smoked until she was 119 and finally gave up the habit when she grew tired of asking others to light her cigarrettes for her due to her declining eyesight.

If we have the potential to live to be 125 - in decent health - why are we not seeing rapid improvements in our average life span to reach our potential? In years gone by it was a matter of living through childhood, infectious diseases and avoiding accidents that mattered - if you could make it to 40 you'd probably make it to if you make it to 40, even with all of our advancements, you'll only likely make it to 80 - an increase of just ten years over what's almost a century of progress.

Most promising today is research that is investigating the aging process of humans and other animals - specifically how well our body system repairs damage. The better we can repair cellular damage, from things like oxidative stress, the longer we live.

Research published in 1998, in the Journal of Comparitive Physiology - The rate of free radical production as a determinant of the rate of aging: evidence from the comparative approach - found that "Available research indicates there are at least two main characteristics of longevous species: a high rate of DNA repair together with a low rate of free radical production near DNA."

What causes the damage and stimulates the repair cycle?

Well, for that, you'll have to do some reading:

Damage-Based Theories of Aging


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