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Tuesday, August 09, 2005
We have more old people, but not more really old people
When I complain that Americans' fattening diets and sedentary lifestyles are giving us cancer and heart disease, I'm often countered, even by incredibly knowledgable and intelligent people like my mother, that people get these ailments more often these days because people are simply living longer, and thus have a larger window of opportunity to become sick. My intuition of course told me that eating more processed foods and sitting at desks all day makes people unhealthy is quantifiable ways, manifested in, for example, cardiovascular disease rates over time.
So today I actually bothered to do some research on life expectancy and age distribution in the United States in the past century, and naturally I found what I was looking for. Thanks, Google.
This chart contains fascinating data (page 77 of the document, in case the permalink isn't working). Indeed, the US life expectancy at birth has shot up consistently since the McKinley administration. In one century, the aveage lifespan of Americans doubled, from 47.3 years in 1900 to 77.0 in 2000. No surprise there. Simple medicine - antibiotics, fewer deaths during childbirth, less life-threatening disease among children - makes people live longer.
But look down at the life expectancy after the age of 65, and then after the age of 75. From 1950 to 2002, the life expectancy at birth picked up nearly 10 years. In that same timespan, the life expectancy if you made it past 65 went up less than 5 years.
From 1980 to 2002, life expectancy at birth increased 3.6 years; after 65 years old that number is 1.8; and after 75 years old that number drops to 1.1 years.
The point of all this is that as time progresses and technology does too, the medical community is most talented at lowering mortality rates among pre-retirees. There have always been individuals in populations who live to be really old, and everyone past a certain very old age ends up living to about the same age, no matter how spectacular medicine is in their generation. (Hell, Plato lived to be 80; Archimedes croaked at 75.) The top end isn't going up that much over time.
This is relevant to the disease/age argument because most cases of those persistently deadly afflictions like cancer and heart disease occur after the age of 60. Check out page 14 of this report, or page 16 of this one. Cancer and heart disease rates take a massive jump at 60 and 50 years old.
Given that the percentage of the population over the age of 60 remains fairly consistent over the decades, any increase in these diseases among the entire American population is attributable only to environmental factors, and not the fact that there are more old people hanging around. Of course the aging Baby Boomers throw a wrench in this model.
But that blip is not applicable to the mind-blowingly massive increase in heart disease over the last century. Look at the first graph on page 8 of this report. Heart disease deaths go from almost zero in 1900 to roughly the current rate in about 1970, back when Baby Boomers were still hip grad students, but long after processed foods had invaded our diets.
I've never taken a course in statistics, so undoubtedly my analysis of these data contains some errors, but I think at the very least people who claim that more old people are suddenly cropping up in our population should re-examine the evidence.
That's right, Beetle, I'm talking to you.
posted by Rebecca C. Brown at 9:27 AM
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