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.


So, are you aware of any sub-populations in our culture made up of people over 60 who have led active lives (non-sedentary) and eaten non-processed foods continuously since childhood, that we can use as a comparison? If so, what do they die from, at what ages, and what are their lives in later years like?
It is conceivable that the rise in heart disease and cancer in the 20th century is due more to tobacco use than processed food. Serious marketing of cigarettes to women began in the late 20s and early 30s, and, if I recall correctly, statistics for heart disease and cancer deaths in US women began to spike about 40 years later. Since I suspect that the consumption of processed food is not gender specific, the fact that heart disease and cancer began to rise in men a couple of decades before it did so in women, would seem to indicate a correlation to tobacco use rather than processed food consumption.
I don't think you're using life expectancy data appropriately, there. Life expectancy at older ages will always increase by less than life expectancy at younger ages, because there are fewer opportunities to not die for older folks.

The more interesting data would be an actual percentage of population of old folks. The executive summary of the first report cited says that the percentage of folks over 75 has doubled between 1950 and 2000, and is expected to double again by 2050. (the relevant chart is p. 39, the executive summary is on p. 26, both page numbers of the pdf, not the document)

The data showing a huge increase in heart disease is not necessarily reliable, because definitions and diagnosis techniques have changed over the past 100 years. I couldn't find a good description of the methodology, and I don't really feel like looking it up at the CDC.
If a population is growing, its percentage of old people (say over 60) will fall over time. If the population is shrinking, the percentage will consistently rise over time. (caveat--this is in the long term, neglecting any temporary spikes or valleys in birth rate) The only time the percentage can remain constant is when the birth rate equals the death rate.

That addresses the final point in your line of argument, but the real problem is that you're looking at the wrong data. You need to research historical cancer rates as a function of age: that will tell you if recent lifestyle changes have impacted cancer/heart disease rates. Making multi-step inferences from large pools of tangentially related statistical data is always a tricky proposition.
Re:age adjusted death rates

In 1999, Morbidity and Mortality Weekly reported on the history of health and tobacco use in the 20th century. (The page is available online at

Illustrating the effect of anti-smoking efforts begun in the wake of the first Surgeon General's report in 1964, the article states:

"With the subsequent decline in smoking, the incidence of smoking-related cancers (including cancers of the lung, oral cavity, and pharynx) have also declined (with the exception of lung cancer among women). In addition, age-adjusted death rates per 100,000 persons (standardized to the 1940 population) for heart disease (ie, coronary heart disease) have decreased from 307.4 in 1950 to 134.6 in 1996. During 1964 to 1992, approximately 1.6 million deaths caused by smoking were prevented."
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