Wednesday, June 11, 2008

Too young to die of cancer

Unless the rate of lung cancer deaths has changed dramatically in each age group, since 1902, lung cancer would not have been that great a threat at the turn of the last century, simply because the vast majority of people were dying at a much earlier age. Comparing overall lung cancer rates (across all age groups in the population) for different time periods since the turn of the century would distort the data as life expectancy increased and the number of people in each age group changed.

The probability of developing, and dying from, lung cancer during one’s lifetime would increase simply because the average lifetime had increased. Have epidemiologists been comparing apples and oranges?

Recently, I came across an article, or at least part of an article, I’d saved several months back. Unfortunately, at that time I was not seriously considering writing a blog and had already started the bad habit of failing to note the source of the information. I had also neglected to make any notes on why I was saving that particular piece of trivia.

The article noted that, in Canada today, most people die in old age. In 2002, for example, almost 80% of people who died in Canada were 65 years of age or older.

In 1926, which was the first year vital statistics were compiled for all provinces, only one in six deaths (roughly 17%) occurred in the population 65 or older. Those same statistics show that 30% of deaths occurred in children under the age of five.

At first glance, there doesn’t appear to be much significance to those statistics. It’s fairly common knowledge that in 1926, people died at a much younger age than they do today.

Advancements in medical science have wiped out or controlled childhood disease to the point where, in 2002, less than one per cent of deaths occurred prior to the age of five. This has, in turn, led to a significant increase in life expectancy, currently around 80, with women living slightly longer than men. It also means that, thanks to the advances in medical science, a much greater portion of the population is living to 65 and beyond.

But what does all this have to do with smoking?

In my last post, I noted that, according to figures obtained from StatsCan, 71.7% of all cancer deaths (malignant neoplasm), and 70% of lung cancer deaths, occurred after the age of 65. This suggested to me that cancer, in all its forms, was a disease associated with age. I also drew a nice little chart based on the figures from statistics Canada.

I read a blog by Dr. Michael Siegel, The Rest of the Story, on a regular basis. A comment made by one of his readers asked, since people have been smoking for hundreds of years, why was the lung cancer epidemic not apparent until the 1930’s.

Many in the anti-smoker cartel point to the introduction of machine made cigarettes at the turn of the century, and the resulting increase in smoking prevalence, and attribute the increase in lung cancer deaths to smoking tobacco. Some say that the prevalence of other lung diseases meant many cancers were simply misdiagnosed, based on medical knowledge, or the lack thereof, at the time.

But, there may be another explanation for the alleged cancer explosion in the thirties.

Although I couldn’t find a Canadian statistic, a US chart shows average life expectancy at birth in 1902 as 50.7 and by 1933, it had increased to 57.7. It has been increasing steadily since then and by 2002, average life expectancy in Canada was just under 80.

If, in 1926, 83% of deaths occurred before the age of 65, is it possible that people simply weren’t living long enough for cancer, including lung cancer, to develop? Is it possible that the increase in lung cancer mortality rates is due to a statistical anomaly revealed by the rapid increase in life expectancy during the first half of the past century?

Was cancer, including lung cancer, simply waiting for average life expectancy to catch up to and/or exceed the incubation period.

As I’ve mentioned before, I’m neither an epidemiologist nor a statistician. But I am curious.

If anyone reading this post knows of a study which shows how (if?) the increase in longevity, and the redistribution of age groups within the population, was taken into consideration when categorizing smoking as the sole culprit in lung cancer deaths, please leave a comment with the appropriate link.

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