​The Healthy Survivor Effect

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Saturday, July 21, 2012 12:27 pm Email this article

You are constantly seeing articles about studies showing that if you do X, then Y happens. Last week the Press made too much of an epidemiologic study in BMJ Open "showing" that...

1. Cutting TV viewing to less than 2 hours per day extends life by 1.4 years.
2. Sitting 3 hours less each day adds 2 years to lifespan.

It may be true or it may not, but the study did not SHOW it. Epidemiological or population studies cannot prove such a thing; only prospective randomized controlled trials can. Read my book Medical Myths Doctors Believe, available on amazon.com or Kindle, to learn the difference.

Look. Who is more likely to spend extra time watching TV? Who spends more time sitting? Many possible answers here, but one likely answer is sick people; and sick people tend to have a shorter lifespan, not because they sit, but because they are sick. Vigorous healthy people are more likely to exercise and go outdoors; they tend to live longer, not because they go outdoors but because they were healthier to begin with. So you cannot conclude that inactivity shortens lifespan. Suppose I tell you that the people who climbed Mt. Hood were more likely to live longer than the average American? Would you conclude that climbing Mt. Hood makes people live longer? No because you know that the climbers were more fit to begin with; otherwise they could not have completed the climb. The Press loves, I mean really l-o-v-e-s epidemiological studies, but only if they confirm widely-held beliefs. But YOU should not do dangerous things or overstretch your limits because of epidemiologic studies. Wait for the hard science to arrive, the prospective study. It may never come. And if it does come, the Press may not print it unless the conclusion supports what they already believe. This is a faith-based nation. But I am and YOU should be a science-based person. After all, in the end, reality matters.

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