How to lengthen (or shorten) your life


This chart from the January issue of Scientific American provides a way of thinking about healthy and unhealthy habits.  David Spiegelhalter, a professor of risk assessment at the University of Cambridge in England, has developed a unit of risk measurement called a “microlife,” which is 30 minutes of an average person’s life expectancy.

It’s a good way to think about your habits, and to motivate yourself to adopt good habits.

Sitting on the sofa for four hours straight will subtract an hour from your expected life, but you can make that up by exercising vigorously for 20 minutes.  If you exercise for 20 minutes, you’ll add an hour to your life expectancy, according to Spiegelhalter.  But if you exercise an additional 40 minutes, you’ll gain only 30 minutes in life expectancy, which is a net loss—unless you like exercise.

Current research indicates that having a moderate alcoholic drink once a day will add 30 minutes to your expected life.  But if you take two more drinks, the gain will be canceled.   It is the fourth drink that will shorten your expected life.

Spiegelhalter very properly cautions that these are averages, and that not every individual will react in the same way.  Winston Churchill, according to a biography I’m reading, never went very long without a drink or a smoke.  I would say he was a high-functioning alcoholic.  Yet he lived to be 90.  He was in his late 60s during his first term as Prime Minister (1940-1945) and was 80 when he stepped down from his second term (1951-1955).  But that doesn’t mean that you or I could live as he did and be able to function as he did.

This is all about “chronic” risks—the things you do that affect your life expectancy in the long run.  Spiegelhalter gave an interesting TED talk on “acute” risks—the things you do that affect your odds of sudden death.

Spiegelhalter’s measurement of acute risk is the “micromort”—a chance in a million of sudden death.  As he pointed out, this is roughly equal the chance that a coin will come up “heads” in 20 flips in a row.

He pointed out that chronic risk and acute risk can’t be measured on the same scale.  That’s an important insight.  When I reported on nuclear power for the Rochester Democrat and Chronicle during the 1980s, many risk assessors failed to make that distinction.  They said the risk of living next to a nuclear power plant was less than the risk of smoking a pack of cigarettes a day.

As with his “microlive,” his “micromort” measurement is a good way to clarify the issue.  I think Spiegelhalter’s figures are good when you are comparing things of which there is a lot of experience—the risk of automobile travel, for example, versus the risk of traveling by train or airplane.   The problem with it comes when you try to assess the risk of a Black Swan event—that is, when you are trying to predict the probability of the unpredictable.

The Fukushima nuclear plant disaster is an example of what I mean.  After the event, officials said that nobody could have predicted that an earthquake and a tsunami would occur at the same time.  “Nobody could have predicted…”.  Exactly so.

Click on An Early Nuclear Warning: Was It For Naught? for more about the Fukushima disaster and risk assessment

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