nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
See here for more discussion.

Monday, March 21, 2011

Comparing Health Risks Requires Understanding Of Biology

This is a Food-For-Thought post about judging potentially harmful health effects.

Suppose I tell you that exposure to something carries a negligible risk of serious harm, one in a million, say.  Now I tell you that 100 million people are going to be exposed to that risk.  Does it make a difference to our perception of risk--that is, do we take action to prevent it--because now there are, on average, 100 people in that 100 million who will experience that harm?

If you look at the question from the point of view of yourself, as an individual, and realize that there are thousands of things you are routinely exposed to every day with orders of magnitude greater risk (1 in 100,00 for instance...which is close to the risk of a dying in a car accident), the risk is non-existent because it's so yourself...and in the larger scheme of total risk.

If you look at the big picture of those 100 in the total of 100 million and think, "This is a measurable level of risk to individuals that is morally wrong to tolerate,"  and assuming that something can be done to remediate it, you would want to eliminate the risk.

What makes one person see a given risk as not worth considering, and another person as a risk to correct?

Before concluding that this is an unrealistic hypothetical, consider that the body scanner at the airport delivers a very small dose of ionizing radiation.  The measure used is "sieverts" (the parallel of "meters" for length and "grams" for weight).  Radiation exposure is a lifelong cumulative risk; a single exposure isn't a causative event, it's the total amount you recieve over a lifetime that increases the risk.  You receive about 0.0001 millisieverts from a body scanner (one ten-thousandth of a millisievert)

--You receive about the same dose from flying at 30,000 feet in an airplane for two minutes.

--You receive about 2.4 millisieverts a year, just from living on the planet due to bombardment of the earth with radiation...called background radiation.  This can vary from 1 to 10 millisieverts a year depending on where you live.  Background radiation alone will cause 1 in 100 to dies of cancer (the cumulative effect of going to the beach, flying, and just being on the earth) according to one expert.  See here for a discussion.

--You receive about 10 millisieverts from a CT scan to detect cancer.

--People living in Tokyo are being exposed to 0.001 millisieverts.  That's one-thousandth of a millisievert, again, for clarity).  Note that this is 150 miles away from the affected reactors.

Now, back to my hypothetical.  The risk of cancer from an airport body scanner is about 1 in 80 million...even lower than my example of 100 in 100 million.  Given the magnitude of routine exposures above, and the cumulative nature of radiation exposure risk, does an airport scan worry you?

Yep, it adds a miniscule amount to the lifetime total.  But you could get body scanned a hundred times and not reach the dose obtained by a day at the beach.  A CT scan is the equivalent of four days living on the earth.

[By the way, there are alternative airport scanners that use millimeter wave scanners--using radio waves--to scan the body instead of ionizing radiation.  The two types of scanners cost about the same]

To carry this further, are you worried about radiation from Japan?  By the way, the half-life of radioactive iodine is about eight days.  Most of what leaked from the core container has already decayed.

My theory is that so few people understand the biology of how radiation affects our bodies that it becomes a boogey man, something to panic over.  The less we understand, the greater our belief that it's deadly.  The philosopher Montaigne once said,
"Nothing is so firmly believed as that about which we know the least."
Radiation is a real hazard, but only if you're standing near the leaking core container in Japan.  Conflating that hazard with radiation hazard from medical treatments and airport scanners is comparing (in size) a grain of sand to Mt Everest.

Doc D

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