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Author Topic: Radiation hormesis?  (Read 10535 times)
paddyfool
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« on: July 01, 2012, 05:15:36 am »

Pretty out there, so far as theories go.  And is anyone seriously suggesting a benefit to annual doses of 300 mSv? (100 times earth normal).

Also, I'd recommend this article as a summary of some of the best available study data, although it's a bit old: http://bjr.birjournals.org/content/76/901/1.full

Put simply: Before 1960, when radiologists were exposed to relatively high doses of occupational radiation (>5 mSv), they died earlier than other doctors on account of increased cancer mortality.  After that, not so much, and the data for British physicians at least seems to show a decreased rate of death from non-cancer mortality among radiologists more recently.  However, it seems unlikely that this would be down to radiation exposure, as you're talking about exposures to pretty tiny levels of radiation (<1 mSv), and there may well be differences in lifestyle between radiologists and other doctors.
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SandySandfort
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« Reply #1 on: July 01, 2012, 06:39:02 am »

Pretty out there, so far as theories go.  And is anyone seriously suggesting a benefit to annual doses of 300 mSv? (100 times earth normal).

No study has ever been conducted that showed that low levels of radiation are dangerous. None. All the dire warnings are derived from the  assumption that radiation's biological damage is linear.

However, numerous studies have shown that low levels of radiation reduce the incidence of cancer and other illnesses. In fact, it would appear that most people are gamma deficient.

Mellyrn may jump in  on this, or you can google radiation hormesis.
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Tucci78
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« Reply #2 on: July 01, 2012, 07:31:03 am »

Before 1960, when radiologists were exposed to relatively high doses of occupational radiation (>5 mSv), they died earlier than other doctors on account of increased cancer mortality.  After that, not so much, and the data for British physicians at least seems to show a decreased rate of death from non-cancer mortality among radiologists more recently.  However, it seems unlikely that this would be down to radiation exposure, as you're talking about exposures to pretty tiny levels of radiation (<1 mSv), and there may well be differences in lifestyle between radiologists and other doctors.

Having known radiologists both personally and professionally for decades, I always figured that their higher death rates were due to the fact that most of 'em smoked like chimneys. 

Until the "Smoke-Free Hospital" doctrine took hold, I'd never once entered a Radiology Department's reading rooms without encountering the stench of tobacco smoke and the sight of overflowing ashtrays, many of them improvised from hospital cafeteria crockery. 

Hey, you spend most of your life in darkened little subterranean chambers getting pestered by people like me wanting to know whether those stat studies from the Emergency Department show anything significant. 

I consider it something of a miracle that the only stuff they were smoking was tobacco.

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paddyfool
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« Reply #3 on: July 01, 2012, 08:53:12 am »

Pretty out there, so far as theories go.  And is anyone seriously suggesting a benefit to annual doses of 300 mSv? (100 times earth normal).

No study has ever been conducted that showed that low levels of radiation are dangerous. None. All the dire warnings are derived from the  assumption that radiation's biological damage is linear.

However, numerous studies have shown that low levels of radiation reduce the incidence of cancer and other illnesses. In fact, it would appear that most people are gamma deficient.

Mellyrn may jump in  on this, or you can google radiation hormesis.

I didn't just leap into this without doing some Pubmed reading first.  But the key to what the advocates of radiation hormesis are talking about lies in the findings from really low doses of radiation, and specifically from cancer excess not being seen at levels <100 mSv.  On the contrary, there's good evidence that doses about 100 mSv (never mind 300 mSv, or "a hundred times Terra background") genuinely are harmful; it's below this level that things get ambivalent.  

See this article for more: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/?tool=pubmed
« Last Edit: July 01, 2012, 09:07:30 am by paddyfool » Logged
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« Reply #4 on: July 01, 2012, 05:53:20 pm »


No study has ever been conducted that showed that low levels of radiation are dangerous. None. All the dire warnings are derived from the  assumption that radiation's biological damage is linear.

However, numerous studies have shown that low levels of radiation reduce the incidence of cancer and other illnesses. In fact, it would appear that most people are gamma deficient.

When my dentist got a new digital xray sensor, one of the touted benefits was a much lower xray dose for the same picture quality.  When I read up on it, however, I discovered that radiation levels substantially *lower* than earth background have been shown to be harmful.  It seems that the really low levels do so little damage, it fails to trigger DNA repair mechanisms - like the old malicious viruses that would flip one random bit somewhere on your harddrive every hour or so.  You would not notice anything wrong until much too late... 

The digital xray dose was low enough, that there was some concern it might be hitting that leg of the curve.  Fortunately, it is an easy problem to fix once there is enough hard data to quantify the optimum dose.  :-)
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sam
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« Reply #5 on: July 01, 2012, 06:29:23 pm »

Pretty out there, so far as theories go.  And is anyone seriously suggesting a benefit to annual doses of 300 mSv? (100 times earth normal).

The fallout from Chernobyl was extremely patchy.  So if Chernobyl level fallout caused harm, we would expect some cancer clusters highly localized in the high radiation patches.

Allegedly there is thyroid cancer cluster, which has killed a grand total of nine, yes nine, people.

However, it is plausible that this is an artifact of increased diagnosis, rather than increased cancer - lots of people die of old age with lumps in their thyroid that cannot be distinguished from cancer, other than that nothing much happened in consequence.

If Chernobyl killed millions, or thousands, or hundreds, the patchiness of the fallout should have caused patchiness in the deaths, which should result in detectable clusters.

There are no detectable Chernobyle clusters, with the arguable exception of the thyroid cluster.
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sam
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« Reply #6 on: July 01, 2012, 06:36:49 pm »

I didn't just leap into this without doing some Pubmed reading first.  But the key to what the advocates of radiation hormesis are talking about lies in the findings from really low doses of radiation, and specifically from cancer excess not being seen at levels <100 mSv.  On the contrary, there's good evidence that doses about 100 mSv (never mind 300 mSv, or "a hundred times Terra background") genuinely are harmful; it's below this level that things get ambivalent.  

See this article for more: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/?tool=pubmed

Which article tells us:
Quote
Contrary to previous claims, there was no increase in leukemia or other cancers (except thyroid cancer) in regions contaminated after the Chernobyl accident where thyroid doses ranged up to 1 Sv (123). The increase in thyroid cancer among young children is correlated with dose (124), and a threshold at 200 mSv is compatible with data (125).

The evidence for an increase in thyroid cancer is equivocal, because with thyroid cancer, the more you test, the more "cancers" you find.  There is no evidence of an increase in deaths from thyroid cancer.

So all up, Chernobyl event indicates that with the possible exception of thyroid cancer, there is no low dose effect below 1Sv (1000 mSv)

Chernobyl was the largest natural experiment in low dose radiation effects, randomly plonking patches of radioactivity all over the place according to the accidents of wind and weather.
« Last Edit: July 01, 2012, 07:04:45 pm by sam » Logged
Helian
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« Reply #7 on: July 01, 2012, 09:24:31 pm »

Why does everyone seem to think cancer will be an issue in the future?  I they've already cured it.  I hope they're up to primates, but I know I've heard of lab rats being cured.

This one is from 6 months ago, only did a quick search on kanzius machine.
http://www.theblaze.com/stories/could-an-idea-started-with-pie-tins-and-hotdogs-lead-to-symptom-free-cancer-treatment/

Basically they extract some cancer cells, make a gold fleck (nanite) that self attaches to that type of cancer, and inject the nanites into a patient.  After enough time for it to spread through the whole blood stream/body they zap the patient with radio waves, frying whatever the nanites were attached to.  The way it attaches to the cancer cells is related to how the cancer grows & spreads, so it gets all of it regardless of what organ it is in, stage 4 shouldn't matter.  Surrounding tissue is completely unharmed, no side effects.  That article states up to 3 years till human trials, so 2.5 from now.  Millions of dollars and outsourcing are being used to speed up the process.

The argument for AnCap, or at least WAYYYY less government intervention, how many will die while this goes through FDA approval.
P.S. I hear the Israelis came up with a very promising cancer vaccine.
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paddyfool
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« Reply #8 on: July 02, 2012, 06:36:08 am »

Why does everyone seem to think cancer will be an issue in the future?  I they've already cured it.  I hope they're up to primates, but I know I've heard of lab rats being cured.

Two problems with this:
- One is that the number of things which show promising results in lab rats is much larger than the number of things which actually work when tested in humans.  So take everything you hear about revolutionary results from something tried in animal testing with a very large pinch of salt - any such finding is still in the very early stages.
- The other is that cancer is not a disease, but a category of diseases.  It's basically what happens when the regenerative capacity of your body goes wrong, and things start growing where they shouldn't, or not dying where they should.  The characteristics of different cancers and their appropriate treatment vary massively by the organ of origin and on exactly how the cancer cells have turned cancerous.  I very much doubt there will ever be any single cure for cancer, any more than there will ever be any single cure for "infection".

Also, people think that cancer will be a leading cause of death in the future because it's a straightforward extrapolation both from the past century or so, and from current demographic trends.  Currently, cancer is the second leading cause of death in the USA today, and on course to overtake the leading cause (heart disease), although back in 1900 it was back in 8th place (largely because most people died of something else first): http://www.nejm.org/doi/full/10.1056/NEJMp1113569.  The risk of getting most cancers, meanwhile, strongly increases with age; so as the population gets older, we're going to see more and more cancer.


Which article tells us:
Quote
Contrary to previous claims, there was no increase in leukemia or other cancers (except thyroid cancer) in regions contaminated after the Chernobyl accident where thyroid doses ranged up to 1 Sv (123). The increase in thyroid cancer among young children is correlated with dose (124), and a threshold at 200 mSv is compatible with data (125).

The evidence for an increase in thyroid cancer is equivocal, because with thyroid cancer, the more you test, the more "cancers" you find.  There is no evidence of an increase in deaths from thyroid cancer.

So all up, Chernobyl event indicates that with the possible exception of thyroid cancer, there is no low dose effect below 1Sv (1000 mSv)

Chernobyl was the largest natural experiment in low dose radiation effects, randomly plonking patches of radioactivity all over the place according to the accidents of wind and weather.

The problem here is that you're selectively quoting from an article advocating for a threshold relationship for the little bit of the data it provides which vaguely supports a higher (safe or beneficial) threshold than the authors of the article itself propose (they sum up all the data they consider by saying: "there is no convincing evidence of a carcinogenic effect in humans or experimental animals for doses of less than 100 mGy of low linear energy transfer radiation". 

Also, this particular evidence offers only vague support, partly because you can't prove a negative, and partly because there might well be vested influences in downplaying the impact of Chernobyl.

I should, at this point, however, admit to being less than complete in my linking to the evidence myself, in only linking to the article positing this alternative point of view, and not its twin article, which puts the case instead for the linear risk model. This article presents the evidence for that point of view here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663578/

To sum up, then: the jury's out on whether there's a higher safe threshold around 100 mSv, never mind any hormetic (better than safe) effects.  Partly because whatever effects there are below 100 mSv in either direction look to be really very small, and small effects (harmful or beneficial) are hard to measure.  And while it's interesting to posit that solid evidence of some small net benefit of low dose radiation might yet be found, >300 mSv is not low dose.
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sam
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« Reply #9 on: July 02, 2012, 07:12:49 pm »

The problem here is that you're selectively quoting from an article advocating for a threshold relationship for the little bit of the data it provides which vaguely supports a higher (safe or beneficial) threshold than the authors of the article itself propose (they sum up all the data they consider by saying: "there is no convincing evidence of a carcinogenic effect in humans or experimental animals for doses of less than 100 mGy of low linear energy transfer radiation".  

The only evidence they have for harmful effects at doses of less than 200 mSv is the Chernobyl thyroid cancer clusters - which evidence is unconvincing, because the cluster of thyroid cancers may well reflect a cluster of testing for thyroid cancer.  We don't have a persuasive cluster of Chernobyl related deaths from thyroid cancer.

there might well be vested influences in downplaying the impact of Chernobyl.

Oh come on.  Compare the big drama about anthropogenic global warming and chernobyl and all the rest, with any actually observed effects.  It is pretty obvious which side the vested interests on.

Ask any random person in the street, chances are he thinks that Chernobyl killed a billion people and polar bears are dying of heatstroke.  Al Gore has made billions out of the Anthropogenic Global Warming scare, selling carbon indulgences, which pay for his private jet, and his gigantic mansion, with all the lights and air conditioning he leaves on all night.

Ask any random person in the street about species extinction, and he will tell you that every year ten thousand species go extinct, or ten million species go extinct, despite the fact that no one can name any species that have gone extinct in the last year or two.  People make billions out of supposed endangered species, by threatening to take away people's land.  "Pay me ten thousand dollars in consultation fees, or I will discover that your land is vital to endangered species."

Come to think of it, my land actually is vital to supposedly endangered species, since supposedly endangered species steal my bananas and smash my fences - though I rather think that if they were actually endangered, I would not have to watch my bananas so closely.

Radioactivity is like witchcraft.  The same vested interests that promoted belief in witchcraft, promote belief in radioactivity, for much the same reasons.

its twin article, which puts the case instead for the linear risk model. This article presents the evidence for that point of view here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663578/

Anyone claiming linear is refuted by Chernobyl, an unintended experiment carried out on a gigantic scale.  If the effect was linear, then we would see enormous patches of excess deaths, because Chernobyl fallout was patchy.

We only see excess deaths in regions exposed to significantly more than 1000 mSv.  Either people are dying like flies, or the most careful examination only finds questionable effects at the very edge of statistical significance, with nothing in between.  It is an obvious threshold effect, with the threshold setting in somewhere around 1000 mSv or so, with the possible exception of thyroid cancer, which, if it is an exception, killed around nine people.
« Last Edit: July 02, 2012, 08:03:26 pm by sam » Logged
Andreas
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« Reply #10 on: July 03, 2012, 02:43:59 pm »

Radiation is one thing.
But it has to come from somewhere. Some isotopes are such that I would strongly advise against tolerating their presence, even if the radiation output is low.
Radioactive isotopes of cesium for instance, have the unfortunate property, that the sodium pump can mistake them for Potassium, pumping them into the cells of the body... but the cell membrane port that lets potassium back out aren't so easily fooled. This means that radioactive cesium has a much higher probability of degrading (and producing radiation) close to the nucleus of biological cells.
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paddyfool
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« Reply #11 on: July 04, 2012, 07:09:32 am »

Oh come on.  Compare the big drama about anthropogenic global warming and chernobyl and all the rest, with any actually observed effects.  It is pretty obvious which side the vested interests on.

Let's leave AGW (and species extinction) out of this.  With Chernobyl, certainly, environmentalists might overhype it, but those responsible also have a major incentive for a cover-up.

More relevantly, though, to the doses in question, you're talking small effects and limited scope to observe them without close observation.  Which there seems to have been to a better extent with the Japanese Survivor Survey (from those exposed to another very large natural experiment, which is what the linear model is based on).

Quote
Anyone claiming linear is refuted by Chernobyl, an unintended experiment carried out on a gigantic scale.  If the effect was linear, then we would see enormous patches of excess deaths, because Chernobyl fallout was patchy.

We only see excess deaths in regions exposed to significantly more than 1000 mSv.  Either people are dying like flies, or the most careful examination only finds questionable effects at the very edge of statistical significance, with nothing in between.  It is an obvious threshold effect, with the threshold setting in somewhere around 1000 mSv or so, with the possible exception of thyroid cancer, which, if it is an exception, killed around nine people.

Do you have a source on that 1000 mSv figure?  It would seem to contradict this data (where they saw a significant increase in leukaemia among those with 150-300 mSv of exposure) http://www.bmj.com/rapid-response/2011/10/29/elevated-leukemia-rates-chernobyl-accident-liquidators
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sam
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« Reply #12 on: July 04, 2012, 06:12:03 pm »

Oh come on.  Compare the big drama about anthropogenic global warming and chernobyl and all the rest, with any actually observed effects.  It is pretty obvious which side the vested interests on.

Let's leave AGW (and species extinction) out of this.  With Chernobyl, certainly, environmentalists might overhype it, but those responsible also have a major incentive for a cover-up.

Those responsible are the government of the Soviet Union, which no longer exists.  Most of their successors seem perfectly happy to blame anything and everything on them.

Further, the successor regime is still hyping the bejesus out of Chernobyl, rather than covering up.  People are still forbidden to go into areas that once upon a time used to be radioactive, even though there is no evidence that people suffered detectable harm even back when they actually were radioactive.

More relevantly, though, to the doses in question, you're talking small effects and limited scope to observe them without close observation.

That is a criticism of all studies before Chernobyl.  Chernobyl was an experiment on a gigantic scale.  If there were low dose effects, they would show up.

If low dose effects, should have killed about four thousand people, a large proportion of them in a few small towns near Chernobyl.  That would be statistically detectable.

The Chernobyl results are:  No indication of a low dose effect below 200 mSv.  Questionable evidence of a low dose effect for thyroid cancer from 200 mSv up - which thyroid cancer cluster, supposing it to be real rather than a result of over diagnosis, killed nine people.

Above 1000 mSv, people start dying all over the place.  There is no doubt whatever that 1000 mSv or more is really seriously bad for you.   If the effect was linear between 200 mSv and 1000 msV, we would see plenty of excess deaths in the 200 mSv - 1000 mSv range, which is roughly what most of the evacuees got.  We don't.

Which there seems to have been to a better extent with the Japanese Survivor Survey (from those exposed to another very large natural experiment, which is what the linear model is based on).

But the Japanese survivor survey does not support the linear model:  From the survivor survey, looks like radiation protects against cancer and improves general health in doses of 50 - 100 mSv, begins to have harmful effects on one's chances of cancer at around 100 - 200 mSv, and increases linearly thereafter.  It supports the linear model above 100 mSv, with a threshold around 100 mSv.

However, in the Japanese survivor survey, radiation shows no linear effect on total deaths, with an increase of total deaths setting in at about 1000 mSv, consistent with the conjecture that doses of radiation above 100 mSv result in a small increased risk of being diagnosed with cancer and having one's death blamed on cancer, and a decreased risk of having one's death blamed on something else.

Quote
Anyone claiming linear is refuted by Chernobyl, an unintended experiment carried out on a gigantic scale.  If the effect was linear, then we would see enormous patches of excess deaths

It would seem to contradict this data (where they saw a significant increase in leukaemia among those with 150-300 mSv of exposure) http://www.bmj.com/rapid-response/2011/10/29/elevated-leukemia-rates-chernobyl-accident-liquidators

There is no liquidator subpopulation that is known to have been exposed to only 150-300 mSv.  The radiation exposure was guesswork.  Radiation exposure of liquidators is uncertain and unreliable.

The liquidator study gives "bordering level of significance" - in other words not really significant.  Further, the significance assumes that "dose reconstruction" is precise, but the dose reconstruction was guesswork, and guesswork made by people who knew the outcome.  If someone is suffering from leukemia, people will be more apt to recall higher dose events, and more apt to interpret events as high dose events.  If someone is in fine health, people will be less apt to recall higher dose events, and less apt to interpret events as high dose.  Even assuming no such bias, some those estimated as being exposed to x amount of radiation, will in fact have been exposed to 10x amount radiation, and others to 0.1x amount of radiation, smearing out any threshold effect. 

If indeed those estimated as having 150-300mSv have higher rates of leukemia (and the result was not statistically significant) it may well be because some of those estimated as 300 mSv in fact had 1000 mSv.

Comparing studies that give different results, we see a consistent pattern:  The better the data, the higher the threshold, and the threshold is at least 100 mSv, and quite likely 1000 mSv
« Last Edit: July 04, 2012, 06:43:45 pm by sam » Logged
Oneil
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« Reply #13 on: July 05, 2012, 12:43:29 am »

I don't know the facts about routine general medical and dental X-ray's.  Yet I still can't help but cringe when I see children in particular with a cellular phone smashed against their skull. Or using notebooks with high power wireless in their laps.   Why not just have them stand in front of a worn out microwave oven?  Roll Eyes
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paddyfool
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« Reply #14 on: July 05, 2012, 03:48:33 am »

More relevantly, though, to the doses in question, you're talking small effects and limited scope to observe them without close observation.

That is a criticism of all studies before Chernobyl.  Chernobyl was an experiment on a gigantic scale.  If there were low dose effects, they would show up.

If low dose effects, should have killed about four thousand people, a large proportion of them in a few small towns near Chernobyl.  That would be statistically detectable.
[/quote]

What are you basing this statistic on?

Quote
The Chernobyl results are:  No indication of a low dose effect below 200 mSv.  Questionable evidence of a low dose effect for thyroid cancer from 200 mSv up - which thyroid cancer cluster, supposing it to be real rather than a result of over diagnosis, killed nine people.

Where are you getting these stats from?  And fine, the cluster didn't kill that many people, because thyroid cancer doesn't generally kill that many people, but you're still talking a cluster of 5,000 cases of thyroid cancer.  Some of which may have been overdiagnosis, but a lot of which may well have been the simple fact that Chernobyl released radioactive iodine, and iodine is straightaway taken up by the thyroid (which is why giving radioactive iodine is one option for killing off hyperactive thyroid glands).

Quote
Above 1000 mSv, people start dying all over the place.  There is no doubt whatever that 1000 mSv or more is really seriously bad for you.   If the effect was linear between 200 mSv and 1000 msV, we would see plenty of excess deaths in the 200 mSv - 1000 mSv range, which is roughly what most of the evacuees got.  We don't.

The figures you're giving for what the populations affected by Chernobyl got are all significantly larger than anything I'm seeing when I look this up (e.g. here http://www.who.int/ionizing_radiation/chernobyl/backgrounder/en/index.html).  Where are you getting them from?

Quote
Which there seems to have been to a better extent with the Japanese Survivor Survey (from those exposed to another very large natural experiment, which is what the linear model is based on).

But the Japanese survivor survey does not support the linear model:  From the survivor survey, looks like radiation protects against cancer and improves general health in doses of 50 - 100 mSv, begins to have harmful effects on one's chances of cancer at around 100 - 200 mSv, and increases linearly thereafter.  It supports the linear model above 100 mSv, with a threshold around 100 mSv.

However, in the Japanese survivor survey, radiation shows no linear effect on total deaths, with an increase of total deaths setting in at about 1000 mSv, consistent with the conjecture that doses of radiation above 100 mSv result in a small increased risk of being diagnosed with cancer and having one's death blamed on cancer, and a decreased risk of having one's death blamed on something else.

Source, please.  What you're saying would seem to contradict the paper I linked to before on this data.

Quote
Quote
Anyone claiming linear is refuted by Chernobyl, an unintended experiment carried out on a gigantic scale.  If the effect was linear, then we would see enormous patches of excess deaths

It would seem to contradict this data (where they saw a significant increase in leukaemia among those with 150-300 mSv of exposure) http://www.bmj.com/rapid-response/2011/10/29/elevated-leukemia-rates-chernobyl-accident-liquidators

There is no liquidator subpopulation that is known to have been exposed to only 150-300 mSv.  The radiation exposure was guesswork.  Radiation exposure of liquidators is uncertain and unreliable.

OK, so you're challenging this dose estimate.  What's your evidence that it was higher than that estimated by the study in question?

Quote
The liquidator study gives "bordering level of significance" - in other words not really significant.

No, the results weren't merely borderline. From the study results: "Both the external (SIR=2.5, P<0.001) and internal comparisons (RR=2.2, P=0.03) indicate significantly elevated risks in the 150-300 mGy dose group."

p<0.001 is a very strong level of evidence - not borderline at all.  p=0.03, meanwhile, is still pretty strong.

Quote
Further, the significance assumes that "dose reconstruction" is precise, but the dose reconstruction was guesswork, and guesswork made by people who knew the outcome.  If someone is suffering from leukemia, people will be more apt to recall higher dose events, and more apt to interpret events as high dose events.  If someone is in fine health, people will be less apt to recall higher dose events, and less apt to interpret events as high dose.

Recall bias is always a potential issue, and might explain away some of the internal comparison, but no so much the external comparison (the excess risk between liquidators and non-liquidators).

Quote
Even assuming no such bias, some those estimated as being exposed to x amount of radiation, will in fact have been exposed to 10x amount radiation, and others to 0.1x amount of radiation, smearing out any threshold effect. 

Random errors in dose estimation are at least as likely to bias a study's findings towards the null as they are to bias them away from it.

Quote
If indeed those estimated as having 150-300mSv have higher rates of leukemia (and the result was not statistically significant) it may well be because some of those estimated as 300 mSv in fact had 1000 mSv.

Comparing studies that give different results, we see a consistent pattern:  The better the data, the higher the threshold, and the threshold is at least 100 mSv, and quite likely 1000 mSv

Please show me a study claiming a safe threshold of 1000 mSv.

By the way, I did some more research, and found another, more recent paper summing up what's been found among all the different cohorts of liquidators.  Not sure if you'll find it interesting or not, but here you are: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2904977/?tool=pubmed

Their conclusions were pretty conservative: "A significantly elevated OR was seen for all hematological malignancies combined at doses of 200 mGy and above."  (For our purposes, we can think of Grays as basically equivalent of Sieverts, so far as I understand it).

I don't know the facts about routine general medical and dental X-ray's.  Yet I still can't help but cringe when I see children in particular with a cellular phone smashed against their skull. Or using notebooks with high power wireless in their laps.   Why not just have them stand in front of a worn out microwave oven?  Roll Eyes

I wouldn't worry about it.  Mobile phones emit radio waves, not gamma or x-rays, and large epidemiological studies have shown no link whatsoever between use and cancer statistics.

As for medical x-rays etc.: back in the old days, medical X-rays and their sources could be properly dangerous (both Roentgen and his wife dying from exposure, for instance), they are kept to really very safe levels now.  Please see here for a rough comparison of exposure levels: http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/UnderstandingRadiationTopics/DoseComparisonsForIonisingRadiation/

Note that the debate between me and Sam has been largely on the risks of exposures over 100 mSv.  Below that, there isn't much evidence of risk, which is what the threshold hypothesis is all about, and advocates of hormesis claim there may even be some benefit.  And medical scans range from, say, 0.005 mSv for a dental X-ray (meaning that you'd need, oh, about 20,000 of them to top 100 mSv in exposure) to 10 mSv for a full body CT scan (which would very rarely be carried out anyway, and generally only if you had something much more serious than low-dose radiation exposure to worry about).
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