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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Tuesday 8th October 2013

I said, yesterday, that I was working on a piece about what a ‘fatal dose’ really means but another story caught my eye so I’m broadening it to a more general look at some of the things that are wrong but still widely believed.

In part, people seem to cling to discredited beliefs because they want to continue to believe in the subject concerned and are, therefore, dismissive of work that undermines the basis for the belief. But, there is also the question of beliefs that have not been widely discredited because very few people are aware that the basis has been challenged.

I’ll start with e-cigarettes. The active ingredient of plants in the Nicotiana genus, tobacco, is nicotine, widely accepted as a highly addictive substance making quitting very difficult. E-cigarettes have been adopted by people who want to be able to get a nicotine ‘hit’ in places where smoking is not permitted, by people who want to avoid the harms inherent in smoking tobacco but are happy with their nicotine addiction and by those who want to use e-cigarettes as a pathway to breaking their addiction to nicotine completely. There are also claims that previous non-smokers are taking up e-cigarettes.

Nicotiana genus, tobacco

I’ve read some of the many articles about e-cigarettes but I can’t say I’ve reached a settled conclusion about whether they should be encouraged, regulated or banned. But what interested me was that discussions about the desirability, or otherwise, of giving people access to liquids high in nicotine has led to a consideration of what is a lethal dose and how that lethal dose was determined.

The accepted lethal dose of nicotine is said to be 60mg for adults. I’ve always had a problem with that number because lethal doses are measured per kg and 60mg obviously gives very different concentrations per kg for adults whose weight can range from less than 50kg to well over 100kg. I’ve just accepted that ‘small amounts’ can be fatal.

Part of the argument against e-cigs is the small dose of nicotine that could prove fatal. Now, a researcher in Austria, Bernd Mayer, has looked into the origin of the 60mg claim and written an editorial for the journal Archives of Toxicology setting out what he found.

He first looked at the LD50 figures determined in animals and found that these were far higher than the implied LD50 resulting from a 60mg dose for a 75kg adult. Then he looked at a variety of case reports of deaths due to nicotine poisoning and found that they all involved far higher doses. He estimated that the lethal dose might be 20 times higher than the 60mg figure suggests.

Having concluded that the 60mg figure did not stand up, he went looking for its source and found, mostly, that it was one of those numbers that everybody knows, i.e. it had been accepted for so long that it was no longer questioned and cited references to it did not lead to an explanation of its source.

Finally, he found a reference in a book, in German, from 1906 that said that it was difficult to determine the true fatal dose but that it was certainly not more than 60mg. In part this figure was based on some self-experimentation by researchers who, obviously, took a non-lethal dose and recorded the experience. It was those non-lethal doses that led to the estimation of the fatal dose.

Actaea spicata, baneberry

This is similar to the work done by Mrs Alice E. Bacon, in 1903, on the effects of eating Actaea spicata rubra, red baneberry. Mrs Bacon tried ‘a small dose, followed by ‘double the dose’ and then a further doubling of the dose. From the escalation of the seriousness of the poisoning she experienced, she concluded that another doubling, to 12 berries, would be fatal. The Actaea spicata very rarely produces poisonings so there is nothing surprising about the fact that no-one has undertaken modern experimentation to check that claim. Nicotine, however, is a much more widely available poison so it is surprising that almost no work has been done to examine the veracity of the 60mg claim.

It is too early to know if Mayer’s editorial will lead to a widespread re-assessment of the toxic effects of nicotine but it certainly hasn’t had an immediate impact. This morning the BBC report on today’s vote in the EU Parliament on what to do about e-cigarettes spoke about nicotine being a fatal poison in very small amounts so it hasn’t immediately entered the mainstream.

The other accepted claim that was in my mind resulted from the pre-publicity for a new TV programme ‘Trust Me I’m a Doctor’ This programme is, apparently, going to look at some of the things people believe about health that are not supported by evidence. The notion that drinking 2l of water a day is essential is going to the one of the topics. (It isn’t, in case you didn’t know.)

That made me wonder if the series will look at the related subject of caffeine being a diuretic. Many of those who espouse the false idea that you should drink 2l of water a day will tell you that it must be water because drinks with caffeine, like coffee and tea, are diuretics and you will end up more dehydrated that you started.

Here’s what I wrote in October 2011 on this subject.

‘…many people will tell you, as indisputable fact, that coffee is a diuretic. Even doctors, when suggesting an increase of fluid intake, will often say not alcohol and not coffee or tea because caffeine is a diuretic.

‘But, that perception of caffeine comes from a 1928 study involving three subjects whose urination patterns were studied, for a few hours only, before and after drinking coffee. There were no controls i.e. no-one was asked to drink the same amount of liquid with no caffeine present so concluding that the need to wee after drinking a quantity of coffee was due to the caffeine is about as unscientific as it gets.’

There are other examples of dubious information achieving wide acceptance. I’ve written before about Mrs Grieve’s claim that Atropa belladonna, deadly nightshade, berries are ‘insanely sweet’ and how that gets repeated when it is simply untrue.

Rather than blindly accepting ‘facts’ about poisons, it is always useful to consider how those facts arose and if later work has confirmed or debunked the information.


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