by Carl V Phillips
In Part 1 of this series, I described FDA’s proposed rule that would require smokeless tobacco products (ST) to have no more than 1 ppm of NNN (a tobacco-specific nitrosamine or TSNA) dry weight. I discussed some of the political and policy implications of this, and reasons why the rule will probably not survive. I also noted that almost no current products meet that standard, and that American-style ST probably cannot meet it. Despite the proposed rule probably being mooted, I noted there is still value in examining just how bad the ostensibly scientific analysis behind it is. In Part 2, I noted that the FDA’s estimate the standard would save 115 lives per year is premised on their estimate for the risk of oral cancer caused by ST use. But, in fact, the evidence does not support the claim that ST use causes any oral cancer risk. I then focused on why, even if one believes there is some such risk, the method used to calculate FDA’s quantitative estimate is utter junk science.
So far, none of that has addressed NNN itself, and how meeting the NNN standard would affect the carcinogenicity of ST, if it is carcinogenic. It turns out that this part of FDA’s analysis is even worse than that discussed in Part 2.
Estimating the health effect of a quantitative standard for an exposure is a matter of estimating the relevant range of the dose-response curve, along with knowing how much people’s dosage would change. That is, you need estimates like, “N people use product X, which has 5 ppm NNN, which causes Y risk per person, versus the Z risk per person from 1 ppm, so multiply N by (Y-Z)….” With such numbers we could estimate the effect of an adjustment in the NNN concentration.
In reality, it is not that simple. In Part 1, I pointed out that most products could not just have their NNN concentration “adjusted” like that, and that they would have to be fundamentally changed, effectively eliminated and replaced in the market (perhaps if FDA had not made the arithmetic error noted in Part 1, that would only be “some” rather than “most”). Many consumers of the eliminated or fundamentally altered products would not be happy with the new option. Some would just quit, eliminating the Y risk as well as any other risk from using the product (setting aside that as far as we know are both nil; remember, we are down that rabbit hole here). Some would switch to smoking, creating a risk that is orders of magnitude greater than anything discussed so far, making all of the details moot: the net health impact would be an increase in risk.
But that is the simple practical criticism of this madness, one that hinges on questions of consumer behavior (an area where FDA’s analyses are consistently absurd, but they always manage to trick their audience into accepting their assertions). That is not what I am doing here, though I suppose I just did it in one paragraph. My goal is to point out that the FDA core claims about benefits here are based on junk science, setting aside the enormous costs that would dwarf them anyway. So returning to my point here, what basis do we have for estimating Y, Z, and other points along the dose-response curve?
Indeed, we do not even know that NNN in ST affects cancer risk at all.
As I mentioned in Part 1, if you are only familiar with the rhetoric about this topic, and not the science, you would be forgiven for not knowing that the assertion there is any such effect is based only on heroic extrapolations and assumptions. You might further surmise that since FDA claims that this reduction would reduce cancer deaths by 115 per year (note: not “about 100”, but as precise as 115), there is not only evidence that NNN in ST causes cancer, but there is also so much evidence that we can precisely estimate a dose-response.
What we know about NNN and cancer is based on biological theory (we have evidence that some nitrosamines cause cancer in humans), and the effects of exposing rats, hamsters, and other critters — species whose propensity to get cancer from an exposure is often radically different from ours, and even from one another’s — to megadoses of NNN. Those toxicology studies do suggest that NNN exposure probably causes cancer in humans, in a big enough dose, and under the right circumstances. Of course, that is also true for almost everything. When IARC, the cancer research arm of the WHO, made their blatantly-political decision to declare NNN a known human carcinogen, they did so in violation of their own rule that there has to be some actual human exposure evidence before making such a declaration. There is not. But even if someone believes that NNN in ST does cause cancer in humans, the rodent megadose data obviously does not tell us anything about the effect of the reduction in dosage imposed by this rule.
Stepping back, it is useful to understand the potential legitimate use of toxicology studies like those. They — or, better, in vitro studies of cells that are actually similar to the human body and do not require sociopathic torturing of innocent animals — are useful for giving us a heads-up that a chemical or combination of chemicals might be carcinogenic or poisonous. This might be a good reason to undertake the more difficult search for epidemiologic evidence that the real-world version of the exposure is causing the bad outcome. Or at least a reason to pursue the in-between step of looking for biological evidence of harm from the real-world exposure in humans. It might even be sufficiently compelling to prohibit introducing a novel exposure, acting before we can even get any human data.
If toxicology studies of a chemical all fail to produce a bad outcome, this strongly suggests that the exposure will not cause the harm, so long as that failure is consistently confirmed using various toxicology methods (claims that a single toxicology study shows that an exposure is harmless, which are currently appearing in the pro-vaping rhetoric, are misguided). But getting a bad outcome in a particular toxicology study does not mean that the real-world exposure actually does cause harm. The pattern in the toxicology has to be far better than what we have for NNN before such a conclusion is justified, including getting the effect at reasonably realistic exposure levels and fairly consistently across a variety of methods.
Consider an analogy: We are interested in knowing whether there is life on other planets, but actually going there to take a look is rather difficult. We have a much cheaper tool in our toolbox, however, which is to use modern telescopes to see if light scatter suggests a water-rich atmosphere. Of course, that is far short of observing life; it would be insane to say “we saw evidence of water, so there must be life there!” But since the versions of life that we understand require there to be enough water, seeing that creates the intriguing possibility of life. Failing to find water tends to rule out the possibility of life as we know it.
Another legitimate use of toxicology is to tell us why an exposure is causing harm. Of course, this should mean there is evidence of harm, not just some wild assumption that there is harm. Continuing the analogy, pretend that someone looked at the light scatter around Mars and claimed they saw enough water to support life: “Aha, this shows that the canal-building civilization is water-based life as we know it.” Um, but you do know that early 20th century telescopes debunked that 19th century canals myth, right? Also we have had numerous close observations of the planet and little labs driving around on the surface. Your hint about the possibility of life is utterly pointless given that we have much better information about the reality.
I have often described the TSNA toxicology research, which inexplicably continues to this day, as an attempt to identify which chemical pathways cause a cancer outcome that does not actually occur. As with Mars not having canals, we know that ST use does not cause a measurable risk for cancer, and therefore the NNN and other TSNAs in ST are not causing a measurable risk (unless we think that other aspects of the ST exposure prevent exactly as much cancer as the TSNAs cause, something that no one is seriously proposing). One possibility that has been seriously proposed — e.g., by Brad Rodu, whose work I cited in Parts 1 and 2 — is that something else in ST, perhaps antioxidants, directly negates whatever cancer-causing effect the TSNAs might have if we were exposed to them alone (which does not happen at a level beyond a few stray molecules). Indeed, when the exposure is tobacco extract, those rodent studies fail to show the carcinogenic effect from NNN, or anything else in ST for that matter, a fact that is conveniently glossed over.
So how did we end up with the “fact” (which I suppose should be called the fake news in current parlance) that NNN and other TSNAs in ST cause cancer? It basically comes down to circular reasoning, or perhaps it is figure-eight reasoning since there are two circles as well as a few other fallacies. It goes something like this (and I am really not exaggerating):
“Given that we have only seen an effect in megadose rat studies, how can we really be sure that TSNAs at the relevant dosage and in a realistic exposure cause cancer?”
“Because smokeless tobacco causes cancer, and it contains TSNAs.”
“But [even setting aside that we do not know that is true] how could you know it was the TSNAs causing it.”
“Because we know TSNAs cause cancer.”
“Um, isn’t that so transparently circular that even tobacco control’s useful idiots will see right through it?”
“There is more. We know that higher-TSNA products cause more cancer risk.”
“Ah, now that sounds like actual evidence. Please explain.”
“US products have higher TSNA levels than Swedish products, and US studies show a cancer risk while Swedish studies do not.” [Note: see appendix to this dialogue, below.]
“But didn’t you read Part 2 of this series? That contrast does not appear in studies of modern US products, but only from a few studies of an archaic type of product.”
“Yes, exactly. That product was very high in TSNAs, and its cancer effects were off the charts compared to modern products. Case closed.”
“There are no measurements of the TSNA levels of those archaic products. How do you know they had high TSNA levels?”
“Isn’t it obvious? They must have, because they caused cancer and TSNAs cause cancer.”
Loopity loopity loop.
In fairness, there are honest observers, including Brad Rodu, who hypothesize that this is indeed the reason the archaic products apparently caused cancer. But this is just a hypothesis, and it cannot be tested. Indeed, we cannot even replicate the basis for claiming those products caused cancer in the first place. It basically comes down to a single study from the 1970s — not exactly overwhelming evidence.
A bit more useful background: In the 2000s, the anti-ST crusaders in and funded by the US government (CDC and NCI, before FDA joined the game) fought a rearguard action against the evidence that had emerged from Sweden that ST was approximately harmless. Part of this was insisting that the higher levels of TSNAs in US products meant that the Swedish evidence was not informative. It was political bullshit on its face. Still, I wrote an analysis over a decade ago that showed that the ST products that produced those null results in Sweden had about the same TSNA levels as then-current US products. (This was based on limited analytic chemistry from before 2000. There were only a handful of TSNA concentration studies in the public record. But there was enough to show this.) TSNA levels in all styles of ST products were and are decreasing over time. It might have been true that 1990 US products were materially more hazardous than 1990 Swedish products (which showed no measurable risk) because they had higher TSNA levels. But mid-2000s US products had low enough TSNA levels that this would have no longer been true. This leads to the appendix for the dialogue. We could imagine this variation:
“US products have higher TSNA levels than Swedish products, and US studies show a cancer risk while Swedish studies do not. Also there is a time trend, wherein TSNA levels have been dropping in both US and Swedish products, and older studies found elevated cancer risks, while newer ones do not.”
“Part 2 of this series dismisses your first sentence. But the second sentence makes some sense, though it might just be because the older studies used really primitive methodology. Still, you have a prima facie valid point there, unlike all your other complete bullshit. But, hey, doesn’t that also mean you are conceding the fact that modern ST products do not cause any measurable cancer risk, even if older products might have?”
“Er, no. We never said that. We never made any claim about time trends despite it being the most scientifically defensible argument we have. Strike all that from the record.”
Summarizing this, we have only unsupported hypotheses and circular reasoning behind the claim that NNN in ST causes any of the (quite possibly zero) cancers caused by ST. Given this, we obviously know nothing about how much cancer a particular concentration of NNN causes. That is sufficient to show that FDA’s claim cannot possibly be science-based. But I am sure you share my curiosity about how FDA took this complete lack of information and turned it into the conclusion that exactly 115 lives per year would be saved by this regulation.
Here it is (from the proposed regulation):
….increase in oral cancer risk of 116 percent among smokeless tobacco users compared with never users. We then reduce this value by 65 percent based on toxicological evidence relating the estimated average reduction in the dose of NNN to lifetime cancer risk under the proposed standard. The result is a reduction in the estimated relative risk of oral cancer to 1.41 under the proposed product standard. FDA used the following calculation: (1 + (2.16−1) × (1−0.65) = 1.41) for this determination.
Thanks, guys, for showing us how to do that arithmetic so I did not have to find a third grader to ask. The important bit of showing their work, of course, is about justifying the inputs. In the introduction, FDA refers the reader to section IV.C for the basis for the .65 figure. It is really section IV.D, because, hey, just because you spent a million dollars writing a regulation that is potentially devastating for industry and millions of consumers does not mean you should bother to have someone edit it. It turns out the assumption is that the dose-response is linear across all quantities, and under that assumption the effects observed from megadoses in rodents gives a dose-response that translates into .65. The generic problems with this include the fact that the linear (also known as “one hit”) model of carcinogenesis has long-since been dismissed as invalid, the folly of extrapolating orders of magnitude beyond the observed data, and the little matter that rodents are not people.
It gets worse still when you look at the equation that FDA used to calculate the fictitious linear trend. (And I am not referring to the fact that they actually cut-and-pasted the equation in their document as an image from some low-res PDF of someone else’s document. This is not a scientific flaw, of course, but, it does suggest the proposed rule was written by people who have so little education and experience in science that none of them had ever learned how to typeset a simple equation.) The equation builds in the assumption that a very high exposure for a short time (e.g., what the rats experienced) has the same effect as the same total exposure stretched out over many years. This is the linearity assumption taken to the extreme. It not only assumes linearity for each parameter — i.e., increasing years of exposure, increasing quantity per exposure, or increasing number of exposures per day by Y% increases risk by Y% — which is completely unsupportable and almost certainly wrong. It also assumes a multiplicative effect for all interactions, which is also unsupportable and almost certainly wrong. For those who did not follow that, I will explain its major implication: The assumption is that a given lifetime quantity, X, of NNN exposure creates the exact same total cancer risk whether it is consumed all in one day, or one month, or spread out over 70 years. It is the same whether an ongoing exposure takes place all at once each Monday morning or it is spread evenly throughout the week. Moreover, if you increase X by 10% it increases the risk by 10% no matter how the consumption is spread out. On top of all that, if someone’s body mass is 10% lower his risk from X is always increased by 10%. If his mass is 99.963% lower (i.e., he is a hamster and not a human) then the risk is increased exactly 2720-fold.
Such simplifying assumptions about linearity and multiplicativity are not terrible if you are interpolating (i.e., you have data from both sides of the quantity you are assessing and you are trying to fill in the middle) or are extrapolating a little bit beyond the range of your data. But in this case they are extrapolating orders of magnitude beyond the rat data. Weeks of exposure rather than decades, 30 g bodies rather than 75 kg, and crazy large doses. And, of course, there is the little matter of assuming that a different exposure pathway in a different species has the same effect of ST exposure in humans. The huge extrapolation means that the slightest departure of the assumptions from reality (and it is safe to say that the departures are more than slight), means that the final estimate is complete garbage.
It gets worse. The key parameter is what is multiplied by the total lifetime units of exposure in order to estimate risk, which FDA calls the “cancer slope factor” or CSF if you want to search for it in the document. For this, they rely entirely on a 1992 estimate from the California EPA, which itself was based on the results of a 1983 paper that looked at what happens when hamsters were given huge doses of NNN dissolved in their drinking water. Yes, really. FDA’s number ignores the ~99% of the relevant research that has been done in the last three decades, and it was obviously pretty sketchy even in 1992 given that it was based on a study whose real information value (about actual human exposures) was approximately nil. Moreover, there is this:
As defined by the EPA guidelines, the cancer slope factor (CSF) is “an upper bound (approximating a 95percent [sic] confidence limit) on the increased cancer risk from a lifetime exposure to an agent.
So apparently (the methods are reported so poorly that it is hard to be certain) they not only based this key number on evidence — to use the word rather loosely — from a single ancient toxicology study, but they did not even use the actual estimate that was generated from that. Rather, they used a larger number generated via an arbitrary process. The upper bound of a 95% confidence interval is a completely meaningless number in this context. There is an argument (which many would call dubious) that some arbitrary inflation of the point estimate like this should be used in “abundance of caution”-based regulations. (Update: More on this in my follow-up post.) But it is not an estimate of the actual effect. I know this seems like an arcane technical point in the context of everything else, but I cannot stress enough what an enormous failure of legitimate science this is (assuming they did what it sounds like they did). This would mean, for example, if there had been fewer observations collected in that 1983 study, but it had still supported exactly the same point estimate, FDA would be claiming some larger number of lives saved, like 125 per year rather than 115.
When presenting this number, and practically admitting it is junk (despite using it to calculate their estimate of 115 to three significant figures), FDA writes:
FDA welcomes public comment on whether there is a more robust CSF available for NNN.
This is a classic bit of anti-scientific rhetorical strategy. Anyone answering that question as phrased is implicitly conceding that the estimate FDA used has some validity. Respondents are effectively conceding that if they cannot make a compelling case that some other number is better, then FDA’s number was appropriate to use. When a question’s phrasing builds in invalid assumptions, or when it assumes away the really important questions (“Have you stopped beating your wife?”), the response needs to unask it, not answer it. So here is my unasking answer to their welcoming of public comment:
The number FDA used has absolutely no hint of validity. However, there is no robust, or even remotely plausible basis for generating this “CSF”; any number used here might as well be made-up from thin air. That said, given that ST does not seem to cause oral cancer in the first place, the best default estimate is zero. There is no legitimate basis for concluding an estimate of zero is wrong. Oh, and also if you are going to use a junk-science extrapolation from rodent studies, you should at least calculate this number based on all such studies to date. If you are not capable of doing that analysis, and instead are limited to using the approach any middle-school student would use if confronted with this question (run a search and blindly transcribe whatever someone once wrote), then you have no business regulating anything!
I’ll take a deep breath here, because that is still not all. Look back at that grade-school arithmetic they showed us. Notice any assumptions embedded in it? Yes, that’s right, they assumed that all the cancer risk that they claim is caused by ST is caused by NNN, and thus a .65 reduction in the risk from NNN exposure is a .65 reduction in total risk. Wait, what? FDA did some hand-waving in their document about reductions in NNN also carrying along reduction in another TSNA, NNK, but they never tried to justify the claim that the (supposed) cancer risk was all due to NNN or even NNN plus NNK. How could they?
Effectively, FDA has just declared that they believe that whatever the cancer risk (at least oral cancer risk) is caused by ST consumption, it is all caused by TSNAs and no other molecules contribute any cancer risk. They never suggested this was a simplifying assumption. This could have some amusing implications. The next time you see one of those anti-scientific bits propaganda about ST containing 27 carcinogenic chemicals (or whatever number they are making up that day), you can reply that FDA has declared that at least 25 of those do not actually cause cancer. On the other hand, we should probably not try to push this too hard on this. I am guessing that, given all the other errors, the authors of this rule did not understand their own arithmetic sufficiently to know they were implicitly declaring this to be true.
Returning to the life on Mars metaphor, and the dialogue motif, the “logic” behind the FDA analysis would map to something like the following:
“From my light-scatter observations, I have concluded that had the water density in the martian atmosphere been X, instead of the Y I observed, the civilization that built the canals would not have collapsed just after helping humans build the pyramids, but would have thrived for 1,150 more years.”
“Wait, what? There are no canals. There was no civilization. Ancient extraterrestrial visitation stories are just silly claims by people who do not understand science and technology. The rovers and other Mars exploration have already shown that if there is or was anything we might call life, it has had no perceptible impact, let alone built a civilization. There is not enough water to support an ecosystem now, and was not enough 5000 years ago. But even if there had been a civilization, there is obviously no basis for estimating how atmospheric water density affected it, let alone a way to predict its demise to three significant figures based on one observation. As a minor point, I am not sure from what you said whether you meant Mars years or Earth years, but I am guessing you do not even know they are different.”
I am not being hyperbolic when I say FDA’s proposed rule comes across as parody. It reads like someone concocted it in order to ridicule a collection of faulty common practices and reasoning in public health science, creating cartoon versions to highlight problems that are often subtle. Please reassure us, FDA, that this was intentional. Even more so, those of you at the Center for Tobacco Products might want to reassure your colleagues elsewhere in FDA that this is not what their once respectable agency has come to.
Alternatively, perhaps it was really a joke by outgoing officials, hoping for a *popcorn* moment when the new administration tried to defend the rule in court. Or maybe it was just a Dadaesque tribute to the day it was issued. I realize these do not seem like terribly likely explanations, but they are more plausible than believing that anyone with a modicum of scientific expertise thought that this hot mess was legitimate analysis.
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It might have been true that 1990 US products were materially more hazardous than 1990 Swedish products (which showed no measurable risk) because they had higher TSNA levels. But mid-2000s US products had low enough TSNA levels that this would have no longer been true
They found the fault was in the curing and rectified it by 2001, something I have never found mentioned anywhere but American Agricultural Colleges.
Retrofitting Tobacco Curing Barns
“Recent research has shown that a class of carcinogenic (cancer-causing) compounds known as tobacco specific nitrosamines (TSNAs) may be formed in flue-cured tobacco leaves during the curing process.
These compounds are not found in green (uncured) tobacco. Present research suggests that TSNAs are formed through a chemical reaction between nicotine and other compounds contained in the uncured leaf and various oxides of nitrogen (NOx) found in all combustion gases, regardless of the fuel used. Eliminating NOx compounds in the curing air by using a heat exchanger system has been shown capable of reducing TSNAs to undetectable levels in cured tobacco.
The direct-fire curing systems currently in use in most U.S. curing barns are considered to be the major factor contributing to elevated levels of TSNAs in U.S. flue-cured tobacco. Further, there is no known fuel treatment or burner design that can eliminate these nitrogen compounds from combustion gases without the use of a heat exchanger (found in all indirect-fired systems). It is believed that reducing the levels of TSNAs in tobacco products would reduce some of the health concerns associated with tobacco use.
To receive price support for tobacco grown in 2001 and thereafter, producers must retrofit, or change, all barns used to cure the crop to operate with indirect-fired curing systems. An indirect-fired system passes the combustion gases through a heat exchanger and out of the barn, thereby preventing the mixing of flue gases with curing air.
Systems with the combustion entirely outside the barn and that conduct the heat to the barn with hot water or steam have proven entirely satisfactory for reducing TSNAs and are acceptable.
Research during the 2000 curing season has shown that converting from direct- to indirect-fired curing can reduce levels of TSNAs in cured leaf to below detectable levels (less than 0.1 part per million).”
Surely, any studies on TSNAs in American fired cured smokeless tobacco from before 2001 should be considered only of historical interest.
That seems to be correct at the flyover level, though wrong in many of the details (notably including the claim that TSNAs are not present in uncured leaf). Leaf variety, curing method, and several other factors affect TSNA levels.
I am not sure I would describe as a “fault” a classical engineering process that could, by then, have been changed to make a product that is higher quality by one measure. It is like saying “the fault of old factories was not using enough robots”.
Is the epidemiological evidence statistically powered enough to rule out the small effects predicted by the toxicology?
Well, first off it is not accurate to say that the toxicology predicts small effects. It is like saying that a light scatter measure predicts the survival of martian civilization: Yes, you could make up some (never validated, obviously) equation and call whatever it spits out your prediction. You could also say it was “calculated” and “estimated”. But these are all misleading. The number is just made-up and then dressed up with claims to trick the reader into thinking it is something else. It goes too far to say this toxicology “predicts there is SOME effect”, let alone to quantify it.
But the question about what the epidemiology could show, with respect to FDA’s made-up number, is still a good one. The answer about REALITY is: Yes, the epidemiologic evidence is sufficient to rule out the FDA claim, for the reasons I gave. Namely, the risk from the current product mix is not nearly a doubling of OC risk. But you could still ask the hypothetical question, “IF it were really the case that 3 ppm (dry) difference changed rate of caused OC by a factor of 2, could we detect that effect, PRETENDING it were the case that the average product on the market ~doubled the OC risk”. The answer to that is yes, though you would need better quality (more honest) research than has been done. If you had about the same number of studies that exist now, but they were high quality and honest, then you could do a meta-analysis and detect that effect (based on best guesses about the average NNN density from each study’s exposure, since that is be missing from the epi). Note that I mean a legitimate meta-analysis, one that compares the results of studies and, in this case, looks at how they differ by NNN density — not a junk synthetic meta-analysis. With the hypothetical numbers, you would probably be able to spot the trend and conclude that NNN density made a difference in the range, though obviously you would have some measurement error.
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