CSPI overblows the cancer risk of caramel coloring in soda

The safety of soda has been in the news a lot lately. The news even seems bad for diet coke, which hits close to home for me given my diet coke addiction. The worst seems to be this correlative study proposing a link between diet sodas and stroke risk:

The study, which followed more than 2,500 New Yorkers for nine or more years, found that people who drank diet soda every day had a 61 percent higher risk of vascular events, including stroke and heart attack, than those who completely eschewed the diet drinks, according to researchers who presented their results today at the American Stroke Association’s International Stroke Conference in Los Angeles.

Disturbing news, however, it’s still just a correlative finding from the Northern Manhattan studyand until things are studied more rigorously, I probably won’t quit my current caffeine source. After all, it can reflect patients who are drinking diet drinks because they are diabetic, a known cardiovascular risk factor not excluded in their analysis.
Now the Center for Science in the Public Interest (CSPI) has entered the soda fray with a report suggesting the caramel coloring has unacceptably high levels of a carcinogen called 4-methylimidazole.

An independent study commissioned by the Center for Science in the Public Interest (CSPI) uncovered 4-methylimidazole, or 4-MI, in Coke, Diet Coke, Pepsi and Diet Pepsi at levels 4.8 times greater than those allowed in beverages in California.
4-MI is a byproduct of the reaction that produces the caramel coloring in brown sodas. The chemical has been found to be carcinogenic in animal studies.
The state of California has banned 4-MI in any amount that could potentially lead to one cancer case in 100,000 people. However the levels found in these 4 leading Cola brands indicated a lifetime risk of 5 cancers out of 100,000, assuming that people drink one soft drink per day. That risk rises to 10 cancers out of 100,000 people who drink only soft drinks containing caramel coloring.

But what is the evidence this level of 4-MI could pose a health risk?

A quick pubmed search later and one finds toxicity studies in rats and mice were performed that found no difference in mortality between the groups, but at the higher doses, alveolar/bronchiolar adenoma and carcinoma was found at a higher rate than in the lower dose or control groups in mice and in female rats. But what were the doses? Based on their numbers and the average weight of a rat (300-500g) and a mouse (30g) this would mean a female rat eating 120-150mg of 4-MI a day or mice eating 2-4mg might see a higher rate of these cancers. Now the amount in Coca-Cola appears to max out at 150 micrograms based on the CSPI, and the average weight of a human is 70kg for a dose of about 0.002mg/kg from a can of Coke. So for a human to receive a comparable dose to the lower of the two groups with higher cancer incidence they’d have to drink about 60,000 cans of coke a day. Worse for the CSPI argument some other animal data suggests 4-MI may decrease the rates of some other cancers.
Now, how about the risk calculation cited by the CSPI from California of a 5x increase to 5:100,000? I looked at the califormia prop65 document describing the above study and the basis for their risk calculation cited above. You can read their methods in the appendix themselves, but they basically extrapolate based on size between humans and mice, assume the dose-response is linear, and assume consuming 1/100,000th the dose will result in 1/100,000th the risk. Their estimate of the lower bound of risk in humans would then be 16 micrograms/day. But this estimate is based on a lot of assumptions about effects of lower dosages of the chemical over a longer exposure that strongly skew the minimum safe dose to a tiny fraction of what they gave the mice and rats in these studies.
In other words, 16mcg of 4MI a day is an estimate of minimal risk, based on a few assumptions divided by a huge number. The CSPI however, rather than taking this number with a hefty grain of stroke-causing salt, instead treats these numbers as absolute and reliable indicators of risk and frankly come off a bit kooky:

“Coke and Pepsi, with the acquiescence of the FDA, are needlessly exposing millions of Americans to a chemical that causes cancer,” said CSPI executive director Michael F. Jacobson.

Really? This is a trace exposure of a chemical that has only been shown to cause cancer at huge doses in a model organism. And it sounds like the FDA isn’t buying it either:

FDA spokesman Doug Karas said the findings of the report were not of concern to consumer health.
“A person would have to drink more than a thousand cans of soda in a day to match the doses administered in studies that showed links to cancer in rodents,” he told Bloomberg.

A lot more than a thousand a day. I fully admit I’m not a toxicologist and my knowledge of generating these risk estimates is sparse. Nor do I want to discount taking a “better safe than sorry” approach and being very conservative with needless exposure to risk. But this is on the extreme end of silly to me. You can take almost any chemical we’re exposed to routinely, give rats or mice enormous doses of it, and see increased risks of cancer. These estimates rely on some big assumptions, and after looking at the literature I am not going to worry about caramel-colored sodas based on this report. Frankly, the CSPI comes across as needlessly hysterical over a largely theoretical risk.


8 responses to “CSPI overblows the cancer risk of caramel coloring in soda”

  1. I see ScienceBlogs is STILL in the pocket of big soda.
    (just kidding just kidding)

  2. andre:
    Echoes of Pespsi-gate, perhaps? 🙂
    (also like andre, I jest).

  3. A small correction (that doesn’t change your argument). There’s a general 13:1 conversion for mouse to human dosage that it looks like you may have forgotten (so if a substance has an effect in humans at 1mg/kg it’s often takes ~13mg/kg for a mouse). So, you get around 360-720mg per day for a human to have a similar dose. Of course, that still comes out to an absurd 2400-4800 cans of soda per day.
    Frankly, anyone drinking anywhere close to that much diet coke would have much bigger issues.

  4. Kagehi

    If they want to do something useful, find something to replace the damn phosphoric acid in the stuff with. That actually ***does*** have a known effect, and in common doses. This other gibberish… Hell, I just know the health kooks shopping at work are going to be all over this nonsense, and having no damn understanding of it.

  5. Sometimes the ‘health warriors’ have bought into their own hype a bit too much.
    Why is it so difficult for some to understand the relationship between dose/response?
    Those rats/mice were being fed amounts which are in NO manner representative of any typical (or atypical) human consumption. 6000 sodas a day? That’s over 4 cans per minute. You’d be dead from water intoxication long before you have the chance to develop cancer from 4MI.

  6. lungsucker

    As somebody who drinks at least 3,000 cans of Diet Coke per day, I can say, although a bit bloated and in chronic renal failure, I’m cancer free!
    Seriously, a friend posted this study on Facebook and when I challenged him, I was “being rude.” I’m getting a bit sick of people denying science and also, while were on the subject, the efficacy of Western Medicine.

  7. Colleen

    Regarding what the other commentor wrote about the damn phosphoric acid! You will find less in soda and more in lemonade and orange juice. People should worry about eating and drinking so much. That’s the real problem. We take in way more calories than we need.

  8. Disturbing news, however, it’s still just a correlative finding from the Northern Manhattan studyand until things are studied more rigorously, I probably won’t quit my current caffeine source. After all, it can reflect patients who are drinking diet drinks because they are diabetic, a known cardiovascular risk factor not excluded in their analysis.

    As it happens, I’m a lover of both coffee and tea, and disliked most carbonated sweetened water drinks. I also happen to like my coffee black.
    I’m amazed by this result and other strange associations of diet cola.
    For obvious reasons there are no controlled experiments, and there don’t seem to be strong animal models.
    The “people drink diet cola because they already have health problems or are already gaining weight for other reasons” explanation can’t be ruled out. This seems odd, but the epidemiologic data is just a lot more significant than I would have expected.
    On the other hand, neither can the possibility that diet cola is somehow at least partly contributing.
    More research is needed.
    But coffee and tea are diverse products, and very low cost. (A pound of tea makes 200 cups, so it you buy some of the most expensive tea in the world, you pay less per cup of tea than what a can of diet coke costs, even if you buy your diet coke at Costco).
    It may be worthwhile to experiment with coffee or tea.
    I am not associated with either the coffee or tea industry.

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