As anyone who has been watching the news will have realised, for a lot of pupils, it hasn’t been the smoothest start to the new school year. Yet, crumbling classrooms and failing concrete aren’t the only health risks that our children are exposed to at their primaries and comprehensives, if a recent headline in the Guardian is anything to go by:
Thousands of schools serving meals that could contain cancer-causing chemicals
Education authorities across England and Wales shown to use meat that has been treated with either nitrites or nitrates
As the Guardian explains, Local Education Authorities have stated that “some or all of the schools in their area are using meat that has been treated with either nitrites or nitrates”. Typically, that’s likely to be bacon or ham, as nitrates and nitrites help give those meats their flavour and pink colouring. They also act as preservatives, slowing down the bacteria that cause food spoilage. Nitrates and nitrites are naturally occurring chemicals, and when it comes to pork products they’re often part of the curing process.
As the Guardian article continues, schools are using these treated meat products as part of school lunches, even though there is “evidence that both chemicals … can be carcinogenic”. The Guardian also mentions that some scientists and politicians are calling for nitrites and nitrates to be banned from use in meat production. It’s clear that we are meant to be very concerned about the thousands of schools serving up cancer-causing chemicals to our children, or at least to the children not actively dodging falling concrete.
But how worried should we be about all of this? To answer that question, the Guardian cite an earlier article in the paper, from December 2022, to back up their fears over these cancer-causing chemicals.
‘Too much’ nitrite-cured meat brings clear risk of cancer, say scientists
A leading scientist has urged ministers to ban the use of nitrites in food after research highlighted the “clear” risk of developing cancer from eating processed meat such as bacon and ham too often.
The study by scientists from Queen’s University Belfast found that mice fed a diet of processed meat containing the chemicals developed 75% more cancerous tumours in the duodenum than mice fed nitrite-free pork.
It also found that mice fed nitrite-cured pork developed 82% more tumours in the colon than the control group.
This story made a lot of headlines and a lot of splash at the time, with some even linking it to the WHO’s decision in 2018 to label processed meats a Group 1 carcinogen. Putting the WHO aside for a moment, it’s worth looking at the new study that was the inspiration for these stories: a 2022 study in The Nature Partner Journals Science of Food, titled “Dietary inclusion of nitrite-containing frankfurter exacerbates colorectal cancer pathology and alters metabolism in APCm in mice”.
This is an animal model, in which researchers took 40 Adenomatous Polyposis Coli (APC) Multiple Intestinal Neoplasia (min) mice – these are mice that are highly prone to developing tumours, making them handy to research what causes tumours to develop or not.
The researchers split the 40 mice into four groups, each of which got unrestricted access to foods, aligning to one of four different diets: nine mice were given a diet containing unprocessed nitrite-free pork, ten were given a diet of nitrite-free sausage, ten were given a diet of nitrite-containing frankfurter, and the remaining nine were given a control diet of AIN76 – a special kind of rodent chow that is used in research. The paper doesn’t explain what happened to the two missing mice, but we can assume that isn’t important.
In each of the meaty diets, the mice had unrestricted access to food pellets consisting of 15% of their specific meat, and 85% of the basic chow. So, in summary, 28 of the mice received various nitrite-free diets, and 10 got the nitrite-containing Frankenfurter.
After 8 weeks, the researchers culled and dissected the mice, to see how many tumours each had developed, in either the duodenum, jejunum, ileum or colon. What they found was, on average, the nitrite free pork and nitrite free sausage mice developed around 8 tumours each, while the nitrite-rich frankfurter mice developed around 11 tumours each. The control mice had an average of 7 tumours each – because, after all, these were mice selected especially for their propensity to develop tumours. In fact, in the Jenunum, the control mice developed more tumours than any of the other mice, and in the colon, it was the nitrite-free pork that correlated with the most tumours – neither of which were statistically significant findings.
Of all the various analyses that were undertaken, the only significant finding here was that, compared to control, the nitrite-processed frankfurter mice developed a statistically significant number of additional tumours. The pork and sausage mice did not develop a statistically significant number of additional tumours above control.
In the discussion, the authors conclude:
This study found that a modest inclusion of a sodium-nitrite-containing pork frankfurter in the diet of APCmin mice significantly increased the number of intestinal tumours present. A similar inclusion of either nitrite-free pork sausage or minced pork did not increase tumour numbers.
It was this finding in particular that inspired the headlines in the Guardian and elsewhere, about the cancer-causing chemicals in your children’s foods. To reiterate, that scary headline is based on a study in which ten nitrite-fed mice who were prone to developing intestinal tumours developed more intestinal tumours than tumour-prone mice fed on a non-nitrite diet.
This might be a robust study, with a reliable finding, even despite the multiple analyses conducted. However, this finding is based on 10 mice, out of a total of 38 mice, all of which were already prone to developing tumours. It might prove to be a useful starting point, but it’s not sufficient yet to justify alarmism over diets in schools.
What’s more, that discussion might be making a claim that is not entirely supported, in that it described the Frankenfurter diet as “modest inclusion” of sodium-nitrite-containing pork frankfurter. The “modest inclusion” amounted to 15% of the mice’s diet, supplemented with 85% of other feed. Would we otherwise consider 15% of dietary intake a “modest” amount of processed meat? Would we expect cured sausages and bacon to make up 15% of food intake per day, every day? That seems like an unusual amount of processed meat.
On that subject, it is worth revisiting the WHO labelling issue, where the WHO moved processed meat into the Group 1 carcinogen category. Group 1 are the things that are known carcinogens to humans, and there are 127 things in that list, compared to 95 things that are Group 2A “probably carcinogenic”, and 323 in Group 2B “possibly carcinogenic”. In 2018, processed meats were moved into group 1. But just because something is a cancer risk, that doesn’t mean it’s something we should be scared about, depending on the risk level.
Helpfully, the WHO do actually quantify that risk for us:
The consumption of processed meat was associated with small increases in the risk of cancer in the studies reviewed. In those studies, the risk generally increased with the amount of meat consumed. An analysis of data from 10 studies estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%.
Coincidentally, 50 grams is about the size of a Vienna Frankfurter, at least according to the Sausage Sizes Guide on the website sausageman.co.uk. So, if we are to listen to the WHO’s own data, and if we are to take the sausage man at his word, then someone would have to eat an additional Vienna Frankfurter every day in order to raise their risk of colorectal cancer by just less than a fifth.
The current lifetime risk for colorectal cancer in the UK is about 5%, according to cancer.net – therefore, if you eat a regular diet, with a regular amount of processed meat, and then you add a daily additional smoked sausage to your diet, your lifetime risk would rise from 5% to 6%.
The question we should be asking, then, is how many sausages are schools giving our children, and at what frequency. And, more generally, what percentage of our kids’ daily diet is made up of nitrite-processed meat. We also should not panic just yet, because so far the claims around the harm of nitrite-processed meats are only in mice – but we should avoid excess until there’s better data out there.
On the subject of data, there’s one final coda to this story. There’s a reason that this story came out at the start of September, with the scary headline about “Thousands of schools serving meals that could contain cancer-causing chemicals”. The schools did not announce this as part of a statement about new school menus for the year ahead – the story came from LEAs responding to freedom of information requests about the nitrite content of their school meals. The source of that FOI is named in the Guardian’s coverage:
The FoI exercise was undertaken by Finnebrogue, a Northern Irish food firm that launched the UK’s first brand of nitrite-free bacon – Better Naked – in 2018.
Jago Pearson, the company’s chief strategy officer, said it welcomed other food producers, including Waitrose, Morrisons and Marks & Spencer, introducing similar products “because this can only help improve the health of the nation”.
This, therefore, is a story about how your child’s school meals contain carcinogenic chemicals that you should be scared of… yet, it is arguably a tool for a nitrite-free meat manufacturer to get some eye-catching headlines to endorse the primary selling point of their product. Meanwhile the story may scare readers over what amounts to indicative early research in a small number of tumour prone mice who were fed an unusual amount of nitrite-heavy food.
It may well turn out, in time, that nitrite in processed meats are bad for us, and raise our cancer risk from 5% to 6%. Or it might turn out to be one of those “in mice” findings that don’t pan out when it comes to data in humans.
In either case, school dinners are not currently the biggest threat to the health and wellbeing of children at school in the UK, and parents have enough to worry about without also panicking about the contents of that relatively rare smoked sausage.
The post Not right about nitrites? Mouse study provokes media scaremongering over cured meat appeared first on The Skeptic.