I’m not sure that there is anything more bamboozling to the general public than journalists drumming up academic papers for nutrition segments. “Scientists say that caffeine causes cancer, or maybe it prevents it?” “Or was it the nitrites in your bacon or the nitrates in your water?” “No, wait, it was more than two glasses of wine per week and you are toast”. “Find out after the break if your charred toast will give you cancer”. It is an absolute minefield out there.

So it might surprise you to discover that the list of scientifically-agreed carcinogens (things we know cause cancer) is actually remarkably concise. The International Agency for Research on Cancer (IARC), run by the World Health Organisation, lists 121 known human carcinogens. Chinese-style salted fish is the only food that makes the list. Recreational choices such as alcohol, tobacco, the areca nut and combined estrogen–progestogen oral contraceptives are also listed as known carcinogens, but it is probably a little unhinged to describe these as food. Most of the list is made up of pharmaceuticals, viruses and radiation types that you are likely already doing your best to avoid without any scare-mongering from the television. The list also includes occupational carcinogens such as arsenic, asbestos, chromium, nickel compounds, leather/wood dust, soot, and diesel engine exhaust fumes.

So how does the scientific community decide if something causes cancer and why is there so much extra chatter going on? First, let’s briefly look at what cancer is.

What is cancer?

When things are going swimmingly, the cells in your body are under tight regulation. Each cell is a highly specialised worker happily living in its place of employment. When the cell becomes too old or sustains too much damage, it is sent a signal from its own broken machinery or, possibly, from one of the neighbouring cells who has noticed that all is not right on the other side of the fence. The signal means that it is time to call it quits. The cell then dies a very orderly death via a mechanism endearingly referred to as apoptosis.

Cancer happens when one of your cells goes rogue and stops listening to the regulation signals. This is essentially a genetics problem, the DNA in the cell has mutated to a form that is immune to the usual signals for growth regulation and apoptosis. These mutated cells become immortal – which is a hell of a lot less useful than it sounds. Often these dysfunctional cells are dealt to by the higher authorities such as the immune system, or they occur in isolated or slow growing cells that can’t get up to too much mischief. 

But, in the worst case scenarios, these cells are fast growing and are in a very critical area of your body. The unluckiest place would probably be the brain stem, with the heart, lung and pancreas not too far behind. However, these rogue cells usually start off somewhere where they are reasonably well tolerated and then eventually migrate to new areas of the body via the bloodstream. When the rogue cells get in the way of the well-behaved cells that are doing the real work, that is when we have the disease that we all refer to as ‘cancer’.

What causes cancer?

A mutant cell can happen purely by chance. Each time a new cell is made, the cellular machinery has to copy every scrap of DNA in the genome. Here, there is an opportunity for the cellular machinery to make a mistake and introduce a fresh mutation. Some DNA sequences are more difficult to get correct every time and therefore prone to mutations. Think of this like a phone number that is full of ‘6’s and ‘9’s or one of those tongue twister sentences. Some families, unfortunately, have genes that read like “she sells seashells by the seashore” and that can lead to an inherited cancer risk. Others have inherent weaknesses in the cellular machinery that is supposed to keep an eye on genetic damage such as breast cancer gene (BRCA) mutations.

And sometimes something gets into the cell and damages the DNA or the machinery that deals with the DNA, causing the mutations that kick-start the cancer process. Certain chemicals, viruses and radiation are known to have genotoxic (i.e. toxic to genetics) effects that cause cancer and these are known as carcinogens. But how do we know something is carcinogenic?

How do we tell if something causes cancer?

Let’s start off by acknowledging that cancer research is in no way complete. In many ways it is still in infancy. The IARC only started its working groups back in 1970, that’s long enough for bell-bottomed jeans to come back in style three times, but just a blink of an eye for biological research.

That being said, it is usually straightforward to test if something is very genotoxic. Take some cells, expose them to the possible carcinogen and see if the DNA in the cells changes. This can be backed up with some animal research where hapless lab animals are exposed to the possible carcinogen and monitored to see if they develop cancer. Spare a thought for all the lab rats that have been forced to smoke cigarettes or endure reenactments of the Chernobyl disaster. If something is overtly carcinogenic then it will be obvious with some basic, but brutal, labwork.

Things get murky when we try to tease out potential carcinogens that have a smaller or indirect effect on DNA. Particularly if these are lifestyle factors such as nutrition. It is difficult to douse cell cultures or lab animals in, say, cheese burgers. Scientists only nabbed Chinese-style salted fish because it was so carcinogenic that small extracts of it were enough to mutate bacteria. The urine from rats fed Chinese-style salted fish was able to do the same and there is some evidence the Chinese-style salted fish compounds can reactivate the Epstein–Barr virus which is a known carcinogen itself. Plus, the small problem of people who were partial to Chinese-style salted fish contracting nasopharyngeal carcinoma.

 Nitrates and nitrites, and a great deal of chatter

Let’s take a look at a topical example for the farming community. Nitrates and nitrites have been getting a bit of a public flogging lately. I can tell you, unequivocally, that they should not be at high concentrations in your drinking water, but are they actually carcinogenic? 

Well, I would say that the jury is still out, but there is not even enough evidence to lay charges.

Nitrates and nitrites are naturally occurring compounds in your food. They may also be added to processed foods to prevent harmful bacterial infections in items such as processed meats. Nitrates are compounds that have a nitrogen joined to three oxygen atoms (NO3) and are relatively inert. Nitrites have one fewer oxygen atom (N02) leaving more hands left to party and are therefore a bit more reactive than nitrates. Nitrites such as sodium nitrite and potassium nitrite tend to be the more commonly used preservatives for cured meats like bacon.

Nitrates and nitrites are not, in themselves, carcinogenic. The bulk of the debate is centred around whether your body converts nitrates and nitrites into meaningful quantities of a chemical group called N-nitrosamines which are known carcinogens. Your body definitely makes some N-nitrosamines because these are essential for cell signalling, but could eating too many nitrates/nitrites lead your body to make an excessive amount that might be carcinogenic? 

Well, that is the question. The debate is mainly centred around epidemiological studies. That is, does this population of people who for whatever reason eat more nitrites/nitrates have a higher incidence of cancer than the people that don’t? On one hand, this is an efficient and ethical way to do science because all you have to do is observe people living their life and see what happens. On the other hand there are loads of confounding variables that make interpreting this data difficult:  

• Are the people who eat more nitrates/nitrites more likely to work in industries where they are exposed to occupational carcinogens? 
• Are they more likely to have unbalanced diets? 
• Are they receiving poorer healthcare? 
• Are they more exposed to carcinogenic infections such as Helicobacter pylori? 
• Are they more likely to indulge in tobacco or excessive alcohol use?

Given the long list of confounding variables, it will not surprise you to learn that the results of the nitrite/nitrate epidemiological studies are all over the place. 

The experiments performed with lab animals are equally confusing. There is a long list of experiments where rats are dosed with nitrites in their food or drinking water. Focusing on just one study, there was no evidence of carcinogenic activity in male rats, there was a trend for female rats to develop carcinomas in their forestomach (put the body atlas down, you don’t have a forestomach) and there was evidence that the sodium nitrite used might prevent leukemia in both male and female rats.

And that, my friends, is how you bamboozle people with cancer research.

Originally published in Countrywide Magazine. Image by Emily Rees.