Carcinogens (and how to avoid them)
• Carcinogens are cancer-causing compounds, exposures to them are part of everyday life
• Many of these compounds exert their carcinogenic effect by damaging DNA, the code for life, or the structures and processes that surround the DNA
• Some carcinogens are difficult to avoid, such as vehicular emissions and occupational exposures
• Lifestyle exposures that can be reduced include excess UV exposure and smoking
• Alcohol is also potentially a carcinogen, specifically linked to several different cancers
• Dietary carcinogens include compounds that contaminate foods, notably fungal toxins from mouldy peanuts and grains, and toxic metals from some seafood and contaminated water supplies
• Highly potent dietary carcinogens include compounds that develop in red meat due to smoking, curing, burning and other processes.
• Other dietary carcinogens may include compounds from commercially baked goods but their significance undetermined
• Protection against dietary carcinogens can include a plant-based diet that provides fibre to help support bowel function to eliminate carcinogens
• A broad variety of vegetables and fruit also provide a range of protective phytonutrients that can help the body defend itself against carcinogens, and support general health.
In this article, we’ll look at some of the potentially avoidable substances that can trigger a normal cell to become a cancer cell. We’ll look particularly at cancer-causing substances in food and beverages, and in other lifestyle exposures, that can be reduced or avoided. These carcinogens include toxic metals, acrylamides, nitrosamines, heterocyclic amines and mycotoxins. We’ll look at how they can be potentially reduced by choices in food purchase, storage and preparation, and how their cancer-related effects may be reduced by other diet and lifestyle choices.
Carcinogens are substances that may cause cancer, by inducing normal cells to become malignant1. They contribute to cancer risk, and in this article, we’re going to look specifically at carcinogens that are linked to food, diet and lifestyle. Many carcinogens in food are potentially modifiable cancer risks2 and so it’s worth thinking about how you can reduce or avoid them if you’re fighting cancer or trying to reduce the chance of developing cancer.
Learn more about how food can impact cancerSee our video course for more detail
Carcinogens are everywhere
Modern life can be pretty toxic! Vehicle fumes, ultraviolet (UV) radiation, pollution, some workplace hazards, and some of the food and drinks we choose, all present the body with challenges. At the same time, living creatures have evolved some robust mechanisms for dealing with these challenges. That’s how we can have a glass of wine, and the effects are short lived, because we break down and excrete the alcohol. We can do the same clever process of detoxification with lots of other toxins, and our bodies don’t suffer long term effects. We have a set of processes provided by the liver, kidneys, bowel, lungs and skin, to excrete undesirable substances and prevent them doing damage. Just being alive, just breathing, expose us to carcinogens, so we do have strong defences against many carcinogens and other types of toxins3.
Some compounds however, have a deeply damaging effect on cells and we can’t always remove them, or undo the damage they cause. Let’s look first at the different ways that carcinogens in general, and some specific ones in the diet, may lead to cancer. To set the stage, we’ll examine a few biological processes that are commonly affected by carcinogens that can lead to the development of cancer.
DNA – the code for life
Each cell carries a biological codebook, DNA, an intricate structure of paired strands. This codebook is our genetic blueprint, which defines and governs the structure and function of every cell. The structure of the DNA, and the processes involving DNA, called replication and translation, can be affected by carcinogens. Since every single function of the cell is governed by instructions coded in the DNA, this damage can change the behaviour of the cell and potentially lead to cancer.
When a cell divides, as part of renewal, repair or growth, it must first copy (replicate) the DNA and then separate the two copies, and send each one into one of the two daughter cells. The code within the DNA is read or ‘translated’ to govern all cell processes. These processes of DNA replication and translation are carefully controlled, but they are susceptible to error, and the DNA material itself is susceptible to damage. This is how some carcinogens cause cancer. They can damage the DNA and corrupt the message, so that the cell behaves differently1-3. Some carcinogens cause breaks or abnormal bonds in the DNA, causing deformed arrangements in the DNA strands, so that the DNA doesn’t replicate properly, or doesn’t produce the correct message. Fortunately the body has a whole suite of repair mechanisms that can fix these mistakes in the DNA, because mistakes in DNA are surprisingly common, especially as we age. This is one reason why cancer becomes more common as we age. However, if the amount of damage exceeds the repair systems, then normal cells will be at greater risk of transforming to cancer cells.
An avoidable example of a DNA-damaging carcinogen, which leads to cancer, is benzopyrene, which is found in cigarette smoke3. It breaks both strands of the DNA in some of the cells in lung, the mouth and many other tissues. These ‘double-stranded breaks’ are difficult to fix. As cells are exposed to more benzopyrene, as well as a host of other carcinogens in cigarette smoke, they get more breaks in the DNA. The code in the DNA becomes corrupted, and the cell has an ever-increasing chance of producing a cancer.
Another carcinogen that damages DNA is UV light, especially some wavelengths. In sunburned skin, the DNA is damaged by UV light, increasing the risk of skin cancers – as well as accelerating ageing. So regular tanning in your teens will also mean more and deeper wrinkles as you age! Studies show a strong link between sunburn and malignant melanoma, an aggressive form of skin cancer4.5. On the other hand, moderate exposure to the sun allows you to make some vitamin D, which is important for immunity against cancer, and is vital for bone health6. Thus, aim for a balance – some sun is good for you, but too much over time can result in significant DNA mutations.
Some toxic metals in the environment and in foods and beverages, are toxins with a short term effect, and increase cancer risk with longer term exposure. Cadmium and arsenic are toxins, and carcinogens. Cadmium causes lung inflammation, as well as increasing cancer risk. As we will see, toxic metals can occur in sea water and in water supplies, and so enter the food chain.
Some carcinogens don’t directly damage the DNA, but they affect the structures and systems around the DNA that manage the way it is copied and translated, and increase the chances of a healthy cell becoming a cancer cell. These ‘epigenetic’ factors and processes can be disrupted by some carcinogens in food2. Thankfully, many of the protective foods that can fight cancer act to repair some of the damage at the epigenetic level that are caused by carcinogens7-9. See our article on Foods that Fight Cancer for more information.
Having seen how carcinogens may trigger cells to become cancerous, let’s take a look in more detail at some of the major carcinogens that are in the diet, and how they might be reduced or avoided.
"Eating vegetables helps to remove carcinogens from the body"
Carcinogens inherent in food and beverages
Some foods and beverages contain compounds that may be carcinogenic, regardless of how the food is handled, they’re intrinsic components of the food or beverage. Alcohol, as a widely enjoyed beverage, does unfortunately affect DNA through epigenetic abnormalities. It also indirectly affects the DNA because it can reduce the amount of folate, an important B-vitamin that is vital for DNA integrity. Folate is an essential component of normal epigenetic control of the DNA. Alcohol is recognised as a carcinogen linked to several cancers5, including cancer of the mouth, the oesophagus, stomach, liver, pancreas and breast. Research linking alcohol consumption with cancer seems to indicate that a very moderate intake of one or two units may be safe for some, but especially to have many days without alcohol each week.
Red meat, from beef, lamb, pork and other mammals are classed as ‘probable carcinogens’ because the evidence is still not completely convincing that they are foods that do cause cancer. Studies from very large numbers of people do highlight a link between red meat consumption, and cancers of the digestive system4,5. Some studies of meat and cancer risk haven’t been clear on the types of meats consumed, or the quality. However, as shall see in the next section, the ways that red meats are processed or cooked can dramatically increase the carcinogen load.
Carcinogens that can develop in foods
In this section, we’ll look at cancer-causing compounds can arise in foods during storage, processing and cooking. These carcinogens can be controlled to some extent, by choice of foods and how they are handled in the home. Of course when you eat outside the home, or buy prepared foods you have less control over these areas of risk. However, having this information enables people concerned about cancer to make balanced choices, because enjoying food is also important!
Love mushrooms, hate mould
In storage, foods can become mouldy. This is a problem that may start with food producers, and particularly mouldy nuts and grains can harbour mycotoxins, natural carcinogens produced by fungi 10. One of the most potent mycotoxins linked to liver cancer is aflatoxin, which is well recognised in the peanut farming and processing industry. Aflatoxin is produced by the mould Aspergillus flavus growing on peanuts, often invisibly, and it can develop during storage and stay on the peanut, even leading to contaminated peanut butter. Thankfully, there are rules in many countries requiring testing for aflatoxin in peanuts and other susceptible foods. So buying a reputable brand from a region with high standards of agricultural control is one way to reduce your risk of cancer linked to mycotoxin exposure. Other nuts and seeds and oils derived from them, and many grains are at risk of mycotoxins. Coffee and many grains and nuts, and products made from them, can be contaminated by another mycotoxin Ochratoxin11, which is classed as a probable carcinogen. Avoiding mouldy foods, buying fresh produce and using it promptly, can all reduce your risks of exposure to these potential cancer causing compounds in food. Although many types of moulds can be carcinogenic, not all fungi are. Mushrooms, on the other hand, are a healthy food that may help to support a healthy immune response, for more information see our ‘Foods that Fight Cancer’ article.
Processed and burned meat12
We’ve already seen that red meat is a probable carcinogen, and unfortunately meat can acquire some more potent carcinogens in processing. These develop due to a chemical reaction affecting animal proteins, so the cancer risk with these compounds is with protein foods such as meat and poultry, and fish to a lesser extent.
Curing meat using salt and nitrite (‘saltpetre’ or ‘pink salt’) produces nitrosamines, which are carcinogens that are also produced in cigarette smoke and can be found in water supplies. As well as this risk from nitrosamines, smoking meat and high temperature cooking produce heterocyclic amines (HCA), which are also potent food-derived carcinogens. They have been linked to several cancers notably stomach and bowel cancer, and also breast cancer. HCAs are produced when meat is burned, such as produced on a broiler or char-grill and especially a barbeque, which may also allow smoke from the coals to permeate the meat.
You can take steps to reduce your intake of these carcinogens, which are especially prevalent in processed and charred meats. You can choose unsmoked fresh meat or poultry, rather than cured or smoked. Secondly, cooking at lower temperatures, and using liquids in the cooking process, can protect meat from burning. A delicious chicken casserole, or braised lamb, for example, allow you to enjoy these high protein foods, and you can add veggies to the dish and boost your cancer-fighting foods at the same time. If you’re hosting a summer barbeque, a healthful option is whole fish in foil with a few herbs, which cooks well on a barbeque, and serve with along with salads and some vegetable skewers. If you are choosing to broil or pan-fry meat, then cook to just golden, and avoid it becoming too brown.
Baked starchy foods13-15
Acrylamides are carcinogens produced in starchy foods due to the heat of the baking process. Commercially produced baked goods such as crackers, bread, crispbreads and pizza crusts have been found to have higher levels than ‘home-made’ versions. In one study, higher levels were found in potato-flour based products. Some of the commercially made gluten-free crackers had the highest acrylamide levels. Acrylamides are also found in French fries and potato chips.
However, eating wholegrains may be beneficial for you, and the fibre from wholegrains does reduce the risks of cancers of the digestive system. Wholegrain consumption may also be linked to a lower risk of other health conditions such as cardiovascular disease, compared with eating refined starchy foods. So a good tactic for reducing your intake of acrylamides is to reduce your consumption of commercially baked refined starch products, and instead opt for unrefined grains like oatmeal and whole barley. If you re following a gluten-free regime, then wholegrain buckwheat and rice can be healthful options.
Acrylamides are also found in coffee15, again due to the heat involved in roasting. There are other considerations of coffee, which may be linked to some protection against some cancers. See our article on Coffee and Cancer for more details. There are still some questions about the significance of acrylamides as food carcinogens, as they are considered to carry modest cancer risks, compared with meat-derived carcinogens such as HCAs.
Toxic metals and other environmental carcinogens
A study of rural and urban Canadians set out to assess the sources of common cancer risks especially toxic metals and environmental carcinogens in food and beverages17. Arsenic, lead and PCBs were common in the typical diets eaten. There was little difference between country-dwellers and city inhabitants for most carcinogens except arsenic, which was much higher in urban diets. Fish and rice had the highest levels of arsenic, and cheese samples had the highest levels of lead, of the various foods and beverages sampled. However, these were traces of carcinogens, and there was variation in the samples tests. A European study18 of heavy metals in seafood identified certain varieties were much higher in arsenic than others – mollusc shellfish which feed by filtering seawater, and bottom-dwelling flat fish (demersal fish) had more arsenic that free-swimming (pelagic) fish varieties. Other studies have identified high levels of contamination with mercury in fish, some reporting over half of fish sampled exceeded acceptable limits19. Fish and shellfish species sampled in US waters were tested for mercury and the highest levels were seen in the largest fish, with shark being frequently heavily contaminated20. On the other hand, eating fish can be a healthy choice, particularly if small free-swimming varieties of fish are chosen. Avoiding large predator fish like shark, tuna and swordfish can be a reasonable way to reduce mercury exposure from food. Molluscs and flatfish harvested from polluted sea areas (major shipping routes, for example) might be more of a risk of carrying arsenic.
Reducing your risks
We’ve seen how some cancer causing compounds in foods can be reduced, such as choosing unprocessed meat, and how cooking can also have an effect. Another part of the equation is helping your body to expel these carcinogens or neutralise their effects. Firstly our article ‘Foods that Fight Cancer’ details many foods that help your body to fight cancer. Also, our online course (Introduction to Cancer Self Help) contains good information about how to think about food after a cancer diagnosis. One of the most effective ways to reduce the impacts of cancer-causing compounds is to follow a predominantly plant-based diet which includes plenty of leafy vegetables and a broad range of brightly coloured vegetables. These have protective compounds and especially fiber, which can reduce your exposure to the carcinogens in meat, by speeding up their removal from the bowel. Thus, eating lots of vegetables with meat is a good way to potentially reduce the impact of carcinogens from the meat itself.
We’ve seen how some compounds in food and beverages are carcinogens. Some of these cancer-causing substances are intrinsic in the food itself, such as red meats. Some carcinogens arise during storage, processing and cooking, and many of these can be reduced by choices of foods and cooking. Mould on foods may present a specific risk of mycotoxins, and careful purchasing can reduce this risk. On balance, some carcinogens such as acrylamides may represent a modest cancer risk, but some are identified as potent carcinogens, particularly those in processed, and burned meats. Toxic metal carcinogens may be present in some foods, with shellfish highlighted as a potential source of arsenic. As well as reducing carcinogen intake, having a plant-based diet is linked to a lower risk of many cancers as it can provide many nutrients and fiber that can reduce the potential risks of some of these carcinogens. As we explain in our Introductory Course to Cancer Self Help, plant foods really are king when it comes to cancer, both in prevention and after diagnosis.