There are often stories in the media about certain foods or nutrients that are supposed to increase or decrease the risk of cancer. On the balance of evidence, it's unlikely that specific 'superfoods', on their own, could directly affect the risk of cancer, but some of the stories are still controversial.
Explore some of the stories you may have read or heard about, and find out our take on the evidence.
Acrylamide is produced from cooking starchy foods at high temperatures (e.g. baking and frying) and is found in foods such as biscuits, coffee, bread, and fried potato products (like crisps and chips).
Evidence from animal studies shows that acrylamide has the potential to interact with the DNA in our cells, so could be linked to cancer. However, evidence from human studies has shown that, for most cancer types, there is no link between acrylamide and cancer risk. Some studies have suggested a higher risk of womb cancer, but the evidence is weak and inconsistent, so we can’t be sure if this link is real. Even food industry workers, who are exposed to twice as much acrylamide as other people, do not have higher rates of cancer.
Experts at the European Food Standards Agency have concluded that because we don’t know how much acrylamide people are exposed to, they can’t draw any definite conclusions about any cancer risk from acrylamide in our food. At the moment, there is no strong evidence linking acrylamide and cancer.
Artificial sweeteners are used in a wide variety of foods and drinks. While there have previously been questions over their safety after early animal studies, large studies in humans have provided strong evidence that artificial sweeteners do not increase the risk of cancer.
The most extensively studied artificial sweeteners are saccharin and aspartame.
Saccharin was the subject of a cancer scare after studies in the 1980s found that it could cause bladder cancer in rats. We now know that these effects were specific to rats and not relevant to humans. However, because this was not known at the time, the Canadian government banned saccharin, and the American government warned that it could cause cancer. Studies in humans have found no link between saccharin and bladder cancer.
People were also worried about aspartame in the mid-1990s and in 2006. In the mid-1990s an article linked the artificial sweeter to rising brain cancer rates, however, this article had very little scientific basis and many later studies showed that aspartame was safe for humans. In 2006, another study in rats suggested a link to cancer but the European Food Safety Authority (EFSA) found that the study had some major flaws and concluded that aspartame does not increase the risk of cancer below the daily recommended level. Even people who consume a lot of sweetened foods take in well below this amount.
Large studies looking at humans have now provided strong evidence that artificial sweeteners do not increase the risk of cancer. For example, one study looked at almost half a million people and found that aspartame does not increase the risk of leukaemia, lymphoma or brain cancer.
All sweeteners are tightly regulated and rigorously tested for safety by the European Food Standards Agency. There is no strong evidence that sweeteners are linked to cancer risk.
Green tea and cancer risk has been extensively studied. Results from large human studies have shown no strong evidence that green tea could reduce the risk of pancreatic, lung, breast, prostate, stomach, bowel, thyroid, liver, endometrial, laryngeal, bladder, oral, ovarian, kidney, or oesophageal cancers.
Green tea contains a high amount of a group of chemicals called catechins. Green tea has higher levels of catechins than black tea.
While laboratory studies have found that catechins could block the growth of cancer cells, and stop cancer-causing chemicals being activated, human studies have not shown any strong evidence linking green tea and cancer risk.
Milk and dairy are good sources of calcium and protein which are needed as part of a healthy, balanced diet. Calcium is important for teeth and bone health.
Studies looking into the link between cancer and dairy products have not given clear results. There is evidence that dairy products could reduce the risk of bowel cancer, but we cannot say for sure that this is the case. There is no strong evidence linking dairy products to any other types of cancer. We need further research to find out more about the links between dairy products and cancer risk.
Hormones in milk
In some countries, a hormone called bovine somatotrophin (BST) is used to speed up or increase the production of milk or meat. In the UK and the rest of Europe, farmers are banned from using this hormone, and the import of meat from countries, including the US, where this hormone is used is also banned. This ban is on animal welfare grounds and not because there is any proven effect on human health. Independent health bodies including the European Union Scientific Committee have reviewed the evidence on BST and found it does not pose any harm to human health.
The Food Standards Agency regulates the content of dairy products, including milk. This set of standards makes sure these products are safe to use.
Pesticides are widely used in agriculture. High doses of some pesticides can cause cancer in animals, but the levels found in foods are tightly regulated to make sure they are well below this dose. The Food Standards Agency is responsible for food safety and standards in the UK. The Agency considers that current levels of pesticide residues in the UK food supply does not present a significant concern for human health.
Fruit and vegetables sometimes contain very small amounts of pesticides on the surface. But there is no evidence that these small amounts increase the risk of cancer in people who eat them. There is also evidence that eating organic food – which doesn’t use pesticides - doesn’t affect cancer risk.
In fact, fruit and vegetables are an important part of a balanced diet, providing vitamins, minerals and fibre - and people who eat plenty of fruit and vegetables may have a slightly lower cancer risk.
Agricultural workers and farmers
There is some evidence that people exposed to higher levels of pesticides as part of their job, for example in industry or through farming, may be at slightly higher risk of cancer.
The International Agency for Research into Cancer (IARC) has looked at the evidence and said that regularly spraying pesticides as part of your job “probably” slightly increases the risk of cancer. But for most individual pesticides, the evidence was either too weak to come to a conclusion, or only strong enough to suggest a “possible” effect.
It can be hard to study pesticides as very few people are exposed to them in their day-to-day jobs, and it’s difficult to accurately measure how much someone has been exposed to.
To protect workers, and also the public, pesticide use is monitored and regulated on a global, European and UK level, by the World Health Organisation, the European Food Safety Agency and the Health and Safety Executive. These websites have information on how workers can make sure they are using these products as safely as possible.
Pesticides which research has clearly shown to be dangerous, such as DDT and lindane, have now been banned by regulatory agencies.
Glyphosate is a broad spectrum herbicide (weed killer). It is the main active ingredient in Roundup, and is widely used in agriculture as well as home gardening.
There is a small amount of evidence that people who are exposed to the highest levels of glyphosate may have a small increased risk of certain types of cancer. But there’s no good evidence that there’s an increase in risk for people exposed at low levels, such as through using glyphosate as a weed killer in their garden.
Soy (or soya) products such as tofu and soy milk are made from soybeans, and contain a group of chemicals called isoflavones. These isoflavones are plant-based oestrogens which have a similar structure to the human oestrogen, but with much milder effects. Laboratory studies have shown that these isoflavones can mimic the effects of oestrogen in our bodies, which scientists think could reduce the risk of some hormonal cancers.
However, the effect of soy in human studies is less clear. Some studies have shown that diets high in soy could reduce the risk of prostate cancer, but it’s not clear if this is really the case. There is no strong evidence for a link between soy and any other cancer type.
Many studies which look at the effect of soy on cancer risk take place in Asian countries, where generally people have more soy in their diets than in Western countries. This means that results may not be relevant to people in the UK.
More studies are needed to understand if there is a link between soy and cancer.
The term ‘superfood’ is used to describe foods with apparently special health-related powers. These often include blueberries, broccoli, raspberries, green tea and many more. Typically, such foods are hailed as having the power to prevent or even cure many diseases, including cancer.
But the term ‘superfood’ is really just a marketing tool, with little scientific basis. It’s certainly true that a healthy, balanced and varied diet can help to reduce the risk of cancer but it is unlikely that any single food will make a major difference on its own.
Many so-called ‘superfoods’ contain natural chemicals that have been shown to have positive health effects in laboratory studies. These include antioxidants, vitamins and minerals. It is true that some of these ingredients can affect cancer cells in a laboratory setting, including killing them and stopping them from growing. However, foods contain many chemicals and laboratory studies are usually carried out using a purified ingredient from a particular food. So if researchers want to test the effect of an antioxidant contained in blueberries, they will use a purified version of that chemical rather than fresh blueberries.
Our diets are made up of hundreds of different types of food with thousands of different nutrients. An isolated chemical may behave very differently in a test tube than when it is eaten as part of food.
For example, the dose may be different. Often, scientists have to use very large doses of these purified compounds to see any effects in their studies. Typically these doses are much higher than what we would actually get in our diet. So even eating very large portions of a ‘superfood’ might not provide enough of a specific ingredient to have any effect on our health.
Tomatoes contain a chemical called lycopene. Lycopene is an antioxidant, which can mop up free radicals that could damage DNA. Lycopene is found in all forms of tomatoes and tomato products including fresh, tinned, paste, juice and ketchup.
In human studies it’s unclear if lycopene can reduce the risk of prostate cancer. More research is needed to say for sure whether lycopene can affect cancer risk.
But even so, it’s important to remember that eating tomatoes still counts towards your five day. And they’re also an excellent source of vitamins A, C and E.
Vitamin supplements do not have the same benefits as getting naturally-occurring vitamins in your food. It is thought that in fruit and vegetables, vitamins and nutrients interact with other chemicals to produce positive effects. On their own, they could be much less beneficial.
Several clinical trials have looked at the effects of vitamin supplements on cancer risk. Some of these have found that very high doses could actually increase the risk of cancer. An organisation called the Cochrane Collaboration first carried out a review of the evidence in 2008, which was updated in 2012 and now includes the results of 78 clinical trials of vitamin supplements. It found that these supplements, far from prolonging a person's life, either have neutral or harmful effects.
The best way to get your full range of vitamins and minerals is to eat a healthy, balanced diet, with a variety of fruit and vegetables. Supplements do not substitute for a healthy diet, although some people may be advised to take them at certain times in their lives. For example, doctors may advise women who are planning to have a baby to take a daily 400-microgram supplement of folic acid.
Some groups of people, such as people aged under 5 or over 65, pregnant or breastfeeding women, those with darker skin, and those who are housebound or cover their skin for cultural reasons, are advised to take vitamin D supplements since they are at risk of low vitamin D levels. During the autumn and winter months, the government recommends everyone should consider taking vitamin D.