Judging by the headlines, you’d think there’s a laundry list of foods that cause or protect against cancer (or, in some cases, manage to do both at the same time). Discovering how certain foods are linked to cancer risk is a complex question, which Professor Tim Key has dedicated his career to answering.
When he first arrived at the Cancer Epidemiology Unit (CEU) at the University of Oxford, now part of the Nuffield Department of Population Health (NDPH), as a PhD student in the 1980s, Key didn’t know he would end up leading a cancer study. of epic proportions, studying the impact of diet, hormones and lifestyle on cancer risk.
Today he is professor of epidemiology, deputy director of the CEU and principal investigator of EPIC-Oxford – a study of around 65,000 people in the United Kingdom aimed at elucidating the complex relationships between lifestyle and health.
Science on an EPIC scale
The Oxford group is part of a much larger project known as EPIC (the European Prospective Survey on Cancer and Nutrition) which includes more than half a million participants recruited in ten European countries and followed for 20 years.
Launched in 1993, EPIC was the largest study of diet and health ever undertaken at the time, and it remains one of the largest prospective cohort studies in the world.
Participants were asked to complete detailed questionnaires about their diet and lifestyle, which are analyzed alongside medical records, physical measurements and more than 9 million biological samples such as blood cells and plasma . They will be followed in the future, until their death, to see if there is a link between their diet and their health.
Studying diet and disease risk is difficult because, unlike a specific behavior like smoking, everyone has to eat. People’s diets can vary widely and there can be multiple confounding factors such as genetics, geography and culture, as well as social inequalities.
Despite this, researchers working on EPIC have published hundreds of scientific articles detailing the results on all kinds of risk factors, with over 60 from the Oxford group alone.
Risk classification
Alcohol consumption and obesity emerge as important diet-related risk factors for several types of cancer. After that, the study shows that the risk of bowel cancer is higher in people who eat more processed meat or less fiber, and there is evidence that sticking to a “diet Traditional Mediterranean” is associated with reduced risk of heart disease and longer survival. the elderly. After that, the evidence becomes less clear.
“We initially expected to see big changes in cancer risk associated with specific foods, but in reality, that’s generally not the case,” says Key. “We don’t have definitive answers on topics such as fruit and vegetable consumption, sugar, dairy, vitamins and minerals.”
Professor Key highlights inconclusive, negative, and even potentially harmful results from clinical trials of various vitamins and minerals intended to prevent cancer. For example, studies investigating whether supplements of beta-carotene, a precursor to vitamin A, could reduce the risk of lung cancer in smokers. in fact, it had the opposite effect.while several trials testing whether the mineral selenium can reduce the risk of prostate cancer have been conducted. failed to show significant benefit.
‘Studies like this tell us that there is probably a very wide range of ‘OK’ levels for most of these substances,’ says Professor Key. “Very low levels are bad and very high levels can be bad, but there is a wide band in the middle where everything is fine.”
Faced with an ever-expanding multibillion-dollar supplement industry and celebrities promoting “wellness” diets containing all kinds of superfoods, large-scale studies and analyzes like those of Key and his NDPH colleagues are essential if we want to develop evidence-based recommendations. on foods and food supplements that really contribute to improving the health of the population.
The heart of the problem
Professor Key also wants to know whether following a vegetarian or vegan diet has health benefits or harms. EPIC-Oxford has a particular advantage here because it recruited many participants who had participated in an earlier study known as Oxford Vegetarian Study, which started in 1980.
Of the 65,000 people in the Oxford cohort, half do not eat meat. Some are vegetarians while others are pescatarians, eating fish and seafood but not other types of meat, and a smaller number are vegans. However, although Key found that the risk of heart disease is reduced by about a third in vegetariansThis does not appear to translate into longer lifespans for those who choose not to eat meat – a curious observation that requires further research.
Professor Key is also interested in the relationship between hormones and cancer risk, particularly sex hormones such as estrogens and insulin-like growth factors (IGFs). He collaborates with researchers working on Study on a million women, which primarily focused on the relationship between hormones and breast cancer risk, to examine dietary information collected from participants. He is also expanding his scope of work to include other important health conditions, including cardiovascular disease, stroke, arthritis, bone fractures, and diverticular (intestinal) disease.
‘The most important things we know that definitely reduce cancer risk may seem simple: firstly, not smoking, secondly being a healthy weight and not drinking too much alcohol,’ Professor Key points out. “Everyone wants the magical things from the headlines to come true: ‘eat turmeric and you won’t get cancer!’ » – but at the moment we have no proof.
Key and his team continue to systematically examine data from EPIC and other large cohort studies looking for relationships between disease, diet, and other factors.
Professor Key said: “Although many previously published results have been negative or inconclusive, particularly regarding the role of certain foods in cancer risk, this does not mean that we will not find more robust results In the coming years. , because having larger studies and data sets with high-quality measurements, supported by biomarkers, gives you a better chance of formulating a good question and finding the answers.
