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A study published in Nature Communications looks at dietary patterns in women and the risk of colorectal cancer.
Dr David Nunan, Senior Research Fellow at the Centre for Evidence Based Medicine, University of Oxford, said:
“A new observational study has tracked women’s dietary intake of certain foods and nutrients from around 2001, following them for nearly 17 years to investigate links with colorectal cancer diagnoses. Using both standard and advanced statistical methods, the study found that consuming 300 milligrams of calcium daily (roughly a glass of milk) was associated with a 17% relative reduction in the “risk” of developing colorectal cancer.
“While the study boasts a large sample size and rigorous statistical analysis, it remains susceptible to the biases inherent in all observational research, such as selection bias, measurement errors, and confounding factors. These biases often inflate the estimated associations compared to controlled experiments.
Interpreting “Risk” in Context
“The study reports relative risk—a 17% reduction when comparing higher calcium intake (e.g., 345 mg/day) to lower intake (258 mg/day). However, absolute risk differences, which offer a clearer sense of individual impact, were not reported. According to evidence-based medicine principles, both relative and absolute risk should be disclosed to allow for informed judgment.
“To illustrate:
“In the UK, approximately 5% of women (1 in 20) are diagnosed with colorectal cancer annually.
“Using the 17% relative risk reduction figure from the study, if 100 women increased calcium intake to 345 mg/day, the number of diagnoses could drop from 5 to 4—a difference of 1 fewer cases per 100 women.
“However, this means 95 out of 100 women would remain unaffected by cancer regardless of their calcium intake. Reporting both absolute and relative risk helps contextualise these findings for practical decision-making.
Key Takeaways
“While this study highlights a potential benefit of increased dietary calcium, journalists and the public should approach the findings with caution. The reported figures may overstate the true effect due to methodological limitations. More robust research, such as randomised controlled trials, is needed to establish causation.
“For now, the study underscores the importance of understanding dietary risk factors but also the need to communicate risk in a way that is transparent and balanced.”
Prof Andrew Prentice, Theme Leader for Nutrition & Planetary Health at the MRC Unit The Gambia, London School of Hygiene & Tropical Medicine (LSHTM), said:
“This very impressive study of how diet can influence the risk of colon cancer showcases the value of mass participation in medical research for which the UK and NHS are becoming justly famous worldwide. With well over half a million women followed for an average of 16 years and with over 12,000 cases of colorectal cancer the researchers have confirmed that drinking alcohol and eating red and processed meats are associated with small increases in risk. This was well known already. They showed that many dietary habits are protective including eating plenty of fruits and vegetables, together with wholegrains and dietary fibre, again reinforcing previous knowledge.
“Their results emphasise that milk consumption is particularly beneficial and show evidence that this effect may be largely due to the calcium in milk, begging the question as to whether calcium supplements might be protective. The jury is out on this but as a nutritionist I shall continue to take my calcium from milk and dairy foods which are rich in so many nutrients.”
Prof Janet Cade, Professor of Nutritional Epidemiology and Public Health, University of Leeds, said:
“This well conducted analysis of a large group of women in the UK takes account of dietary patterns using a diet-wide association study. This allowed for 97 different dietary factors in relation to risk of colorectal cancer to be identified. Whilst calcium, represented largely by milk, reduced risk this was not the only association. Alcohol intake had a similarly strong association to calcium but in the other direction, increasing risk. Alcohol intake and milk consumption are relatively easy to assess clearly using self-reported methods. Other dietary factors were also linked to risk of colorectal cancer: with red and processed meat increasing intakes and breakfast cereal, fruit, wholegrains, carbohydrates, fibre, total sugars, folate, and vitamin C reducing risk. The authors suggest that these weaker associations might be affected by other lifestyle or dietary factors confounding the associations. Alternatively, the associations might be weaker because these components of the diet are more challenging to assess and may have more measurement error as a result of using questionnaire data. This paper provides important evidence showing that overall diet can influence risk of colorectal cancer.”
Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London (KCL), said:
“This is a very large observational study of risk of colorectal cancer in British women. Its strength is the large sample size, length of follow up (542,778 participants with 12,251 incident cases over 16.6 years), and good statistical analysis. The study confirmed the positive relation with alcohol intake (20 g alcohol/day) which increased risk by 15%). The main finding about diet was that a 300 mg higher intake of calcium per day was associated with a 17% lower risk of colorectal cancer. Cows’ milk is a rich source of dietary calcium and riboflavin and the relationships between milk, calcium and riboflavin and risk of cancer incidence were almost identical. A weaker protective relationship was found with breakfast cereals, especially wholegrain cereals but this could be confounded by the fact that breakfasts are consumed with milk. Calcium intake has previously been found in other studies to be linked to a lower risk of colorectal cancer. One theory is that the calcium may bind to free bile acids in the gut preventing the harmful effects of free bile acids on gut mucosa.
“The limitations of the study are that it is observational and not a randomized controlled trial. It is also difficult to separate the effects of individual nutrients from an effect of milk per se. Milk also has effects on the large bowel microflora due to its lactose content which may in turn affect risk.
“In my opinion, the take home messages of this paper are that drinking above the safe limits of alcohol intake (more than 14 units/week) increases risk of colorectal cancer in women but that drinking about half a pint of cows‘ milk a day (which would provide about 300 mg calcium) is probably protective.”
Professor Ian Givens, a professor of food chain nutrition and also director of the Institute of Food, Nutrition and Health at the University of Reading, said:
“This major study of over half a million UK women provides compelling evidence that dairy consumption, particularly milk and yoghurt, is linked to reduced colorectal cancer (CRC) risk with the calcium in milk being a likely driver. The findings align with previous research and notably used genetic markers of milk consumption to strengthen the conclusions. What’s particularly concerning is that many UK women, especially younger age groups, are consuming less dairy and have calcium intakes below recommended levels.
“While we’ve long known calcium’s importance for bone health, this study suggests inadequate intake may also impact cancer risk. The protective effect appears to be driven by calcium and magnesium – nutrients that dairy foods are particularly rich in. Combined with other large-scale research, these findings make a strong case for maintaining adequate dairy consumption as part of a balanced diet.
“The study also showed that consumption of red/processed meat and especially alcohol were associated with increased risks of CRC, again in agreement with earlier World Cancer Research Fund/American Institute for Cancer Research findings. Until recently the association of alcohol and cancer has had little publicity, but clearly this needs to continue.”
Dr Lisa Wilde, Director of Research and External Affairs at Bowel Cancer UK, says:
“Every twelve minutes, someone in the UK is diagnosed with bowel cancer, making it the fourth most common cancer in the country. We already know that around half of all bowel cancers could be prevented by having a healthier lifestyle and this new research supports this, with a particular focus on dairy.
“This study shows that drinking dairy milk is associated with a reduced bowel cancer risk. If you don’t drink dairy milk there are other ways you can get calcium, for example from broccoli or tofu, and still reduce your bowel cancer risk.
“Other changes you can make to help reduce your risk of developing bowel cancer include eating plenty of fibre from wholegrains, pulses, fruits, and vegetables, avoiding processed meat and limiting red meat, being a healthy body weight, taking part in regular physical activity, stopping smoking and cutting down on alcohol. Making lifestyle changes can be a challenge, but we believe it’s worth the effort.”
‘Diet-wide analyses for risk of colorectal cancer: prospective study of 12,251 incident cases among 542,778 women in the UK’ by Keren Papier et al. was published in Nature Communications at 10:00am UK time Wednesday 8 January 2025.
DOI: 10.1038/s41467-024-55219-5
Declared interests
Prof Ian Givens: I have received travel expenses and honoraria in connection with lectures and meetings from the Dairy Council (now Dairy UK), Dutch Dairy Association, European Milk Forum, and the International Dairy Federation. I have also been a consultant to BioCC OÜ the Estonian Bio-Competence Centre of Healthy Dairy Products, to the Dairy Council (now Dairy UK) on fats in dairy products and cardiometabolic diseases and to the School and Nursery Milk Alliance on research evidence on the role of milk in the diets of infants and children.
Prof Tom Sanders: “Member of the Science Committee British Nutrition Foundation. Honorary Nutritional Director HEART UK.
Before my retirement from King’s College London in 2014, I acted as a consultant to many companies and organisations involved in the manufacture of what are now designated ultraprocessed foods.
I used to be a consultant to the Breakfast Cereals Advisory Board of the Food and Drink Federation.
I used to be a consultant for aspartame more than a decade ago.
When I was doing research at King’ College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks. In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.”
Prof Janet Cade: “I am an employee of the University of Leeds.
I am Director and shareholder of Dietary Assessment Ltd., a spinout company from the University of Leeds, which has produced a software tool for dietary assessment called myfood24.
I chair the Advisory Committee of the British Nutrition Foundation: https://www.nutrition.org.uk/our-work/who-we-are/committees/advisory-committee
I receive no financial remuneration for doing that role. (BNF weblink: https://www.nutrition.org.uk/our-work/who-we-work-with/).
I lead a WHO Collaborating Centre in Nutritional Epidemiology.”
Prof Andrew Prentice: I sit on the General Nutrition Science Council for the Nestlé Nutrition Institute. NNI is a charitable medical education foundation focused of infant and child nutrition.
For all other experts, no reply to our request for DOIs was received.