Why a daily glass of milk really could reduce bowel cancer risk – an oncologist explains

A glass of milk a day could help keep bowel cancer away – or so finds a study by Oxford University and Cancer Research UK. The research suggests that increasing daily milk intake by as little as one glass could have a significant impact on lowering the likelihood of developing bowel cancer.

There are nearly 45,000 cases of bowel cancer every year in the UK, making it the nation’s fourth most common cancer – and third worldwide – but many of these are preventable. According to Cancer Research UK data, 54% of all bowel cancers could be prevented by having a healthier lifestyle. Smoking, lack of exercise, alcohol, eating processed meat, and poor diet are all significant factors in the development of bowel cancer.

Read more: King Charles is changing his diet to keep his cancer at bay – here's what the evidence says

As an oncologist, I advise my patients about how diet and lifestyle can influence health, including the risk of developing cancer. But this research – one of the largest studies into diet and disease so far – has shed new light on how easy, cheap diet changes can help everyone to reduce their cancer risk.

For example, as well as drinking an extra glass of milk per day, reducing consumption of alcohol and red and processed meat could also help protect against cancer. The study found that drinking an additional 20g of alcohol a day, equivalent to a large glass of wine, increased bowel cancer risk by 15%. Consuming more than 30g of red and processed meat daily was linked to an 8% increase in bowel cancer risk.

Read more: The role alcohol plays in new cancer cases – landmark new report

Researchers took a novel, two-pronged approach to examine the association between milk consumption and bowel cancer risk. First, they analysed genetic data from over 542,000 women and focused on variants – tiny changes in DNA – associated with lactase persistence, the ability to digest lactose in adulthood.

Second, the team collected detailed dietary information from participants, including their daily milk intake. By combining these two data sets, the researchers were able to better estimate the causal effect of milk consumption on bowel cancer risk.

Striking results

The analysis revealed that participants who consumed an additional 244g of milk per day – roughly equivalent to one large glass containing 300mg of calcium – had a 17% lower risk of developing bowel cancer. This reduction in risk applied to various types of milk, including whole, semi-skimmed and skimmed.

Researchers found that the protective effect of milk consumption was independent of other dietary factors and lifestyle habits. This suggests that the benefits of milk in reducing bowel cancer risk are not because milk replaces unhealthy food choices or is consumed as part of an overall healthier lifestyle.

The reasons why milk consumption may reduce bowel cancer risk are not fully understood, but the researchers propose several potential explanations. First, milk is a rich source of calcium, which has been linked previously to a reduced risk of bowel cancer. Calcium may help protect against cancer by binding to potentially harmful substances in the gut and promoting the death of abnormal cells.

Next, many milk products are fortified with vitamin D, which has been shown to have anti-cancer properties and may help regulate cell growth and division. Also, the lactose in milk can promote the growth of beneficial gut bacteria that produce butyrate, a short-chain fatty acid with anti-inflammatory and anti-cancer effects. Finally, milk contains conjugated linoleic acid, a fatty acid found in meat and dairy products, which, according to a 2021 labratory study, could also have anti-cancer properties.

Crucially, milk consumption may not be suitable or beneficial for everyone. Those with lactose intolerance, milk allergies, or other dietary restrictions should consult with healthcare professionals before making significant changes to their dairy intake.

Overall, this groundbreaking research provides compelling evidence for the potential role of milk consumption in reducing bowel cancer risk. The finding that a relatively modest increase in daily milk consumption could lead to a significant reduction in bowel cancer risk is particularly encouraging. It suggests that small, achievable changes in diet could have meaningful impacts on public health.

As we continue to unravel the complex relationships between diet and disease, studies like this one provide valuable insights that can inform both individual health choices and broader public health strategies. The potential for a simple dietary change to have such a significant impact on cancer risk underscores the importance of continued research in this field and highlights the power of nutrition in shaping our health.

Justin Stebbing does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.