Drinking two or more sugary beverages a day could double your risk of bowel cancer before the age of 50 – at least in women.

New research, published in the journal Gut, found each daily serving of sugary drinks is associated with a 16% higher risk of the cancer, and 32% for teens.

Cases of bowel cancer diagnosed before the age of 50, formally known as early onset colorectal cancer, have been increasing in many high income countries over the past two decades. But it’s not clear why.

Sugar-sweetened beverages, such as soft drinks, fruit flavoured drinks, and sports and energy drinks, have previously been linked to a heightened risk of obesity and type 2 diabetes. 

To explore this further, researchers drew on information provided by 95,464 participants in the Nurses’ Health Study II, a monitoring study of US female registered nurses aged between 25 and 42 in 1989.

The women reported what they ate and drank, using food questionnaires every four years, starting in 1991. And 41,272 of them reported on what, and how much, they drank during their teenage years (aged 13–18) in 1998. 

Information was also supplied on potentially influential factors, including family history of bowel cancer, lifestyle, regular use of aspirin or non-steroidal anti-inflammatory drugs and vitamin supplements.

What did the study find?

During 24 years of monitoring, 109 women developed bowel cancer before age 50. Higher intake of sugar-sweetened drinks in adulthood was associated with a higher risk of the disease, after accounting for potentially influential risk factors. 

Compared with those who drank less than one serving a week, women who drank two or more every day were more than twice as likely to be diagnosed with bowel cancer, with each daily serving associated with a 16% higher risk.

Among the 41,272 who reported on their teen patterns of consumption, each daily serving was associated with a 32% higher risk of subsequently developing the disease before the age of 50.

Substituting sugar-sweetened drinks with artificially sweetened beverages, coffee, or semi-skimmed or whole milk was associated with a 17% to 36% lower risk of a bowel cancer diagnosis before the age of 50.

Why do sugary drinks increase the risk of cancer?

This is an observational study, and as such, can’t establish cause. And given that most participants were white women, the findings may not be applicable to men or those in other racial/ethnic groups, the researchers acknowledge.

Nevertheless, they point out that there are some biologically plausible explanations for their findings: sugar-sweetened drinks suppress feelings of satiety [feeling full], risking excess energy intake and associated weight gain.

These drinks also prompt a rapid rise in blood glucose and insulin secretion, which, over time, can induce insulin resistance, inflammation, obesity and type 2 diabetes, the researchers said, citing emerging evidence that also suggests fructose can impair gut barrier function and increase gut permeability, which could promote the development of cancer.

Reducing intake of sweetened drinks or substituting healthier beverages among teens and young adults could alleviate the growing burden of bowel cancer before the age of 50, they conclude.