Consumption of two sweetened drinks during teenage doubles bowel cancer risk later

And each daily serving is associated with a 16% higher risk, rising to 32% per daily serving during the teenage years, the findings indicate.

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.

In the US, adults born around 1990 run twice the risk of colon cancer and four times the risk of rectal cancer of adults born around 1950.

Sugar-sweetened beverages, such as soft drinks, fruit flavoured drinks, sports and energy drinks, make up the leading (39%) source of added sugar in US diets, and 12% of the population drinks more than three servings (8 fl oz each) every day.

Heavy consumption has been linked to a heightened risk of obesity and type 2 diabetes. Although these drinks have steadily risen in popularity, particularly among teens and young adults, it's not known if this intake might also be associated with a heightened risk of bowel cancer in mid-life.

To explore this further, the researchers drew on information provided by 95,464 participants in the Nurses' Health Study II, an ongoing monitoring study of 116,429 US female registered nurses aged between 25 and 42 at enrolment in 1989.

The women reported what they ate and drank, using validated food frequency questionnaires every 4 years, starting in 1991. And 41,272 of them reported on what, and how much, they drank during their teenage years (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.

In 1989, participants were additionally asked to recall their health status, weight (BMI) and lifestyle in their teenage years.

During 24 years of monitoring, 109 women developed bowel cancer before the age of 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 2 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.

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

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

These drinks also prompt a rapid rise in blood glucose and insulin secretion, which, over the long term, can induce insulin resistance, inflammation, obesity and type 2 diabetes, they add.

Emerging evidence also suggests that fructose can impair gut barrier function and increase gut permeability, which could promote the development of cancer, suggest the researchers.

"[Sugar-sweetened beverage] consumption may contribute to the rising incidence of [early onset bowel cancer]," they suggest.

"Reducing intake and/or [substitution] with other healthier beverages among adolescents and young adults may serve as a potential actionable strategy to alleviate the growing burden of bowel cancer before the age of 50]," they conclude.