The sugar in soda and fruit juice may increase risk of cancer, study warns

11 Jul 2019 --- Sugary drinks – including fruit juice and soda – may increase the overall risk of cancer, a study published in the British Medical Journal (BMJ) has found. While sugary drinks have already been indirectly linked to cancer through obesity, the researchers suggest this connection could also be due to other factors – such as increased blood sugar or visceral fat levels. The French-based study is the first significant research to establish a specific association between sugar and cancer, but the researchers posit that further work is warranted to cement sugary drinks as a modifiable cancer risk.

In a context where the World Health Organization (WHO) is questioning the level of evidence supporting the implementation of a tax on sugary drinks, the results of this observational study are extremely significant. Also in the UK, Boris Johnson, who is vying to become the nation’s next Prime Minister, recently promised a review of “unhealthy food taxes,” or so-called “sin taxes,” as part of a government examination of whether levies on foods high in salt, fat and sugar are effective.

Sugary drinks – including fruit juice and soda – may increase the overall risk of cancer.“The deleterious impact of sugary drinks on cardio-metabolic health is well established. Sugary drinks are convincingly associated with the risk of obesity, which in turn, is recognized as a strong risk factor for many cancer sites,” Eloi Chazelas and Dr. Mathilde Touvier, Head of the EREN team and Principle Investigator of the NutriNet-Santé cohort, tells NutritionInsight.

“Analyses of this study suggest that being overweight and weight gain may not be the only drivers of the association between sugary drinks and cancer risk, but that the relationship observed was also strongly driven by its sugar content. Thus, the main results of this study were not surprising, even though these associations were less expected for 100 percent fruit juices,” they add.

How significant a risk?
Overall, 101,257 participants aged 18 and over from the French NutriNet-Santé cohort (2009-2017) were included. Consumption of sugary drinks and artificially sweetened beverages were assessed by using repeated 24-hour dietary records.

The mean daily intake of sugary drinks across all participants was about 93ml, and the findings suggest that a 100ml daily intake – about two cans a week – of sugary drinks increases the risk of developing some form of cancer by 18 percent. A 30 percent increase in “all cancer” diagnosis was noted in those with the highest intake of sugary drinks when compared to those in with the lowest consumption. 

Commenting on the study, Dr. Graham Wheeler, Senior Statistician, Cancer Research UK & UCL Cancer Trials Centre, says: “This large, well-designed study adds to the existing evidence that consumption of sugary drinks may be associated with increased risk of some cancers.”These data support the relevance of existing nutritional recommendations to limit sugary drinks consumption, say the researchers.

“However, if we assume that a real causal link between consumption of sugary drinks and cancer does exist, then we can speculate with the authors that the mechanism may be related to an increased risk of obesity, which is a well-established risk factor for various types of cancer, or perhaps to the frequent spikes in blood sugar levels that may be associated with habitual consumption of such drinks,” adds Dr. Ian Johnson, Nutrition researcher and Emeritus Fellow, Quadram Institute Bioscience, who also commented on the study.

Indeed, the study does not present a causal relationship between cancer and sugary drink consumption, but it does show that those who drink more sugary beverages have more cases of cancer. 

There could be other mechanisms at play here. The researchers note that the association may be partly explained by sugary drinks’ link with obesity – which is known to cause cancer. More specifically, it has been suggested that sugary drinks might promote gains in visceral adiposity independently of body weight, which may play a role in the association with cancer. A further pathway could be the high glycemic index of sugary drinks, which previous studies have pinpointed to be a cancer risk factor.

The association may be partly explained by sugary drinks’ link with obesity.Obesity’s link with cancer was further documented in recent Cancer Research UK findings, which showed that excess weight causes more cases of certain cancers than smoking, and that people who are obese now outnumber people who smoke two to one in the UK. 

How can the industry use these findings?
Speaking to NutritionInsight, the researchers note that the food industry might use these findings by reducing the sugar content of their beverages, without replacing sugar with artificial sweeteners. Public health authorities in France already encourage limiting sugary drink intake (less than one small glass per day), while the UK has had a sugary drink tax, the “Soft Drinks Industry Levy,” in place since April 2018. 

“These data support the relevance of existing nutritional recommendations to limit sugary drinks consumption, including 100 percent fruit juices, as well as policy actions such as taxation and marketing restrictions targeting sugary drinks, which might potentially contribute to the reduction of cancer incidence,” they say.

These results essentially open new perspectives for cancer prevention. In terms of research, the challenge is now to establish a causal link, note the researchers. The strategy will be to replicate these findings in other large-scale prospective studies to further extrapolate the mechanisms behind the link. If they can be replicated, these beverages will represent a modifiable risk factor for cancer prevention beyond their well-established impact on cardiometabolic health. 

By Laxmi Haigh