Cancer Risk From Sugary Drinks?

Zosia Chustecka

July 11, 2019

Consumption of sugary drinks, including fruit juice, was positively associated with the overall risk for cancer and the risk for breast cancer in a large prospective study conducted in France.

Although the study is observational and so cannot establish causation, the researchers suggest that "sugary drinks, which are widely consumed in Western countries, might represent a modifiable risk factor for cancer prevention."

The research was published online on July 10 in the BMJ

Nutrition experts who reacted to the findings said the trial was well designed and agreed that it adds ammunition to public health policies, such as the imposing of taxes, that discourage the overconsumption of sugar-sweetened beverages.

One expert, however, questioned some of the results and said the main message from the study should be the fact that the consumption of artificially sweetened (diet) drinks was not associated with a cancer risk.

Study of >100,000 French Adults

The French authors, led by Eloi Chazelas, from the Sorbonne Paris Cité Epidemiology and Statistics Research Center, note that "sugary drinks are convincingly associated with the risk of obesity, which in turn, is recognised as a strong risk factor for many cancers."

They set out to investigate whether there is a link between the consumption of sugary beverages and cancer — and they found a positive association.

The team analyzed data from the NutriNet-Santé cohort study, which involved 101,257 healthy French adults (21% men; 79% women; average age, 42 years).

Participants completed at least two 24-hour online validated dietary questionnaires that were designed to measure usual intake of 3300 different food and beverage items.

The team looked specifically at the daily consumption of sugary drinks (sugar-sweetened beverages and 100% fruit juices) and artificially sweetened (diet) beverages. They found that men drank a few more sugary drinks than women (average daily consumption, 90.3 mL vs 74.6 mL).

The participants were followed for an average of 5 years and for a maximum of 9 years (2009–2018).

During that time, 2193 first cases of cancer occurred. Cases were validated by medical records and were linked with health insurance national databases.

This total included 693 breast cancers, 291 prostate cancers, and 166 colorectal cancers. The average age at cancer diagnosis was 59 years.

Positive Association

From these results, the team calculated that an increase of 100 mL/day in the consumption of sugary drinks was associated with an 18% increased overall risk for cancer (subdistribution hazard ratio [HR] for a 100 mL/day increase, 1.18; 95% confidence interval, 1.10 – 1.27; P < .001).

Commenting on this finding, Graham Wheeler, PhD, senior statistician at Cancer Research UK and University College London, noted: "The mean daily intake of sugary drinks across all participants was about 93 mL. A 100-mL increase in daily intake of sugary drinks was associated with an 18% increase in the risk of developing some form of cancer. Participants were followed on average for about 5 years, and 22 participants per 1000 developed some form of cancer.

"So this means if 1000 similar participants increased their daily sugary drink intake by 100 mL, we'd expect the number of cancer cases to rise from 22 to 26 per 1000 people over a 5-year period. However, this assumes that there isa genuine causal link between sugary drink intake and developing cancer, and this still needs further research.

"The authors rightly caution that further large prospective studies will be needed to confirm their results," he commented.

The French researchers note that there was also a positive association for breast cancer specifically, with an increased risk of 22% (HR, 1.22; P = .004).

This link was stronger for premenopausal breast cancer (P = .02) than for postmenopausal breast cancer (P = .07), but the median consumption of sugary drinks was lower in menopausal women (88.2 mL/day) than in premenopausal women (43.2 mL/day), the team notes.

There was no association with prostate and colorectal cancers, but there were fewer cases of these cancers.

Sugary beverages included 100% fruit juice. When considered seperately, consumption of fruit juice was associated with a higher overall risk for cancer, as were the other sugary drinks.

Many Confounders Were Accounted for, but Limitations Remain

In contrast, the consumption of artificially sweetened (diet) beverages was not associated with an increased risk for cancer. However, the authors advise caution in interpreting this finding because the consumption of such drinks was low.

"This is an observational study, thus causality of the observed associations cannot be established and residual confounding cannot be entirely ruled out," they stress.

While acknowledging the limitations of their study, they also note that they adjusted for a wide range of confounding factors and performed many sensitivity analyses, and that none of these substantially modified the findings, which remained statistically significant and stable.

In addition, mechanistic data support these epidemiologic findings, they comment. Sugary drinks contribute to obesity, but they may also increase visceral fat, blood glucose levels, and inflammatory markers, all of which are known risk factors for cancer.

In conclusion, they state: "These data support the relevance of existing nutritional recommendations to limit sugary drink consumption, including 100% fruit juice, as well as policy actions, such as taxation and marketing restrictions targeting sugary drinks, which might potentially contribute to the reduction of cancer incidence."

Reactions to the Study

Several nutritional experts posted their reactions to this study on the website of the UK Science Media Center.

This is "a large, good quality study. The authors are aware of confounders, they are aware of the limitations of their dietary measurement techniques and the findings have been well reported," commented Amelia Lake, PhD, reader in public health nutrition, Teesside University, Middlesbrough, United Kingdom.

The research adds "to the overall picture of the importance of the current drive to reduce our sugar intake" and highlights why "controls on the marketing of high sugar products are so important not only in terms of obesity, but also possibly cancer prevention," she added.

Catherine Collins, RD, FBDA, a dietician for the UK National Health Service, suggested that one of the strengths of this French study is the way that details on diet were collected.

Participants recorded 3 days' worth of dietary records online every 2 years, which is "a more robust dietary assessment than a 24 hour 'What did you eat yesterday?' approach of many similar research groups," she observed.

Nevertheless, all self-reporting of dietary intake is limited in that it relies on participants to be both honest and accurate."

But Are Findings Biologically Plausible?

Collins also raised some doubts about the plausibility of the findings.

"Their findings suggested a 30% increase in 'all cancer' diagnosis in those with the highest intake of sugary drinks when compared to those with the lowest consumption," she noted.

"Those subjects with mid-range intakes of sugary drinks had no significant increase in cancer risk for breast or any other cancer.

"Just how much sugar from drinks was associated with this increased risk? Those in the lowest intake group consumed around 3 g (around half a teaspoon) of sugar from their daily drinks. Those in the highest group averaged 19 g a day — equivalent to four teaspoons of sugar.

"The risk appeared to be increased around the 10 g of sugar per day from drinks," she commented. "Could 7 g of sugar from the lowest to third quartile, equivalent to 1.5 teaspoons of sugar, or an additional 28 kcals a day, really make such a difference to cancer risk, especially in the absence of obesity within the group?

"I find the biological plausibility of this difficult, given there was no significant difference between groups in relation to body weight or incidence of diabetes which is often cited as an associated risk. Across the board, sugar calories from drinks ranged from almost 0% to nearly 4% of total calories, well within acceptable intakes associated with healthy eating recommendations."

She continued: "The highest sugar consumption from drinks was in the young adult age group, which were similar findings to other research groups around the world. The greater risk of breast cancer incidence in this younger group is disturbing, but may represent other factors not considered within this paper. For example, the percentage of pre-menopausal women using oral contraceptives increased with increasing sugar intake. Pre- and post-menopausal breast screening was not discussed, but could have contributed to a higher earlier and definitive diagnosis rate in women taking up screening before symptoms became apparent — unlike other cancers where symptoms appear first, leading to further investigation. These clinical situations were not addressed in the paper, " Collins stressed.

"Those in the higher sugary drink intake group had higher calorie intakes, higher salt intake and less calories from alcohol. All these factors suggest dietary differences of which sugary drink intake may just be a proxy marker and not a cause of the association," she added.

Main Message Should Focus on Diet Drinks

Collins concluded her comments by turning to one of the findings not highlighted by the French researchers.

"The take home message is the absence of cancer risk in using diet drinks containing artificial sweeteners," she emphasized.

"For too long the nutri-myth of sweeteners being a health risk has remained in popular culture. All current sweeteners in use have been through rigorous safety testing before being acceptable for human use. This study shows no impact of artificially sweetened drinks with cancer risk, adding to the body of knowledge from laboratory work to human studies confirming this.

"Adding sugar to hot or cold drinks adds no real nutritional benefit and contributes to total calorie load," and this new research supports "evidence for choosing sugar-free rather than sugary drinks," she concluded.

The NutriNet-Santé study was supported by several French public institutions, as detailed in the article. The authors, Lake, and Collins have disclosed no relevant financial relationships. Wheeler has received honoraria from Novametrics Consulting Ltd.

BMJ. Published online July 10, 2019. Full text

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