The consumption of sugary drinks, including fruit juice, has been positively associated with the overall risk of cancer and the risk of breast cancer in a large prospective study conducted in France.
Although the study is observational and therefore cannot establish causality, the researchers suggest that "sugary drinks, which are widely consumed in Western countries, could represent a modifiable risk factor for cancer prevention".
The research was published online on 10 July in the BMJ
Nutrition experts who reacted the findings were told that the trial was well designed and agreed that it adds ammunition to public health policies, such as the imposition of taxes, which discourage excessive consumption of sugary drinks.
One expert, however, questioned some of the findings and stated that the main message of the study should be the fact that the consumption of artificially sweetened drinks (diet) was not associated with a cancer risk.
Study of> 100,000 French adults
The French authors, led by Eloi Chazelas, of the Cité Epidemiology and Statistics Research Center of the Sorbonne in Paris, observe that "sugary drinks are convincingly associated with the risk of obesity, which in turn is recognized as a strong risk factor for many cancers ".
They decided to investigate if there is a link between the consumption of sugary drinks 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 validated 24-hour online dietary questionnaires that were designed to measure the usual intake of 3300 different foods and beverages.
In particular, the team examined the daily consumption of sugary drinks (sugary drinks with sugar and 100% fruit juices) and artificially sweetened (dietary) drinks. They found that men drank slightly more than 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. The cases were validated by medical records and linked to the national health insurance databases.
This total included 693 breast cancers, 291 prostate cancers and 166 colorectal cancers. The average age at cancer diagnosis was 59 years.
From these results, the team calculated that an increase of 100 ml / day in the consumption of sugary drinks was associated with an increase in the overall risk of 18% for cancer (risk of under-distribution (HR) for an increase of 100 ml / day, 1.18; 95% confidence interval, 1.10 – 1.27; P <.001).
Commenting on this result, Graham Wheeler, PhD, senior statistician at Cancer Research UK and University College London, noted: "The average daily intake of sugary drinks among all participants was approximately 93 ml. An increase of 100 ml in the 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, if 1000 similar participants increased the daily intake of 100 ml sweetened sugary drinks, we would expect the number of cancer cases to increase from 22 to 26 per 1000 people over a 5-year period. However, this assumes that true causal link between the intake of sugary drinks and the development of cancer, and this still requires further research.
"The authors rightly warn that further broad 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 in particular, with an increase in risk of 22% (HR 1.22; P = .004).
This link was stronger for premenopausal breast cancer (P = 0.02) compared to postmenopausal breast cancer (P = 0.07), but the average 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 tumors.
Sweetened drinks included 100% fruit juice. When considered separately, consumption of fruit juice was associated with a higher overall risk of cancer, as were other sugary drinks.
Many confounders have been considered, but limitations remain
Conversely, the consumption of artificially sweetened drinks (diet) was not associated with an increased risk of cancer. However, the authors advise caution in interpreting this result because the consumption of such drinks was low.
"This is an observational study, so the causality of the observed associations cannot be established and the residual confounding cannot be completely ruled out," they emphasize.
While acknowledging the limitations of their study, they also note that they have adapted to a wide range of confounding factors and have performed numerous sensitivity analyzes, and that none of these has substantially changed the results, which have remained statistically significant and stable.
Moreover, the mechanical data support these epidemiological results, they comment. Sweetened drinks contribute to obesity, but they can 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 importance of existing nutritional recommendations for limiting the consumption of sugary drinks, including 100% fruit juice, as well as political actions, such as tax and marketing restrictions that target sugary drinks, which could potentially contribute to reducing the incidence of cancer. "
Several nutritionists have published their own reactions to this study on the UK Science Media Center website.
This is "a large and good quality study: the authors are aware of the confounders, they are aware of the limitations of their diet measurement techniques and the findings have been well reported," commented Amelia Lake, PhD, public nutrition reader, Teesside University, Middlesbrough, United Kingdom.
The research adds "to the overall picture of the importance of the current tendency to reduce sugar intake" and underlines why "controls on the marketing of high-sugar products are so important not only in terms of of obesity, but also of cancer prevention "she added.
Catherine Collins, RD, FBDA, a dietician from the British National Health Service, suggested that one of the strengths of this French study is the way the details of the diet were collected.
Participants recorded a record of 3-day online food records every 2 years, which is "a more solid dietary assessment than a 24-hour" What did you eat yesterday? "approach of many similar research groups," he noted.
Nevertheless, all self-reporting on food intake is limited as it is based on both honest and accurate participants. "
But are the results biologically plausible?
Collins also raised some doubts about the plausibility of the results.
"Their findings suggested a 30% increase in the diagnosis of" all cancers "in those with the highest intake of sugary drinks compared to those with the lowest consumption," he noted.
"Subjects with mid-range intake of sugary drinks did not have a significant increase in the risk of breast cancer or any other cancer.
"How much sugar from drinks was associated with this increased risk? Those in the lower intake group consumed about 3 g (about half a teaspoon) of sugar from their daily drinks. Those in the highest group have an average of 19 g per day – equivalent to four teaspoons of sugar.
"The risk seemed to have increased around 10 g of sugar a day from drinks," he commented. "Could be 7 g of sugar from the lowest to the third quartile, equivalent to 1.5 teaspoons of sugar, or an additional 28 kcal per day, really making such a difference to the risk of cancer, especially in the absence of obesity at all; inside the group?
"I find the biological plausibility of this difficult, given that there was no significant difference between the groups in relation to body weight or incidence of diabetes, which is often cited as an associated risk. In general, calories sugars from drinks ranged from almost 0% to almost 4% of total calories, well within the acceptable intakes associated with healthy food recommendations. "
He continued: "The highest consumption of beverage sugars was in the group of young adults, which were similar to other research groups around the world. The greatest risk of breast cancer incidence in this younger group is disturbing, but may represent other factors not. For example, the percentage of pre-menopausal women who use oral contraceptives has increased with increasing sugar intake. Breast screening before and after menopause has not been discussed, but could having contributed to a higher rate of early diagnosis in women considering screening before symptoms became apparent, unlike other tumors where symptoms appear first, leading to further investigation. These clinical situations were not treated in document, "said Collins.
"Those in the highest sugared beverage intake group had higher caloric intake, higher salt intake and fewer calories from alcohol." All these factors suggest dietary differences of which the intake of sugary drinks can only be an indicator and not a cause of the association, "she added.
The main message should focus on diet drinks
Collins concluded his comments by addressing one of the findings not highlighted by French researchers.
"The message to take home is the absence of cancer risk in the use of diet drinks containing artificial sweeteners," he stressed.
"For too long the nutritional myth of sweeteners is a health risk remained in popular culture. All current sweeteners in use have been subjected to rigorous safety tests before being acceptable for human use. This study does not shows the impact of artificially sweetened drinks with a risk of cancer, adding to the body of knowledge from laboratory work to studies on man that confirm it.
"The addition of sugar to hot or cold beverages does not provide any real nutritional advantage and contributes to the total caloric load", and this new research supports "evidence for choosing sugar-free rather than sugary drinks," he concluded.
The NutriNet-Santé study was supported by several French public institutions, as detailed in the article. The authors, Lake and Collins, did not disclose relevant financial reports. Wheeler has received honor from Novametrics Consulting Ltd.
BMJ. Published online 10 July 2019. Full text
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