July 10, 2019

expert reaction to study looking at sugary drinks and cancer risk

A study, published in the The BMJ, reports a possible association between higher consumption of sugary drinks and an increased risk of cancer.

Dr Amelia Lake, Reader in Public Health Nutrition, Teesside University, said:

“This is a large study of 101,257 healthy French adults (21% men; 79% women) with an average age of 42 years.  This is an observational study so it cannot establish cause.  It 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.

“To measure their participants’ dietary intakes they completed at least two 24-hour online validated (checked) dietary questionnaires.  These are questionnaires designed to measure usual intake of 3,300 different food and beverage items.  Participants were asked to fill out more than two questionnaires on their dietary intake, but only those who filled out a minimum of two are included in their analysis.  Their participants were followed up for a maximum of 9 years (2009-2018).  Their results found that increased sugary drink consumption was associated with increased overall cancer risk and breast cancer risk.

“They did not find an association between the consumption of artificially sweetened (diet) beverages and risk of cancer.  However, in this study there was a low consumption of diet drinks.

“The authors have proposed some biological mechanisms why this increased cancer risk may be occurring.  For example effect of the sugar contained in sugary drinks on visceral fat which is stored around vital organs, blood sugar levels, and inflammatory markers.

“While this study doesn’t offer a definitive causative answer about sugar and cancer (not at all claimed by the authors), it does add to the overall picture of the importance of the current drive to reduce our sugar intake.  Clearly there is more work to be done and measuring dietary intake is challenging however, the message from the totality of evidence on excess sugar consumption and various health outcomes is clear – reducing the amount of sugar in our diet is extremely important.  This highlights why our UK Sugar Levy and controls on the marketing of high sugar products is so important not only in terms of obesity but also possibly cancer prevention.”

Dr Graham Wheeler, Senior Statistician, Cancer Research UK & UCL Cancer Trials Centre, said:

“This large, well-designed study adds to the existing evidence that consumption of sugary drinks may be associated with increased risk of some cancers.

“The strengths of this study are that over 100,000 participants were included, and that participants were repeatedly asked about their diet as they were followed up.  The analyses also adjusted for many factors, such as smoking status and physical activity levels, that may affect a person’s risk of developing cancer.

“However, as participants were self-selecting, these findings may not be generalisable to the wider population.

“The mean daily intake of sugary drinks across all participants was about 93ml.  A 100ml 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 five 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 100ml, 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 is a genuine causal link between sugary drink intake and developing cancer, and this still needs further research.

“Whilst there was some evidence for an association between sugary drink consumption and the risk of developing breast cancer, the same association was not found for colorectal or prostate cancers.  Further research into the biological mechanism between sugary drink consumption and specific cancers is needed to establish if one does indeed cause the other.”

Dr Ian Johnson, Nutrition researcher and Emeritus Fellow, Quadram Institute Bioscience, said:

“This is a relatively large, well designed prospective study of French adults.  The consumption of food items and drinks was repeatedly measured, using validated dietary questionnaires, and new cases of cancer were recorded using robust methods.

“The results indicate statistically significant correlations between the consumption of sugar-sweetened drinks and risk of all cancers combined, and of breast cancer.  Surprisingly perhaps, the increased risk of cancer in heavier consumers of sugary drinks was observed even among consumers of pure fruit juice – this warrants more research, but this finding from this study is not, on its own, enough to suggest extending the sugar tax to cover pure fruit juice.  Artificially sweetened drinks were not associated with cancer, although the authors note that this observation may not be reliable, as consumption of artificial sweeteners was relatively low in their study group.

“As with all observational studies, it cannot be assumed that statistical correlation necessarily indicates causality.  For example, total consumption of sugary beverages might be acting as a marker for some other unidentified aspect of a dietary pattern linked to higher risk of cancer.

“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.

“However, the authors rightly caution that further large prospective studies will be needed to confirm their results.  In the mean-time, this study adds further evidence in support of public health measures to discourage the over-consumption of sugar-sweetened drinks.”

Catherine Collins RD FBDA, NHS dietitian, said:

“This report from the NutriNet-Santé research group monitoring the diet and lifestyle of over 100,000 French adults suggests a positive association between an increased consumption of sugary drinks and overall risk of cancer, particularly breast cancer.  Launched in 2009, the researchers analysed the online recorded dietary data from over 100,000 French adults, who recorded three days’ worth of dietary records online every two years and compared this to cancer diagnosis.  A three-day record, repeated every two years or so, generates more robust dietary assessment than a 24 hour ‘What did you eat yesterday?’ approach of many similar research groups.

“Their findings suggested a 30% increase in ‘all cancer’ diagnosis in those with the highest intake of sugary drinks when compared to those in with the lowest consumption, a third of cancers attributed to the reported incidence in breast cancer in this group comprising 78% women.  Compared to those with the lowest sugary drink intakes recorded, premenopausal women consuming the highest intakes of sugary drinks had a 28% increased risk of breast cancer, post-menopausal women a 44% increase.

“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 3g (around half a teaspoon) of sugar from their daily drinks.  Those in the highest group averaged 19g a day – equivalent to four teaspoons of sugar.  Risk appeared to be increased around the 10g of sugar per day from drinks.  Could 7g of sugar from the lowest to third quartile, equivalent to 1.5 teaspoons of sugar, or an additional 28kcals 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% total calories, well within acceptable intakes associated with healthy eating recommendations.

“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-menopause 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.

“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.

“In summary, these findings are interesting, but the take home message is the absence of cancer risk in using diet drinks containing artificial sweeteners.  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.  For healthy weight adults to self-report dietary intakes via an on-line portal is subject to the same limitations related to honesty and accuracy of recording suffered by all diet recording techniques.  This study in normal weight French women and men is of interest and worthy of further investigation and adds to the evidence of choosing sugar free rather than sugary drinks.”

‘Sugary drink consumption and risk of cancer: results from NutriNet-Santé prospective cohort’ by Eloi Chazelas et al. was published in the BMJ at 23:30 UK time on Wednesday 10 July 2019. 

DOI: 10.1136/bmj.l2408

Declared interests

Dr Amelia Lake: “Amelia Lake is a dietitian and registered nutritionist (public health) she works as a Reader in Public Health Nutrition at Teesside University and is Associate Director of Fuse, The Centre for Translational Research in Public Health.”

Dr Graham Wheeler: “I am a employed by UCL, am a Fellow and Statistical Ambassador of the Royal Statistical Society, and a voluntary research committee member for Chiltern Music Therapy, a not-for-profit organisation providing music therapy services.  I have previously received honoraria from Novametrics Consulting Ltd.”

Dr Ian Johnson: “Ian Johnson was an external member of the UK SACN working group on Carbohydrates and Health, which reported in 2015.”

Catherine Collins: “No conflict of interest declared.”