Do sugary drinks cause cancer?

"A small glass of juice or soda a day can increase the risk of cancer," said a recent CNN headline … "A single drink of fruit juice or sweet tea a day can dramatically increase the risk of cancer, according to a major study, was the decision of DailyMail.com.

The study behind the headlines is here, and in its context, it's a valuable contribution to science on sugar, health and disease.

But that's all: the context.

There has been a stack of observational studies on the correlation between sugar and cancer over the past decades, well summarized in this systematic review of 2018. But it is still advisable to determine where the latest study is. global search puzzle, and this little neat graph of @ dnunan79 on Twitter it's really good:

In the graph, Nunan added the new findings (Chazelas et al 2019) to the pre-existing evidence from the 2018 systematic review, especially for breast cancer and sugar consumption (where the link seems strongest) for more Information about this later).

As the chart indicates, most previous studies on breast cancer and sugar have shown no association between sugars contained in foods and beverages, but rather harmful associations on sugary drinks .

Does the latest study add weight to the suggestion that sweetened drinks only increase the risk of cancer? Maybe, maybe not.

Let's examine the study with a little depth. Coming from the NutriNet-Santé research group in France, it was large and well designed. He monitored the diet and lifestyle of more than 100,000 French adults for a period of up to nine years and collected the ingestion records more robustly than many studies. food assessment. Rather than taking a "what did you eat yesterday?" Approach, participants repeated the three-day registrations every two years.

All drinks containing more than 5% sugar were considered sweet drinks in the study, including pure fruit juices, sodas, energy drinks, hot drinks with added sugar and milkshakes. The researchers followed the participants over time to see if those who drank the most of these drinks were more likely to develop cancer.

The results showed that for breast cancer in particular (the group was 78% female), pre-menopausal women who had the highest intake of sugary drinks had an increased risk of 28%; in postmenopausal women, this was an increase of 44%. (For colorectal or prostate cancer, no association has been found.)

When looking at cancer as a whole, each additional 100 mL of any sugary beverage consumed by a person each day is associated with an 18% increase in cancer risk.

An 18% increase in risk corresponds to 4 additional cases of cancer per 1000 people over a period of 5 years. In other words, if 1000 similar participants increased their daily consumption of 100ml sweetened beverages, the results could predict an increase in the number of cancer cases from 22 to 26 per 1,000 people over a 5-year period .

Of course, this assumes that there is a real causal link between the consumption of sugary drinks and the development of cancer. Do we have enough information to infer? No, we do not do it. Although the authors have attempted to control several potential confounding factors, including diet, age, sex, exercise, and use of hormonal contraceptives, this is an excessive effort.

This is not simply because it would mean that sugar in beverages causes cancer but not total sugar in the diet (which would be strange). This is also because of the way in which a cause and effect association seems unlikely when you determine the amounts of sugar that confer increased risk.

In the study, people in the lowest quartile of sugary drinks consumed 3 g of sugar daily, and those in the top quartile consumed 19 g. But the risk of cancer has actually increased in the third quartile, to about 10 g of sugar per day from sugary drinks. A sugar intake of 7 g, or 1 ½ teaspoon per day, is it really enough to make such a difference in cancer risk, especially since obesity is not a factor in this population?

This would seem biologically improbable.

Instead, it is much more likely that other factors are difficult to control. People in the group with higher consumption of sugary drinks had higher caloric intake, higher salt intake, and fewer calories from alcohol, suggesting dietary differences, as the consumption of sugary drinks may be simply an indirect indicator. Higher sugar consumption may also indicate other risk factors that are not at all related to the diet.

An interesting aspect of this study should not be overlooked: the authors also examined "dietetic" drinks and found no link between sweetened drinks and cancer. It is fair to say that dietary drinks were not widely consumed in this group, but given the widespread belief in pop-nutrition circles that aspartame and other sweeteners are carcinogens, it is really what you need.

In the round? This is an interesting article that, overall, adds to the evidence of the choice of sugar-free beverages rather than sugary drinks. But the authors rightly point out that other large prospective studies are needed. And much more research on possible biological mechanisms is needed to determine whether sugar actually contributes to cancers, particularly breast cancer.