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Sugary drinks linked to cancer

Thursday 11 July 2019

"Drinking a third of a fizzy drink a day 'increases risk of breast cancer by 22% – and fruit juice is just as dangerous'," reports the Sun.

The headline is based on a large ongoing study that assessed sugary and artificially sweetened drink intake in more than 100,000 adults in France.

All drinks with high levels of sugar were considered, including 100% fruit juices and sugary fizzy drinks.

The researchers followed the participants up over time to see whether those who drank more of these drinks were more likely to develop cancer.

They found that each additional 100ml of any sugary drink a person drank a day increased cancer risk by 18%.

An increase in cancer risk was also found with 100% fruit juices, but not with artificially sweetened drinks.

An 18% increase in risk may sound quite high, but it corresponds to 4 extra cases of cancer per every 1,000 people over a 5-year period.

This was a good-quality study, but it's difficult to pinpoint the impact of 1 part of a person's diet on their health. Ideally, more studies are needed to assess this link.

But we already know that consuming too much sugar is not good for us.

If we consume more calories (in any form) than we burn off, we can become overweight and being overweight increases cancer risk.

Drinking too many sugary drinks is also bad for our teeth.

Healthy lifestyle changes are the most effective way to reduce your cancer risk.

These include regular exercise, eating a healthy diet, avoiding smoking and not drinking too much alcohol.

Where did the story come from?

This study was conducted by researchers from the Paris 13 University, Avicenne Hospital and The French Public Health Agency.

It was funded by various public bodies in France, including the Ministry of Health, the National Institute for Health and Medical Research (INSERM), the National Institute for Agricultural Research (INRA), and the Conservatoire National des Arts et Métiers (CNAM).

One of the researchers was funded by the French National Cancer Institute and the Fondation de France.

The study was published in the peer-reviewed British Medical Journal. The paper is open access, so you can read the study for free online.

This story has had extensive coverage in the UK media. While the reporting was broadly accurate, many headlines were alarmist, such as the Mail Online's claim that "Just ONE drink of fruit juice or sugary tea a day can dramatically increase the risk of cancer".

Focusing on an increase in relative risk without putting it into the context of actual risk (absolute risk) is not particularly helpful for readers.

Also, many headlines did not make it clear that we cannot be sure that sugary drinks are directly causing the increase in risk.

What kind of research was this?

This was an analysis of an ongoing prospective cohort study called the French NutriNet-Santé cohort, which was designed to assess how people's diets affect their health.

The analysis looked at whether drinking sugary or artificially sweetened drinks was linked to a person's risk of developing cancer.

Although lots of studies have looked at the links between sugary drinks and metabolism, weight and heart health, fewer studies have looked at whether they're linked to cancer.

Those studies that have been done have not consistently found a link, so the researchers wanted to carry out a large prospective cohort study to look at this question.

This type of study is the best way to look at the link between diet and health outcomes over a long period of time.

As people make their own lifestyle choices, and these can also be influenced by socioeconomic and other factors, this means people who drink more sugary drinks may have different behaviours or characteristics from those who drink less.

These differences can influence this type of analysis, meaning we cannot be certain sugary drinks are directly causing any links seen.

Researchers can take steps to try to reduce the impact of other factors, as they have done in this study, and this makes the results more robust.

What did the research involve?

Researchers in the NutriNet-Santé study used mass media campaigns to recruit adults to take part.

The study is web-based, and participants complete questionnaires and follow-up online.

It started in 2009 and is still ongoing. The current analysis used data collected up to 2017.

Once they registered, participants completed 5 questionnaires about their diet (food and drink), physical activity, health, sociodemographic and lifestyle characteristics, and height and weight.

They were also asked to report their weight and record their diet every 6 months.

Diet was assessed using a standard questionnaire, which asked participants to record what they ate on 3 non-consecutive days (2 weekdays and 1 weekend day) over a 2-week period.

The diet questionnaire included 97 types of sugary drinks and 12 types of artificially sweetened drinks.

Sugary drinks were defined as those including more than 5% simple carbohydrates (sugars) and 100% fruit juices.

It included sugar-sweetened hot beverages, as well as cold drinks, fizzy and non-fizzy drinks, and energy and sports drinks.

On average, these beverages contained just under 11g of sugar per 100ml (median).

The researchers carried out various checks to see how accurately participants were reporting their information.

For example, a small group of participants were seen by the researchers in person to check that weight was being reported accurately.

Participants who showed signs of under-reporting their dietary intakes were excluded.

Participants filled in a yearly questionnaire about their health and could also report a health event at any time.

If a person reported having developed cancer, a doctor from the study team contacted them to ask them to provide relevant medical records.

The researchers followed up with the person's hospital or doctor as needed.

They also looked for other cases of cancer or deaths from cancer among participants using the national health insurance system and death register.

Details of all cases were reviewed by a panel of doctors to confirm that cancer was present.

The researchers then analysed whether people who drank more sugary or artificially sweetened drinks at the start of the study were more likely to go on to develop cancer.

They took into account other factors that could affect the results (confounders).

These included:

  • age
  • sex
  • education
  • other dietary factors, such as energy intake, alcohol consumption, and fruit and vegetable consumption
  • body mass index (BMI)
  • physical activity
  • health conditions, such as type 2 diabetes
  • family history of cancer

For the analyses of breast cancer specifically, they also took into account the number of children the person had, if they'd gone through the menopause, and use of oral contraception or hormone replacement therapy.

What were the basic results?

The analysis included 101,257 adults who did not have cancer when they signed up to take part, and who completed at least 2 questionnaires about their diet in the first 2 years of the study.

Those who drank the most sugary drinks consumed an average of 186ml a day, and those who drank the least an average of 93ml a day.

Most of the participants (78.7%) were women.

The participants were followed up for an average (median) of 5 years. During follow-up, 2,193 people developed cancer (about 2%).

After taking into account other factors, participants who drank more sugary drinks were more likely to develop cancer.

For each 100ml extra of sugary drinks a person drank daily, their risk increased by 18% relative to those drinking 100ml less per day (hazard ratio [HR] 1.18, 95% confidence interval [CI] 1.10 to 1.27).

When looking at specific cancer types, women who drank more sugary drinks were more likely to develop breast cancer (for an extra 100ml per day HR 1.22, 95% CI 1.07 to 1.39).

No link was found between sugary drink intake and with prostate or bowel cancer.

When looking at specific types of drinks, 100% fruit juice was associated with overall cancer rate (for an extra 100ml per day HR 1.12, 95% CI 1.03 to 1.23).

Artificially sweetened drinks were not found to be linked with cancer risk, but the participants drank relatively little of these drinks (with half of participants drinking less than 7ml per day on average).

How did the researchers interpret the results?

The researchers concluded their study found that drinking more sugary drinks, including 100% fruit juice, is associated with an increase in risk of cancer.

They say their findings need to be confirmed by other large prospective studies.

Conclusion

This study has shown a link between drinking more sugary drinks and risk of cancer.

It has a number of strengths, including its large size, recording diet on more than 1 occasion, and long period of follow-up.

The researchers carried out a number of steps to ensure the data they were collecting online was likely to be correct.

They also took into account many of the factors that could influence the results in their analyses.

It's important to understand exactly what the 18% increase in cancer risk found in this study means. It's relatively small: about 22 out of every 1,000 of people developed it.

Based on the findings, if everyone in the study consumed an extra 100ml of sugary drink per day (but everything else stayed the same), they might have expected this to increase to about 26 out of every 1,000 people developing cancer during the study.

Of course, this would only be the case if the sugary drinks were directly causing the increase in cancer risk, which is uncertain.

It's also worth noting that the study relied on people volunteering to take part, was mainly in women, and was only carried out in France.

The results may not be representative of what they would be in the wider population in France, or in other countries.

Identifying the direct impact of a specific part of the diet on health is challenging, and the researchers acknowledge that their results need to be confirmed in other large prospective studies.

Scientific research will also need to look at how sugary drinks might contribute to cancer risk, and whether it's the sugar having an effect or other components of the drinks.

Making healthy lifestyle changes is the most effective way to reduce your cancer risk.

These include regular exercise, eating a healthy diet, avoiding smoking and not drinking too much alcohol.

Analysis by Bazian
Edited by NHS Website