- A large prospective cohort study of more than 100,000 French adults between 2009 and 2017 found:
- Increased sugary drink consumption was associated with an increased risk of cancer;
- Increased consumption of 100 per cent fruit juice was associated with an increased risk of cancer;
- Conversely, the consumption of low-calorie sweetened beverages, water and unsweetened tea and coffee was not associated with risk of cancer.
- Beverage consumption was assessed from self-reported dietary records.
- Cancer cases were also self-reported.
- The objective of this study is not to determine whether sugary beverages cause cancer, but rather to assess how certain levels of consumption might be related.
- According to the National Cancer Institute, “no studies have shown that eating sugar will make your cancer worse or that, if you stop eating sugar, your cancer will shrink or disappear. However, a high-sugar diet may contribute to excess weight gain, and obesity is associated with an increased risk of developing several types of cancer.”
- 2015-2020 Dietary Guidelines for Americans recommend limiting the intake of added sugars to less than 10 per cent of total calories per day.
A new study published in The BMJ is making the news, receiving media attention for its examination of self-reported consumption of sugary drinks and risk for cancer. You’ve probably seen the headlines by now, but have you read the study? We have. Here’s our take.
How was the study done?
The purpose of this study was to examine the association of various beverages and the risk for cancer. This data comes from the French NutriNet-Santé cohort, which followed more than 100,000 cancer-free French adults between 2009 and 2018. The age of study participants at enrollment ranged from 18 to 72 years old, with the average being 42. The subjects were majority female (79 per cent) and the median follow-up time for each person in the study was about five years.
To collect dietary information, at the beginning of the study and every six months thereafter, participants filled out three non-consecutive validated web-based 24-hour dietary records during a two–week period. Of the three diet records, two were taken on weekdays and one on a weekend day. The study focused on beverage consumption and collected information on other diet and lifestyle components such as smoking and intake of carbohydrates, fat, sodium and alcohol.
Cancer cases were also self-reported. Medical records were available for more than 90 per cent of the reported cancer cases and 95 per cent of those were confirmed by research physicians.
What were the results?
The study found that higher consumption of sugary drinks was associated with an increased risk of overall cancer and breast cancer. Increased consumption of 100 per cent fruit juices was associated with the risk of overall cancer. Conversely, the consumption of low-calorie sweetened beverages, water and unsweetened tea and coffee was not associated with risk of cancer.
Researchers divided the data into four levels of beverage intake. When comparing the subjects with the highest intake of sugary beverages with the lowest, they found that the highest consumers tended to be younger, more educated, less physically active, have less family history of cancer and have less prevalent cardiometabolic diseases. Additionally, they had higher intakes of calories, carbohydrate, dietary fat, sodium and drank less alcohol. They also were slightly more likely to be a current smoker.
In total, 2,193 cancer cases were diagnosed during the study: 693 breast cancers, 291 prostate cancers and 166 colorectal cancers. To understand the potential association between sugary drinks and cancer, absolute and relative risks are important to discuss and are explained below. Absolute risk is calculated as the number of events (i.e., new cancer cases) measured in a group divided by the number of people in that group. The absolute risk for all cancer development in this study population was 2.16 per cent (2,193 new cases in 101,257 total subjects). Relative risk is a calculation of how much of an effect a change might have. In this study, the relative risk for cancer development with a per day increase of 100 millilitres (or about 1/3 cup) of sugary beverages and 100 per cent fruit juice increased by 18 per cent and 12 per cent, respectively.
Interestingly, researchers also noted that the association between sugar-sweetened soda and cancer rate was “borderline nonsignificant,” or about a 3 per cent increase in relative risk for every additional 100 millilitres consumed per day. Because consumption was low in this population, the data were not reported.
The researchers hypothesize various physiological mechanisms to explain their observations, but none were tested in the study which would make commenting on them speculative at best.
Study strengths and limitations
The strength of this study is its large sample size. Collecting diet records from more than 100,000 subjects is impressive and means there is a lot of information to sift through.
That said, some subjects are more rigorous and compliant with their diet records than others. The study authors acknowledge this inherent challenge in nutrition epidemiology when stating, “a compromise has to be found between a high number of records per patient (better accuracy of the data but higher selection bias towards a very compliant population) or conversely, a smaller number of dietary records (lower degree of precision but lower selection bias compared with the general population). There is no perfect answer, thus we tested and presented the different possibilities, which showed consistent results.”
We’ve talked about the limitations of observational studies time and time again. Observational studies are often important first steps in building the greater body of scientific understanding. But they are not designed to establish cause and effect (in this case whether sugary drinks cause cancer) and therefore must be interpreted with caution. Observational studies can inform experimental studies (e.g., randomized controlled trials) which are designed to test cause and effect.
The objective of this study is not to determine whether drinking sugary beverages cause cancer, but rather to assess how certain levels of consumption might be related. Yet, randomized controlled trial evidence to date has not established a direct casual relationship between sugar and cancer.
There are many risk factors for developing cancer. While the amount of sugar you eat can play a role in your health, sugar by itself is not a risk factor for cancer. According to the National Cancer Institute, “no studies have shown that eating sugar will make your cancer worse or that, if you stop eating sugar, your cancer will shrink or disappear. However, a high-sugar diet may contribute to excess weight gain, and obesity is associated with an increased risk of developing several types of cancer.”
Sugars (natural and added) can be part of a healthy eating pattern, but they should be only a small part of what we eat. The 2015-2020 Dietary Guidelines for Americans recommend limiting the intake of added sugars to less than 10 per cent of total calories per day. Being mindful of how many calories we eat and drink, including those from added sugar, is important.
(This story originally appeared on foodinsight.org)