Some artificial sweeteners may not be a good alternative to sugar and could push up the risk of cancer, scientists have suggested.
Experts from the French National Institute for Health and Medical Research, and Sorbonne Paris Nord University, analysed data and suggested a potential increased risk for breast cancer and obesity-related cancers.
Previous large-scale studies on humans have found no such association and UK experts said no causal link had been found.
If true, the finding would relate to about three more cancer cases per 10,000 people over eight years, according to one analysis of the findings.
The European Food Safety Authority (EFSA) has said artificial sweeteners are not harmful within daily limits. For aspartame, the daily limit is equivalent to 12 cans of diet drink.
The new study, published in PLOS Medicine, examined data for 102,865 French adults as part of the NutriNet-Sante study.
The people in the research self-reported their medical history, diet, lifestyle habits and other health data.
Researchers looked at artificial sweetener intake from their dietary records and also looked at the diagnoses of cancer.
They adjusted for many factors that may influence the findings, such as age, sex, education, exercise levels, smoking, body mass index, height and family history of cancer.
The findings suggested those people consuming larger quantities (typically 79mg per day) of artificial sweeteners had a 13% higher risk of overall cancer compared to those having none.
The findings were strongest for aspartame and acesulfame-K, both sweeteners that are approved in the UK.
Higher risks were observed for breast cancer (22% increased risk for aspartame) and obesity-related cancers, the scientists said.
The study had several limitations, including that those in the study were more likely to be women and to be health-conscious.
The researchers said: “Our findings do not support the use of artificial sweeteners as safe alternatives for sugar in foods or beverages and provide important and novel information to address the controversies about their potential adverse health effects.
“While these results need to be replicated in other large-scale cohorts and underlying mechanisms clarified by experimental studies, they provide important and novel insights for the ongoing re-evaluation of food additive sweeteners by the European Food Safety Authority and other health agencies globally.”
Dr Michael Jones, senior staff scientist in genetics and epidemiology at the Institute of Cancer Research (ICR), London, said the current consensus “is that there is no clear evidence that artificial sweeteners cause cancer in humans”, although the issue is frequently looked at.
He added: “The link between artificial sweeteners and cancer reported in this study does not imply causation – it is not proof that artificial sweeteners cause cancer.
“The types of people who use artificial sweeteners may be different in many ways to those who do not, and these differences may partly or fully explain the association.”
Fiona Osgun, senior health information manager at Cancer Research UK, said: “This large study suggested there’s an association between some artificial sweeteners and cancer, but that doesn’t mean they cause it or that people need to avoid them.
“While the researchers have tried to find out what people were eating and account for other factors that could affect cancer risk, this is a single study that relies largely on self-reports.
“What we eat and drink overall is much more important than one single element of our diet – so aim to eat more fruit, veg and wholegrains, and cut back on red and processed meats and foods high in fat, sugar and salt.”
Dr Duane Mellor, from Aston University, said the findings related to about “three more cases of all types of cancer per 10,000 people over an average of about eight years”.
He pointed to flaws in the study, adding: “This study does not prove or even suggest that we should go back to sugar and turn our backs on artificial sweeteners or diet drinks.”
Professor Tom Sanders, from King’s College London, said: “It is well known that women who are obese or who have a tendency to gain weight are more likely to use artificial sweeteners and this limits the validity of the conclusions of this study because it is not possible to completely control for this in the statistical analysis.”
Dr Kotryna Temcinaite, senior research communications manager at Breast Cancer Now, said: “What we do know is that eating a balanced diet, maintaining a healthy weight and being physically active are steps people can take to help reduce their risk of breast cancer.”