Common preservatives used to keep food safe and extend shelf life may be linked to a higher risk of several cancers and type 2 diabetes, according to two new studies in France.
“These findings are very important for preservatives that are not only widely used in the French and European markets, but also in the United States,” said lead author Mathilde Touvier, principal investigator of the NutriNet-Santé study used to conduct the research.
The NutriNet-Santé study, which began in 2009, compares more than 170,000 participants’ web-based diet and lifestyle reports with their medical data stored in the French national health care system.
“These are the first two studies in the world to investigate the associations between exposure to these food additives and cancer and type 2 diabetes,” said Touvier, who is also the director of research at the National Institute of Health and Medical Research in Paris, “and so we have to be very cautious about the message. Obviously, the results need to be confirmed.”
Despite these warnings, “high concern about preservatives is one more reason among many to emphasize the importance for personal and public health of fresh, whole, minimally processed, primarily plant foods,” Dr. David Katz said in an email.
Katz, who was not involved in the study, is a preventive and lifestyle medicine specialist who founded the True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.
Cancer and preservatives
The cancer study, published Wednesday in BMJ journal, closely examined the impact of 58 preservatives on about 105,000 people who were cancer-free in 2009 and were followed for up to 14 years. Only those who frequently completed 24-hour brand-specific questionnaires were included. People who ate the most foods with preservatives were compared to those who ate the least.
The researchers did an in-depth look at 17 preservatives consumed by at least 10% of the participants and found that 11 of them had no link to cancer. However, the six that have been linked to cancer are considered GRAS, or “generally recognized as safe” in food by the US Food and Drug Administration. These include sodium nitrite, potassium nitrate, sorbates, potassium metabisulfite, acetates, and acetic acid.
Sodium nitrite, a chemical salt commonly used in processed meats such as bacon, ham and deli meats, has been associated with a 32% increased risk of prostate cancer. Its cousin, potassium nitrate, was associated with a 22% higher risk of breast cancer and a 13% increase in all cancers. The World Health Organization has long considered processed meat a carcinogen, with a direct link to colon cancer.
Sorbates, especially potassium sorbate, have been associated with a 26% higher risk of breast cancer and a 14% increase in all types of cancer. These water-soluble salts are used in wine, pastries, cheeses, and sauces to prevent molds, yeasts, and some bacteria.
Potassium metabisulfite, often used in winemaking and brewing, was associated with a 20% increase in breast cancer and an 11% higher risk of all cancers, according to the study.
Acetates, which come from natural fermentation and are used in foods such as meat, sauces, bread and cheese, have been linked to a 25% higher risk of breast cancer and a 15% increase in cancer overall. Acetic acid, the main ingredient in vinegar, was associated with a 12 percent increased risk of all cancers, the study found.
Other types of preservatives have also been studied – antioxidants such as vitamin C, vitamin E, plant extracts such as rosemary, and synthetic preservatives such as butylated hydroxyanisole. While these more “natural” preservatives are often linked to a lower risk of cancer when eaten as whole foods, they can be harmful when used as additives, Touvier said.
“The hypothesis here is that when you isolate a substance from its original matrix of a whole fruit or vegetable, the action on our health may be different depending on how our gut microbiota will digest it,” she said.
Only two antioxidant preservatives have been linked to cancer, the study found. Sodium erythorbate and other erythorbates, which are made from fermented sugars, have been associated with a 21% higher incidence of breast cancer and a 12% increase in cancer overall.
Erythorbates are used to prevent discoloration and spoilage in poultry, soft drinks, and bakery products, to name a few. Sodium erythorbate is often used in processed meats to speed up the curing process.
Observational studies are subject to error due to the lack of control over variables that could also influence the results. However, a strength of this study was its ability to adjust for preservatives from natural sources and other food additives, as well as “detailed assessment of preservative intake through repeated 24-hour dietary records,” according to an editorial published with the study.
“We also looked at what colleagues have published about the impact of these preservative chemicals on animal models, cell models, gut microbiota, oxidative stress and inflammatory processes that might explain what we’re seeing,” Touvier said.
In addition, both studies controlled for confounders such as physical activity, tobacco, alcohol use, medication use and lifestyle factors, Touvier said.
“The finding that certain classes of preservatives are associated with increased risk of certain types of cancer was robust to all these adjustments, indicating that it is a matter that deserves respect and warrants further research,” Katz said.
Type 2 diabetes and preservatives
The type 2 diabetes study, published Wednesday in the journal Nature Communications, examined the role of preservatives and the potential risk of type 2 diabetes in nearly 109,000 NutriNet-Santé participants who did not have the disease at the start of the study.
Twelve of the 17 preservatives the researchers examined were linked to a nearly 50 percent higher risk of developing type 2 diabetes in people who consumed the highest levels.
Five of the same preservatives that caused cancer – potassium sorbate, potassium metabisulfite, sodium nitrite, acetic acid and sodium acetate – also increased the risk of developing type 2 diabetes. In this case the probability increased by 49%, according to the research.
A sixth preservative – calcium propionate – has also been linked. It is a white powder used to stop mold and bacteria growth.
In this type 2 diabetes study, more than two antioxidant supplements increased the risk. Additives that increased the risk by 42% included alpha-tocopherol, the most bioavailable form of vitamin E; sodium ascorbate, which is a buffered form of vitamin C and sodium; rosemary extracts; sodium erythorbate, obtained from fermented sugar; phosphoric acid, a preservative in juice, processed meats, cheeses, and other foods; and citric acid, a flavor enhancer, preservative and pH adjuster with no significant nutritional value.
Because these two studies are the first to examine the role of preservatives in the development of cancer and type 2 diabetes, much more research will be needed to confirm and extend the findings, said Anaïs Hasenböhler, the first author of both studies, who is a PhD candidate in the Nutrition Epidemiology Research Team at Sorbonne University Paris Nord.
However, Hasenböhler added in a statement: “These new data add to others in favor of a re-evaluation of the regulations governing the general use of food additives by the food industry to improve consumer protection.”
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