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 from France.
“These are very important findings for preservatives that are not only widely used in the French and European markets, but also in the United States,” said senior author Mathilde Touvier, principal investigator of the NutriNet-Santé study used to conduct the research.
The NutriNet-Santé study, which began in 2009, compares 170,000 participants’ web-based reports on diet and lifestyle 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 France’s National Institute of Health and Medical Research in Paris, “so we have to be very cautious about the message. Obviously, the results need to be confirmed.”
Despite those causes, “the concern raised about preservatives is one more reason among many to emphasize the personal and public health importance of fresh, whole, minimally processed, mostly 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 nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.
Cancer and preservatives
The cancer study, published Wednesday in The BMJ journal, closely examined the impact of 58 preservatives on some 105,000 people who were cancer-free in 2009 and were followed for up to 14 years. Only those who completed 24-hour food frequency and brand-specific questionnaires were included. People who ate the most foods laced with preservatives were compared to those who ate the least.
The researchers took a deep look at 17 preservatives consumed by at least 10% of the participants and found that 11 of those had no relation 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. Those include sodium nitrate, 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, was associated with a 32% increase in the risk of prostate cancer. It’s 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, were associated with a 26% higher risk for breast cancer and a 14% increase in all types of cancer. These water-soluble salts are used in wine, baked goods, cheese and sauces to prevent mold, yeast and some bacteria.
Potassium metabisulfite, often used in the production of wine and beer, 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. The study found that acetic acid, the main ingredient in vinegar, was associated with a 12% increase in the risk of all cancers.
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 when you isolate one substance from its original matrix of whole fruit or vegetable, the action on our health can be different depending on the way our gut microbiota will digest it,” she said.
Only two antioxidant preservatives were linked to cancer, the study found. Sodium erythorbate and other erythorbates, which are made from fermented sugar, were 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 baked goods, 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 may also influence the results. However, a major strength of this study was its ability to adjust for preservatives from natural sources and other food additives as well as “a detailed assessment of preservative consumption, 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, cellular models, gut microbiota, oxidative stress and inflammatory processes that could explain what we observe,” said Touvier.
In addition, both studies controlled for confounding factors such as physical activity, tobacco, alcohol use, medication use and lifestyle factors, Touvier said.
“The finding that specific classes of preservatives are associated with an increased risk of selected cancers was robust to all these adjustments, indicating that it is an issue that warrants respect and requires further research,” said Katz.
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 of the NutriNet-Santé participants who did not have the disease at the start of the study.
Twelve of the 17 preservatives researchers examined were linked to a nearly 50% 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 – was also implicated. It is a white powder used to stop the growth of mold and bacteria.
In this type 2 diabetes study, more than two antioxidant additives 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, made from fermented sugar; phosphoric acid, a preservative in sodas, processed meat, cheese and other foods; and citric acid, a flavor enhancer, preservative and pH adjuster with no significant nutritional value.
Since 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 expand the findings, said Anaïs Hasenböhler, first author of both studies who is a doctoral student in the Nutritional Epidemiology Research Team at Sorbonne University Paris Nord.
However, Hasenböhler added in a statement, “These new data add to others in favor of a reassessment of the regulations governing the general use of food additives by the food industry in order to improve consumer protection.”
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