Two new studies from France suggest that 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.
“These are very important findings for preservatives, which are widely used not only in the French and European markets, but also in the United States,” said senior author Mathilde Touvier, principal investigator of the NutriNet-Santé study, which conducted the study.
The NutriNet-Santé study began in 2009 and compared the diet and lifestyle network reports of more than 170,000 participants with medical data stored in France’s national health care system.
“These are two of the first studies in the world to investigate the relationship between exposure to these food additives and cancer and type 2 diabetes,” said Tourvel, who is also research director at the French National Institute of Health and Medical Research in Paris. “So we have to be very cautious about this information. Obviously, the results need to be confirmed.”
Despite these warnings, “concerns about preservatives are another reason why many people emphasize the importance of fresh, whole, minimally processed foods (mostly plants) to personal and public health,” Dr. David Katz said in an email.
Katz, who was not involved in the study, is a preventive and lifestyle medicine expert who founded the nonprofit Real Health Initiative, a global alliance of experts dedicated to evidence-based lifestyle medicine.
Cancer and preservatives
The cancer study was published Wednesday in british medical journal The journal looked closely at the effects of 58 preservatives on about 105,000 cancer patients in 2009 and followed them for 14 years. Only those who regularly completed the 24-hour brand-specific food questionnaire were included. Researchers compared people who ate the foods with the most preservatives to those who ate the least.
The researchers took an in-depth look at 17 preservatives consumed by at least 10 percent of the participants and found that 11 of them were not linked to cancer. However, the FDA considers six foods to be GRAS, or “generally recognized as safe,” linked to cancer. These include sodium nitrite, potassium nitrate, sorbate, potassium metabisulfite, acetate, and acetic acid.
Sodium nitrite, a chemical salt commonly used in processed meats such as bacon, ham and deli meats, has been linked to a 32% increased risk of prostate cancer. Its close relative, potassium nitrate, is associated with a 22% increased risk of breast cancer and a 13% increased risk of all cancers. The World Health Organization has long considered processed meat a carcinogen with direct links to colon cancer.
Sorbates, especially potassium sorbate, increase the risk of breast cancer by 26% and the risk of all types of cancer by 14%. These water-soluble salts are used in wine, baked goods, cheeses, and sauces to protect against mold, yeast, and some bacteria.
Studies show that potassium metabisulfite, commonly used in brewing and brewing, is associated with a 20% increased risk of breast cancer and an 11% increased risk of all cancers.
Acetate, which comes from natural fermentation and is used in foods such as meats, sauces, breads and cheeses, is associated with a 25% increase in breast cancer risk and a 15% increase in cancer risk. The study found that acetic acid, the main component of vinegar, was associated with a 12% increased risk of all cancers.
Other types of preservatives—antioxidants such as vitamin C and vitamin E, plant extracts such as rosemary, and synthetic preservatives such as butylated hydroxyanisole—have also been studied. While these more “natural” preservatives generally reduce cancer risk when consumed 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 effects on our health may be different depending on how our gut microbiome digests it,” she said.
Research has found that only two antioxidant preservatives are linked to cancer. Sodium erythorbate and other erythorbates, made from fermented sugars, are associated with a 21% increase in breast cancer and a 12% increase in overall cancer rates.
Erythorbic acid is used to prevent discoloration and spoilage in poultry, soft drinks, baked goods, etc. Sodium erythorbate is often used in processed meats to speed up the curing process.
Observational studies can be subject to error due to a lack of control over variables that may affect the results. However, the study’s main strength is its ability to adjust for natural sources of preservatives and other food additives, as well as “detailed assessment of preservative intake through repeated 24-hour dietary records,” according to an editorial accompanying the study.
“We also looked at publications by our colleagues on the effects of these preservative chemicals on animal models, cell models, gut microbiota, oxidative stress and inflammatory processes, which may explain what we observed,” Tourvel said.
In addition, Tourvel said, both studies controlled for confounding factors such as physical activity, smoking, alcohol consumption, drug use and lifestyle.
“The finding that specific classes of preservatives are associated with increased risk of specific cancers is robust to all of these adjustments and suggests that this is an issue that deserves respect and requires further study,” 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 type 2 diabetes at the start of the study.
The researchers examined 17 preservatives, 12 of which were linked to a nearly 50 percent increased risk of type 2 diabetes in those who ate the highest levels of preservatives.
Five of the same cancer-causing preservatives — potassium sorbate, potassium metabisulfite, sodium nitrite, acetic acid and sodium acetate — also increase the risk of type 2 diabetes. Research shows that in this case, the probability rises by 49%.
A sixth preservative—calcium propionate—is also involved. It is a white powder used to stop the growth of mold and bacteria.
In this study of type 2 diabetes, more than two antioxidant supplements were associated with an increased risk. Additives that increased the risk by 42 percent included alpha-tocopherol, the most bioavailable form of vitamin E; sodium ascorbate, which is a buffered form of vitamin C and sodium; rosemary extract; sodium erythorbate, which is made from fermented sugar; phosphoric acid, a preservative in soda, processed meats, cheese, 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 explore the role of preservatives in the development of cancer and type 2 diabetes, more research is needed to confirm and extend these findings, said first author Anaïs Hasenböhler, a doctoral student in the Nutritional Epidemiology Research Group at the University of Paris-Nord-Sorbonne.
However, Hasenböhler added in a statement that “these new data, combined with other data, facilitate a re-evaluation of regulations governing the general use of food additives in the food industry to improve consumer protection.”
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