Common food preservatives linked to cancer and type 2 diabetes

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(CNN) — 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 over 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 two first studies in the world investigating 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, “and so we must be very cautious about the message. Obviously, the results need to be confirmed.”

Despite those caveats, “the concern raised about preservatives is one more reason among many to emphasize the personal and public health importance of fresh, whole, minimally processed foods, mostly plants,” Dr. David Katz said in an email.

Katz, who was not involved in the study, is a specialist in preventive and lifestyle medicine 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 free of cancer in 2009 and were followed for up to 14 years. Only those who completed frequent 24-hour, brand-specific food questionnaires were included. People who ate the most preservative-laced food were compared with those who ate the least.

Researchers did a deep dive on 17 preservatives consumed by at least 10% of the participants and found 11 of those had no relationship with cancer. However, the six that were linked to cancer are considered GRAS, or “generally recognized as safe” in food by the US Food and Drug Administration. Those 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, 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 as 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 cancers. These water-soluble salts are used in wine, baked goods, cheeses and sauces to prevent molds, yeast and some bacteria.

Potassium metabisulfite, often used in winemaking and brewing, was associated with a 20% increase in breast cancer and 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, breads and cheese, were linked to a 25% higher risk of breast cancer and 15% increase in cancer in general. Acetic acid, the main ingredient in vinegar, was associated with a 12% increase in the risk of all cancers, the study found.

Other types of preservatives — antioxidants such as vitamin C, vitamin E, plant extracts like rosemary and such synthetic preservatives as butylated hydroxyanisole — were also studied. While these more “natural” preservatives are often linked to lower cancer risk when eaten as whole foods, they may be harmful when used as additives, Touvier said.

“The hypothesis here is when you isolate one substance from its original matrix of a 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 sugars, were associated with a 21% higher incidence of breast cancer and 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 might also influence outcomes. However, a major strength of this study was its ability to adjust for preservatives from natural sources and other food additives as well as its “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 on the impact of these preservative chemicals on animal models, cellular models, gut microbiota, oxidative stress and inflammatory processes which may explain what we observe,” Touvier said.

In addition, both studies controlled for such confounding factors as a physical activity, tobacco, alcohol use, medication use and lifestyle factors, Touvier said.

“The finding that specific classes of preservatives are associated with increased risk of select cancers was robust to all of these adjustments, indicating it is a matter that warrants respect and requires 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 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 with nearly a 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 raised the risk of developing type 2 diabetes. In this case the probability rose by 49%, according to the research.

A sixth preservative — calcium propionate — was also connected. It’s a white powder used to stop mold and bacterial growth.

In this study on type 2 diabetes, more than two antioxidant additives increased risk. Additives that increased 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 meats, cheeses 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 required to confirm and expand the findings, said Anaïs Hasenböhler, the first author of both studies who is a doctoral student at the Nutritional Epidemiology Research Team at the Université Sorbonne Paris Nord.

However, Hasenböhler added in a statement, “These new data add to others in favour 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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