Concerns about preservatives and cancer risk have circulated for decades, driven largely by laboratory studies showing that some additives can influence the formation of carcinogenic compounds or biological processes linked to cancer risk, such as oxidative stress and inflammation.

Yet, translating these mechanistic signals into real-world cancer risk has been challenging. 

Epidemiological evidence linking preservative additives to cancer risk remains limited, inconsistent, and often confounded by the foods that contain these additives — especially processed meats and alcohol — rather than the preservatives themselves. 

Take nitrites/nitrates — among the most studied preservatives in relation to cancer risk.

"Nitrites and nitrates could contribute to the increased risk, but nitrites and nitrates are consumed mainly through processed meats, which are considered carcinogenic," Edward Giovannucci, MD, ScD, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health in Boston, told Medscape Medical News. 

Some studies have also reported links between higher sulfite intake and cancer risk.

However, "sulfites are consumed predominantly from alcoholic beverages, and high alcohol is carcinogenic to humans, although other alcohol breakdown products (especially acetaldehyde) are known strong carcinogens, so likely are causing the increased risk," Giovannucci noted.

How Strong Is the Link?

Recent findings, published earlier this year in The BMJ, provide further insights into the possible link between food preservatives and cancer risk.

In the French NutriNet-Santé prospective cohort, multiple modest positive associations between intake of widely used preservative food additives and higher cancer incidence emerged.

Led by Mathilde Touvier, PhD, head of the nutritional epidemiology research team at the French National Institute for Health and Medical Research (INSERM), the study included 105,260 adults (mean age, 42 years, 79% women) who completed at least two 24-hour dietary recall records in their first 2 years of follow-up and did not have prevalent cancer. The study team linked repeated brand-specific dietary records to three food composition databases and laboratory assays, which is far more granular than most nutrition epidemiology. 

Of the 58 food additive preservatives consumed by participants, 17 were consumed by at least 10% of the study population, and researchers focused their analysis on these 17 preservatives. 

After an average follow-up of 7.5 years, 4226 (4.2%) participants developed cancer, most commonly breast, prostate, and colorectal cancer. Of the 17 individually studied preservatives, six showed statistical associations with cancer incidence, while 11 did not.

After adjusting for potential confounders, researchers observed a modestly increased risk for overall cancer among participants who consumed higher amounts of total non-antioxidant preservatives (hazard ratio [HR], 1.16), total sorbates (HR, 1.14), total sulfites (HR, 1.12), potassium metabisulfite (HR, 1.11), potassium nitrate (HR, 1.13), total acetic acid (HR, 1.12), and sodium erythorbate (HR, 1.12). 

As for specific cancers, the study showed an increased risk for breast cancer among participants with a higher intake of total non-antioxidants (HR, 1.22), total sorbates (HR, 1.26), potassium metabisulfite (HR, 1.12), potassium nitrate (HR, 1.22), total acetates (HR, 1.25), and sodium erythorbate (HR, 1.21). 

Higher intake of sodium nitrate was associated with increased risk for prostate cancer (HR, 1.32). There was a trend toward a positive association between colorectal cancer and nitrites (HR, 1.26) and nitrates (HR, 1.23) that did not reach statistical significance, likely due to the limited number of incident colorectal cancers. 

However, absolute risk differences were small. For instance, for total non-antioxidants, the estimated absolute risk for cancer at age 60 was 13.3% in higher consumers vs about 12% in lower consumers. Similarly, for both total sorbate and sulfites, the estimated absolute risk for cancer in this age group was 13.4% in higher consumers vs just under 12%.

So, how concerned should people be about consuming preservatives?

"For the most part, preservatives should not be of high concern at this point, though future monitoring of risk is warranted," Giovannucci told Medscape. 

"Given the modest increased risk estimates, causality cannot be established and unmeasured or residual confounding cannot be ruled out, especially considering the strong correlations between some preservatives and their food vectors," Giovannucci and a co-author explained in a BMJ editorial.

What to Tell Patients

Because preservatives are added ubiquitously by food manufacturers, they can be tough to avoid.

"What can be advised is, overall, to favor food and drinks that are less/minimally processed and look for alternatives when possible," said Anaïs Hasenböhler, PhD student on Touvier's team. Fresh and also frozen vegetables, for instance, contain fewer preservatives than refrigerated processed and ultra-processed ones, she noted. 

For most preservatives or foods high in preservatives, Giovannucci doesn't think the evidence is strong enough for recommendations to avoid. Plus, he noted, preservatives can offer benefits by extending shelf life, preventing foods from spoiling, and lowering food costs, which can be important for individuals with lower incomes.

There are exceptions. Highly processed meats should be avoided and alcohol limited or avoided. "These are clearly carcinogenic, though it is unclear how much of the risk is due to preservatives," Giovannucci said.  

Eleonora Teplinsky, MD, head of breast and gynecologic medical oncology at Valley-Mount Sinai Comprehensive Cancer Care in Paramus, New Jersey, often fields questions from patients about preservative food additives. 

While "it's important to validate their concerns, don't amplify the fear," she said. Instead, "reframe around, what can they do for their health that actually will make the difference." 

Teplinsky counsels patients not to fixate on avoiding individual preservatives but to focus on the dietary patterns associated with lower cancer risk, including limiting alcohol, eating fewer ultraprocessed foods and processed meats, and consuming more fresh fruits and vegetables.

Still, use of these additives is "widespread and often insufficiently monitored," Giovannucci and a co-author wrote in the BMJ editorial. Currently, the FDA evaluates the premarket safety of food additives but does not have a systematic post-market review framework for substances already in the food supply. 

Given uncertainties surrounding their long-term health effects, Giovannucci noted that regulatory agencies may consider "setting stricter limits on use, requiring clearer labeling, and mandating disclosure of additive contents." 

Hasenböhler, Giovannucci, and Teplinsky had no relevant disclosures.