Processed foods promise convenience, low cost and a long shelf life. What they rarely advertise is how many chemical preservatives it takes to keep a snack cake or microwavable meal stable for months.

There's another troubling trade-off: Higher intakes of several widely used food preservatives are linked to an increased risk of cancer.

The findings in the French research drew from one of the world's most detailed nutrition studies — the NutriNet-Santé cohort. Researchers followed over 105,000 people who were cancer-free when they enrolled between 2009 and 2023.

Sodium nitrate, widely used in processed meats like hotdogs, was linked to a 32 percent higher risk of prostate cancer.

Participants in the study, whose average age was 42, completed multiple, 24-hour, brand-specific dietary records. That allowed investigators to track not only what people ate, but exactly which packaged foods, and which additives, they consumed. Health questionnaires, medical records and national death registries were then used to identify cancer cases through December 31, 2023.

Participants were followed for an average of 7.5 years. During that time, 4,226 of those in the study developed cancer, including: 1,208 breast cancers; 508 prostate cancers; and 352 colorectal cancers.

The team examined 17 commonly used preservatives, among them sulfites, sodium nitrate, potassium sorbate, sodium potassium nitrate and citric acid. These were grouped into nonantioxidant preservatives, which inhibit microbial growth or spoilage, and antioxidant preservatives, which lower food deterioration by limiting oxygen.

It's important to note that not all additives were problematic. Eleven of the 17 preservatives were not associated with cancer, and total preservative intake was not linked to cancer overall. But when researchers looked at specific compounds, a different picture emerged.

Several non-antioxidant preservatives showed consistent association with cancer risk. For instance:

  • Potassium sorbate, commonly found in baked goods, cheese and soft drinks, was linked to a 14 percent higher risk of overall cancer and 26 percent higher risk of breast cancer among high consumers.
  • Sulfites were associated with a 12 percent increased risk of overall cancer.
  • Sodium nitrate, widely used in processed meats like hotdogs, was linked to a 32 percent higher risk of prostate cancer.
  • Potassium nitrate was associated with 13 percent higher risk of overall cancer risk and a 22 percent higher risk of breast cancer.
  • Total acetates and acetic acid were also associated with an increased risk of cancer overall and breast cancer in particular.

Why might preservatives matter? Research suggests that several of these compounds can alter immune and inflammatory pathways and can damage cells and DNA. These are biological effects that can promote cancer development. The authors caution that this was an observational study, meaning it cannot prove that preservatives directly cause cancer. Other, unmeasured factors may also play a role.

Preservatives are not all bad. They can extend shelf life, reduce food waste, and keep costs down — a benefit for families with limited resources.

Even so, the researchers say the evidence is strong enough to warrant concern. The study was unusually large, followed participants for more than a decade and used highly detailed food records linked to commercial product databases. The results were also consistent with laboratory findings suggesting cancer-related effects from several of these chemicals.

As the authors conclude, “This study brings new insights for the future re-evaluation of the safety of these food additives by health agencies, considering the balance between benefit and risk for food preservation and cancer.”

Preservatives are not all bad, as Harvard researchers point out in an editorial accompanying the study. Preservatives can extend shelf life, reduce food waste and keep costs down — a benefit for families with limited resources.

But the widespread and often insufficiently monitored use of preservatives, combined with uncertainty about their long-term health effects, calls for a more balanced approach. The editorial suggests stricter limits on preservatives, clearer labeling and mandatory disclosure of additive content, along with international monitoring such as has been done for trans fats and salt or sodium, would go a long way toward protecting the public.

For consumers, the message is not to panic, but to be selective. The more food is processed, the more likely it is to contain multiple preservatives. Favoring fresh or minimally processed foods — more fruits and vegetables, plain dairy, beans, eggs and unprocessed meats — can reduce exposure to the additives now under scrutiny, while still keeping meals affordable.

The study is published in the bmj.