What’s the deal with nitrites and nitrates?

Recently, the French Agency for Food, Environmental, and Occupational Health & Safety (ANSES) dealt a blow to the French meat industry. And the ripples are likely to be felt further afield.

On July 12, 2022, they released a statement calling for people to limit their exposure to nitrates and nitrites. Manufacturers add these compounds to processed meats, such as ham, bacon, deli meat, and hot dogs. 

ANSES explain:

“Concerning nitrites, over half of our exposure is related to the consumption of delicatessen meat due to the nitrite additives used to prepare it.”

They recommend that people consume no more than 5.3 ounces (150 grams) of these processed meat products weekly.

The move comes following the growing evidence that nitrate and nitrite consumption is linked to colorectal cancer risk. 

French meat processors feared they might face an outright ban on the compounds. Instead, the government promised to reduce the amount of nitrites that these companies use.

Some politicians in the United Kingdom are also pushing meat manufacturers to phase out the use of nitrites.

Below, we explain these chemicals and why they appear to harm health.

What are nitrates and nitrites?

Nitrates and nitrites are preservatives formed from nitrogen and oxygen atoms. 

Food manufacturers add them to meat, along with salt, to give foods a longer shelf life and improve their taste and color.

These compounds also kill bacteria, such as Clostridium botulinum, which is responsible for botulism — a potentially life-threatening infection.

Nitrates occur naturally, particularly in leafy greens. However, they also enter the environment through intensive farming through fertilizers and sewage runoff. 

According to ANSES, around two-thirds of the nitrates we consume are from plants. About one-quarter is through drinking water, and just 4% comes from processed meats.

For nitrites, however, more than half of our dietary intake is consumed in meat products.

What happens to nitrates and nitrites in the body?

Nitrates are fairly stable, and nitrites readily react with oxygen to produce nitrates. So, once consumed, most nitrates and nitrites leave your body in urine as nitrate. 

However, bacteria in the mouth can convert nitrates into nitrites.

Some nitrites are converted into nitric oxide — a relatively harmless chemical that’s used widely in your body.

But once in the acidic environment of the stomach, nitrites can help produce nitrosamines. And some nitrosamines can cause cancer.

Having looked at the evidence, ANSES conclude that: 

Nitrates, nitrites, and cancer

Over the years, there has been much interest in the links between meat and cancer. 

There is now good evidence that processed meat increases the risk of bowel cancer. 

Scientists are still investigating what role nitrates and nitrites might play in this — other factors may also play a part.

For instance, cooking meat can produce other cancer-causing chemicals, such as heterocyclic aromatic amines and polycyclic aromatic hydrocarbons.

Also, heme iron, which is present in meat, may increase cancer risk. 

However, evidence is growing that nitrites and nitrates might be directly involved in the cancer risk linked to processed meats.

The evidence 

Below, we look at some of the most recent studies into cancer, nitrates, and nitrites:

Nitrites and cancer

Three recent reviews have examined the effect of nitrites on cancer. One review found that processed meat containing nitrites was linked to an increased risk of bowel cancer compared with non-processed meat. 

However, a more recent meta-analysis did not find this association. 

Another meta-analysis, which included data from 18 studies and more than 800,000 people, found that moderate or high intake of nitrites was linked to a higher risk of stomach cancer. 

Nitrates and cancer

Recent meta-analyses have found associations between nitrates and increased risks of bowel and ovarian cancers. 

A meta-analysis, published in 2021, looked at 15 studies involving more than 2.5 million participants aged 20–85.

The scientists concluded that dietary nitrate was linked to an increased risk of bowel cancer. In this study, however, dietary nitrite was not.

Another review, this time looking at diet and ovarian cancer, analyzed data from 97 studies. Again, the authors concluded that nitrates were associated with an increased risk.

Conversely, moderate or high intake of nitrates seemed to protect against stomach cancer. 

The authors believe this protective effect might be because a nitrate-rich diet usually includes a lot of plants. As we saw earlier, we consume around two-thirds of our nitrates in plants.

Vegetables and fruits often contain vitamin C and other antioxidants, and these nutrients block the production of cancer-causing nitrosamines.

This emphasizes one of the main challenges in nutrition science — no one eats chemicals one by one.

Instead, we eat foods containing hundreds or thousands of compounds, all of which might interact with each other to produce different effects in the body.

Splitting natural from added

The studies above all shared the same pitfall: They didn’t distinguish between the sources of nitrites and nitrates — whether they came from water, plants, or cured meat, for instance.

A large study from France, which used data from more than 101,000 participants, tried to address this knowledge gap. 

They compared the effects of added nitrates and nitrites, like those used to cure meat, and natural nitrates and nitrites, like those in vegetables.

They concluded that:

• Higher intakes of added nitrates were associated with higher breast cancer risk. 

• Higher intakes of added nitrites were associated with higher prostate cancer risk.

Although they didn’t find any links to colon cancer, the authors explain that there were too few cases to reach a solid conclusion.

The scientists didn’t find links between nitrites and nitrates from natural sources and cancer risk.

This is particularly interesting because the participants tended to consume much higher levels of natural nitrates and nitrites than they did added nitrates and nitrites.

Again, the scientists explain that this is probably because natural sources tend to be plants, which carry a range of other beneficial compounds that either counteract or reduce the negative effects of these compounds.

What should you do?

The links between processed meat and colon cancer are fairly well established.

However, the precise role of nitrates and nitrites is still being hammered out — but it seems that adding them to food might increase the risk of some cancers.

ZOE believes restrictive diets don’t work, so no foods are off the table. However, processed meats are associated with an increased risk of many health conditions. 

So, overall, it’s probably best to enjoy them just once in a while.