Ten questions & answers concerning nitrates and nitrites
What is the difference between nitrates and nitrites? Why are they found in food? Through what foods are we most exposed to these substances? Are we too exposed to them? Is there really such a thing as “nitrite-free” delicatessen meat? You will find all the answers to these questions in this article.
1. What are nitrates and why are they found in food?
Nitrates are natural components of plants that are essential for their growth.
The presence of nitrates in water resources and soil is due to:
- natural processes associated with the nitrogen cycle;
- agricultural activities such as the spreading of nitrogen fertilisers and livestock manure;
- urban and industrial waste (water very high in nitrates discharged from slaughterhouses and dairies, the chemical and pharmaceutical industries, and the paper industry).
Because they are contained in water, soil and plants, nitrates can end up in our food. They can also be intentionally added to delicatessen meat and certain cheeses in the form of food additives (E251 and E252), which account for less than 4% of our total exposure to nitrates, all sources combined.
2. What are nitrites and why are they found in food?
Nitrites result from nitrogen being naturally oxidised by microorganisms contained in plants, soil and water. They are also food additives used to prevent pathogenic bacteria such as Salmonella and Listeria monocytogenes from developing and also to keep toxins such as that responsible for botulism from being produced.
Most of the nitrites in our diet are found in delicatessen meat, added intentionally by manufacturers in the form of food additives (E249, E250). Exposure to nitrites as food additives accounts for around half of our total exposure to these substances.
Nitrates can also be converted into nitrites, both in food and in the human body following ingestion, under the action of oral bacteria.
Lastly, small amounts of nitrites can also be naturally found in fresh meat.
3. What are nitroso compounds?
Once nitrates and nitrites contained in water and food have been ingested, unstable compounds can form in the food and in the body. Known as nitroso compounds, these include nitrosamines, nitrosothiols, and nitrosylated haem iron. Some of these nitroso compounds are known for their genotoxicity and carcinogenicity.
4. Why are nitrates and nitrites used as food additives?
These substances are used as food additives for several reasons. The primary objective is to keep the number of bacteria from increasing during the various stages of the production process. Thanks to their antimicrobial properties, they are able to limit the growth of pathogenic bacteria responsible for foodborne infections such as salmonellosis, listeriosis and botulism. By doing so, they help extend the shelf life of products (i.e. they act as preservatives).
Lastly, additives in products can also maintain, enhance or impart taste and colour: for example, without these additives, cooked ham would be grey, not pink.
5. Through what foods are we most exposed to nitrates and nitrites?
Food accounts for 75% of our exposure to nitrates (80% for children) and drinking water accounts for the other 25% (20% for children). In our diet, vegetables – primarily leafy vegetables – contribute the most to nitrate exposure, with levels of 62% for adults and 69% for children.
Concerning nitrites, 99% of our exposure comes from food, in particular delicatessen meat, whether artisanal or industrial. Water accounts for less than 1% of our exposure to nitrites.
6. Are we too exposed to nitrates and nitrites?
To guarantee consumer safety, acceptable daily intakes (ADIs) are used by the health authorities. The ADI is the amount of a substance that an individual should be able to ingest every day without any risk to their health.
For nitrates and nitrites, the European Food Safety Authority (EFSA) has recommended one specific ADI for nitrates and another for nitrites. In its expert appraisal, the Agency notes that:
- For nitrates, less than 1.5% of adults and children exceed the ADI;
- For nitrites, less than 0.4% of children exceed the ADI and no adults exceed it.
The current ADIs have been defined separately for each of these substances. To take risks related to co-exposure into account, ANSES used an “MOE” (assessment of margins of exposure) approach in its expert appraisal. This led to similar results to those obtained by analysing the ADIs for the large majority of the population. An overall approach is needed that would include co-exposure to nitrates, nitrites and nitroso compounds and would take into account conversion mechanisms.
7. Is there really such a thing as “nitrite-free” delicatessen meat?
This depends on the meat in question: today, certain products such as dry-cured ham can be produced without nitrites. For other products, such as cooked ham and dry sausages, nitrites are more widely used to guarantee their safety over time and give them their characteristic colour.
8. Are “no nitrite added” products always a good alternative?
Some manufacturers add plant extracts or vegetable broths to delicatessen meat to replace nitrates and nitrites used as food additives. These extracts or broths can then become a source of natural nitrates, which are in turn converted into nitrites by the bacterial enzymes contained in them.
By buying these products, which can use the claim “no nitrites added”, consumers nevertheless continue to be exposed to nitrites and the associated risks.
9. Is delicatessen meat carcinogenic and if so, how?
The International Agency for Research on Cancer (IARC) classified the consumption of delicatessen meat as carcinogenic in 2018. Consumption of red meat was classified as probably carcinogenic to humans based on the presence of haem iron, an intrinsic component of red meat.
10. How can individuals reduce their exposure to nitrates and nitrites?
To limit their exposure, individuals are advised to reduce their consumption of delicatessen meat and red meat. This consumption should not exceed:
- 150g per week for delicatessen meat (i.e. the equivalent of around three slices of ham);
- 500g per week for red meat (excluding poultry).
Vegetables contain vitamins and minerals that are essential for the proper functioning of the body. Therefore, it is important to continue eating a wide variety of them while diversifying the sources of supply.