Sodium nitrate
A preservative used in cured and processed meats to block bacterial growth and fix the pink colour. Converts to nitrite in the body.
Nitrate converts to nitrite in the body, which can form N-nitroso compounds linked to colorectal cancer. Regular processed-meat eating is classified as a cause of colorectal cancer by the WHO's cancer agency.
What is it?
Sodium nitrate is the sodium salt of nitric acid. It is a white crystalline solid that occurs naturally in soil and some vegetables. As a food additive it acts as a curing agent, supplying a reservoir of nitrate that bacteria and enzymes slowly convert to nitrite during meat curing.
What does it do?
In cured meat, sodium nitrate is reduced to sodium nitrite (E250) over time by bacteria and reducing agents. The nitrite then reacts with myoglobin to form stable pink nitrosomyoglobin, fixing the characteristic colour of bacon, ham and salami. It simultaneously inhibits the growth of Clostridium botulinum, the bacterium responsible for botulism, and suppresses fat oxidation that causes rancidity. Because it releases nitrite slowly, it is preferred for long-cured products where a sustained effect is needed.
Where you will see it
Cured hams, dry-cured and fermented meats such as salami and chorizo, long-aged bacons, and some cured fish products. On a UK label it appears as 'sodium nitrate', 'E251', or within a 'curing salts' mixture. It is sometimes listed alongside E250 (sodium nitrite).
What the science says
Processed meat and colorectal cancer: IARC Group 1
In 2015, the International Agency for Research on Cancer (IARC) classified the consumption of processed meat as a Group 1 carcinogen, meaning there is sufficient evidence it causes colorectal cancer in humans. The classification is based on the meat category, not on any single additive. Nitrate and nitrite added during curing are considered part of the mechanistic picture because they can form N-nitroso compounds in the gut.
IARC Working Group classified processed meat as Group 1 carcinogenic to humans, with colorectal cancer as the primary site. Every 50g portion of processed meat eaten daily was associated with approximately an 18% increase in colorectal cancer risk.
IARC Monographs Volume 94 classified ingested nitrate as Group 2A (probably carcinogenic to humans) under conditions that result in endogenous nitrosation, i.e. when nitrate leads to the formation of N-nitroso compounds in the body.
N-nitroso compound formation: the proposed mechanism
When nitrite (derived from ingested nitrate) meets amines and amides in the acidic environment of the stomach and colon, it can form N-nitroso compounds (NOC). Many NOCs are carcinogenic in animal studies. The presence of haem iron in red meat accelerates this endogenous nitrosation. The evidence links the combination of processed meat, nitrate/nitrite and haem rather than any single component acting alone.
Haem iron in red and processed meat catalyses the endogenous formation of N-nitroso compounds in the gut, providing a plausible mechanistic link between processed meat consumption and colorectal cancer.
In isolation, nitrate itself shows no or limited direct carcinogenic potential in animal bioassays; the cancer signal emerges when nitrate is converted to nitrite and then to NOCs in vivo.
NHS advice and processed meat limits
Following the IARC findings, the NHS and the Scientific Advisory Committee on Nutrition (SACN) recommended limiting processed red meat to no more than 70g a day. People who eat more than this are advised to cut down. The guidance applies to all processed meat, not specifically to nitrate-containing products, but nitrate-cured meats are the primary category in scope.
The NHS advises eating no more than 70g of processed meat per day and cutting down if intake is higher, citing the cancer link identified in population studies.
Methaemoglobinaemia in infants
High nitrate intake can convert haemoglobin to methaemoglobin, which cannot carry oxygen efficiently. Infants under six months are most vulnerable because foetal haemoglobin is more easily oxidised and gut bacteria that reduce nitrate to nitrite are more active in their digestive tract. This risk has historically been associated with high-nitrate well water rather than food additives used at regulated levels, but it establishes the biological hazard underpinning strict ADI limits.
Nitrate at high doses causes methaemoglobinaemia in infants, a condition that reduces oxygen transport. Regulatory maximum levels in food are set partly to protect this sensitive group.
EFSA 2017 re-evaluation and ADI
The European Food Safety Authority re-evaluated nitrates and nitrites as food additives in 2017. For nitrate (E251 and E252), EFSA set an acceptable daily intake of 3.7 milligrams per kilogram of bodyweight per day, expressed as nitrate ion. EFSA noted that some population groups, particularly children with high processed-meat consumption, may exceed this ADI. The FSA accepted the EFSA position and existing UK maximum levels were retained.
EFSA ANS Panel established an ADI of 3.7 mg/kg bodyweight per day for nitrate ion and found that exposure from food additive use is generally within the ADI for adults, but some children may exceed it.
Where it stands with the regulators
Who should be careful
People who eat processed meat regularly, particularly every day, carry the highest cumulative exposure. Infants under six months should not consume foods containing added nitrate. People with conditions affecting oxygen transport should discuss cured-meat intake with their doctor. Look for 'sodium nitrate', 'E251', or 'curing salts' on the label.
The honest read
The science on nitrate in food additives sits at two levels. At the additive level, sodium nitrate is approved and maximum levels are set below what EFSA considers harmful for most adults. At the dietary pattern level, the IARC Group 1 classification for processed meat as a whole is one of the more robust findings in nutrition epidemiology, supported by large pooled studies across multiple countries. The mechanism, endogenous formation of N-nitroso compounds from nitrite, haem iron and protein in the gut, is biologically plausible and reproduced in lab and animal work. The complication is that most people eating processed meat are eating the whole product, nitrate plus haem plus salt plus cooking chemistry, so isolating sodium nitrate's individual contribution to cancer risk is not possible from existing data. What is established is the association between the food category and the cancer outcome. The ongoing policy question, whether lower maximum permitted levels or alternative preservatives would reduce population risk, is actively researched and not resolved.
Related additives
Common questions
Is E251 banned in the UK?
No. Sodium nitrate (E251) is approved for use in the UK under assimilated EU Regulation 1333/2008, which the UK retained in law after Brexit. It is permitted in specific food categories including cured and processed meats, up to defined maximum levels.
Does sodium nitrate cause cancer?
The additive itself is classified by IARC as Group 2A (probably carcinogenic to humans) under conditions that lead to N-nitroso compound formation in the body. The food category it is most associated with, processed meat, is classified IARC Group 1, meaning there is sufficient evidence that regular consumption of processed meat causes colorectal cancer. The individual contribution of sodium nitrate versus other components of processed meat cannot be separated from existing studies.
What foods contain E251?
Cured and fermented meats are the primary source: dry-cured ham, salami, chorizo, pepperoni, long-cured bacon, and some cured fish. It may also appear in certain hard cheeses applied to the rind to inhibit mould. Check the label for 'sodium nitrate' or 'E251' in the ingredients.
Is E251 vegan?
Sodium nitrate as an ingredient is a mineral salt with no animal origin. However, the foods it is used in, primarily cured and processed meats, are not vegan. Vegans are unlikely to encounter it in their diet.
Sources
- IARC Monographs Volume 114: Red Meat and Processed Meat (2018 update of 2015 findings)
- Bouvard et al., Carcinogenicity of consumption of red and processed meat, Lancet Oncology
- IARC Monographs Volume 94: Ingested Nitrate and Nitrite, and Cyanobacterial Peptide Toxins
- EFSA ANS Panel, Re-evaluation of sodium and potassium nitrites and nitrates as food additives, EFSA Journal
- UK Food Standards Agency: Nitrates and Nitrites - The Science Explained
- UK Food Standards Agency: Approved Additives and E Numbers
- NHS: Red meat and bowel cancer
Aaron Keen is the founder of NutraSafe. He researches and writes every additive entry himself, from the primary sources. About the research →
This is a guide, not medical advice. If an additive affects you, speak to your GP or a dietitian.
See this on every food you scan
NutraSafe reads the label and puts every additive into plain English, with the source, right in the app.
Get NutraSafe on the App Store