IARC (International Agency for Research on Cancer) is sometimes very quick to nominate any chemical as at least a probable carcinogen. And so it is with nitrate and nitrite. Pointing to the endogenous nitrogen cycle in humans (that is ingested nitrate recirculated in saliva and converted to nitrite by microorganisms in the mouth and swallowed) IARC concluded that both nitrate and nitrite are probable human carcinogens as they can generate carcinogenic N-nitroso compounds under acidic gastric conditions.
Now let’s make it clear, EFSA in two recently published opinions on nitrate and nitrite partially supported the IARC conclusions on the link between nitrates and nitrites in processed meat and an increased risk of colorectal cancer. But, and this is a big BUT….
Both additives are considered safe to use at current approved levels without any concerns. So why is that?
Nitrate and nitrite cleared as additive at current levels
EFSA, in contrast to IARC, not only looks at the potential for a substance to cause cancer, but also the exposure level necessary. That is practical life conditions. And concluded that existing safe levels for nitrates and nitrites intentionally added to meat and other foods are sufficiently protective for consumers.
Case closed? Well, not so fast. Let’s look at some of the detail.
EFSA’s Panel on Food Additives and Nutrient Sources Added to Food said that there is some evidence in epidemiological studies of a link between dietary nitrite, preformed N-nitroso compounds and gastric cancers and also for the combination of nitrate plus nitrite from processed meat and colorectal cancers. However, they stressed that this included only very limited evidence.
Using refined exposure assessment scenarios, the Panel calculated that exposure to nitrites as a food additive accounts for 17% of total exposure to nitrite and exposure to nitrates as a food additive only accounts for up to 5% of total exposure to nitrates. Other sources making up the balance of exposure include their natural presence in other food products and environmental contamination.
The main contributors to exposure are vegetables and vegetable-based foods, such as starchy roots, leafy vegetables, such as spinach and lettuce, and prepared salads. Nitrates also contaminate water as a result of intensive farming, fertilisers and sewage discharge.
The remaining problem
Although the use of nitrate and nitrite as additives have little influence on overall exposure, there is still a remaining overall concern.
If all sources of dietary nitrate are considered, such as food additive use, natural presence in food and environmental contaminants, the Acceptable Daily Intake may be exceeded for individuals of all age groups with medium to high exposure.
If all sources of dietary nitrite are considered, the Acceptable Daily Intake may be exceeded for infants, toddlers and children with average exposure, and for highly exposed individuals of all age groups.
However, the estimated formation in the body of N-nitroso compounds from nitrites added to food items at the approved level were far below those that could be considered to be of risk to human health.
To further reduce uncertainties, the Panel made several recommendations, including:
- additional studies to measure the excretion of nitrate into human saliva, its conversion to nitrites, and the resulting methaemoglobin formation (a potential problem in babies);
- further studies on the levels of N-nitroso compounds formed in different meat products based on known amounts of added nitrites/nitrates;
- large-scale epidemiological studies on nitrite, nitrate and nitrosamine intake and risk of certain cancer types.
In the meantime an Acceptable Daily Intake of 0.07 mg/kg body weight for nitrite and 3.7 mg/kg body weight for nitrate as food additives would be of no concern as most people would not exceed it through eating food to which the additives had been added and only some children would slightly exceed nitrite additive exposure.