Is Sodium Nitrite (food additive e250) carcinogenic?

Question

Reading a recent news article about a Dutch fish processing firm using Sodium Nitrite for white fish processing I learned that the additive is associated with a higher risk of cancer when used in processing white fish. An English source states:

Sodium nitrite is cleared for use in meat products but is considered to be potentially cancer-causing when used with fish.

Source: Fish processing firm Foppen under fire for using banned products

Reading into why sodium nitrite would be harmful in combination with fish, but not with other foods, I couldn't find much except broader warnings against eating foods with e250, especially for pregnant women. E.g.:

Health effects are acute methemoglobinemia (haemoglobin loses its ability to carry oxygen). Early symptoms include irritability, lack of energy, headache, dizziness, vomiting, diaorrhea, laboured breathing and a blue-gray or pale purple colouration to areas around the eyes, mouth, lips, hands and feet (blue baby syndrome).

Source: UKFoodGuide

Or

Side effects/ Connected to; Irritability, lack of energy, headaches, dizziness. Pregnancy complications, Infant health problems; Linked with Leukaemia, many cancers such as colon, bladder, stomach, thyroid etc.

Wakingtimes (emphasis mine)

Are these warnings against eating anything with e250 scientifically justified, or is it all baloney (nudge nudge)? If so, why is it that it is banned for use in processing fish, but not meats?

Answer 1

There's good evidence for it.

"Red and processed meat consumption and risk of pancreatic cancer: meta-analysis of prospective studies" went over several related studies, including several focusing on nitrites. "Pancreatic Cancer and Drinking Water and Dietary Sources of Nitrate and Nitrite" states

Increasing intake of dietary nitrite from animal sources was associated with an elevated risk of pancreatic cancer among men and women (highest quartile odds ratios = 2.3, 95% confidence interval: 1.1, 5.1, for men and 3.2, 95% confidence interval: 1.6, 6.4, for women).

"Etiology of Pancreatic Cancer, With a Hypothesis Concerning the Role of N-Nitroso Compounds and Excess Gastric Acidity" also discussed this. "Meat and components of meat and the risk of bladder cancer in the NIH-AARP Diet and Health Study" studied this and found

These findings provided modest support for an increased risk of bladder cancer with total dietary nitrite and nitrate plus nitrite from processed meat. Results also suggested a positive association between red meat and PhIP and bladder carcinogenesis.

A very good overview is given here. It states

A critical report in the long-lasting nitrite debate was a 1970 paper by Lijinsky and Epstein (1970) titled “Nitrosamines as Environmental Carcinogens” published in Nature, which showed that nitrosamines were potent and specific carcinogenic compounds.

Nitrosamines are not the same thing as nitrites. However,

In foods, nitrosamines are produced from nitrites and secondary amines, which often occur in the form of proteins. Their formation can occur only under certain conditions, including strongly acidic conditions such as that of the human stomach.

"Relevance of nitrosamines to human cancer" is interesting, especially as it says,

Direct proof that such nitrosation reactions can occur was provided by Ender et al. (3) who identified NDMA in nitrite preserved fish-meal, and by Sander and Seif (4) who demonstrated the formation in vivo of a nitrosamine in the acidic conditions of the human stomach.

"NDMA", by the way, is N-nitrosodimethylamine.

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Are these warnings against eating anything with e250 scientifically justified, or is it all baloney (nudge nudge)?

No, it's not all baloney. There is serious evidence the nitrites can cause cancer. However, as a source I used before mentioned, studies have also shown that there are some benefits to nitrites. Admittedly, those don't nullify the cancer risk.

If so, why is it that it is banned for use in processing fish, but not meats?

I have no idea. Also, as an interesting aside, it's okay for fish in the United States.

Answer 2

This seems to be a good summary of recent research. http://www.atsdr.cdc.gov/csem/csem.asp?csem=28&po=10 Most of the page seems to point to nitrates as being bad for you.