A disturbing and tragic report came out in 1997 that chronicled the deaths of three cats in New Zealand. Upon necropsy, each of the cats’ blood had a brownish discoloration. This abnormal color suggested methemoglobinemia, which is due to nitrate or nitrite poisoning. The commercial cat foods they were eating were tested for nitrite, a preservative added to processed meats to combat bacterial growth and to preserve color. Turns out, the food had a mean concentration of 2850 mg of total nitrite per kg of food (as fed).
With the building interest in nitrate and nitrite concentrations in the environment and food, we wondered if any more recent surveys of pet food had occurred. We found five.
Before you ask, the European Union has set a nitrite threshold of 100 mg/kg for pet food with a water content greater than 20%. In the United States, the Association of American Feed Control Officials (AAFCO) has recommended a standard of ≤ 20 ppm or 20 mg/kg of food. Remember, that is simply a recommendation made by AAFCO. It has no regulatory enforcement.
Two researchers at Ankara University screened 50 different cat (25 imported, 25 local) and 50 different dog foods (25 imported, 25 local).
According to them, the safety level of nitrate for dogs is 2% through food consumption. Cats are more sensitive and should eat less nitrates and nitrites.
We are not sure how the 2% safety level was determined, but the authors do provide a reference to a textbook written in their native language.
They determined that the nitrate and nitrite concentrations in all imported and locally produced foods were below the threshold. They did note, however, that the nitrate and nitrite levels were higher in domestic cat foods.
The researchers purchased seventeen imported and domestic dog food samples that they classified as semi-dry (10-30% water), semi-moist (25-35% water), or wet (about 75% water) based on water content.
First of all, they found that imported dog food and wet dog food had higher nitrite concentrations than the other dog food samples.
They also investigated nitrite concentrations based on packaging. They found that canned food had the highest nitrite concentrations compared to dog food in plastic bags and pouches.
However, they ran into a problem: there were no nitrite health thresholds for dogs through food consumption in Japan at the time. So, they looked at human consumption as a basis and established two standard doses: daily intake and acceptable daily intake.
Daily intake is what you do. Acceptable daily intake is what you should do.
The researchers then adjusted these levels for dogs.
None of the dog food samples exceeded the standard dose determined from the daily intake. However, some samples did exceed the standard dose obtained from the acceptable daily intake.
10 imported wet pet foods were tested for nitrates and nitrites. Four pet food formulas came from Italy, 2 from Brazil, and one each from the United States, Germany, Czech Republic and Thailand.
The nitrate and nitrite contents of each of the foods greatly exceeded the recommended AAFCO level.
In 2013, an acceptable daily intake of nitrites by dogs through food was not established in Japan, as noted in the last Japanese study.
By 2015, this had changed. Japanese law capped nitrite levels found in pet foods at 100 ppm or 100 mg/kg. It looks as though this country decide upon a limit without much research.
Kobayashi and team contended with this in 2017.
They tested 33 imported and domestic wet cat foods.
They applied the allowable daily intake of sodium nitrite of 0.07 mg/kg of body weight for humans to cats, since no threshold existed for cats.
They provided an example of one pet food that needed adjustment for allowable daily intake.
Moisture content was 85% with a recommended daily portion of about 100 grams per kilogram of body weight.
0.07 mg/100 g=0.7 ppm
Moisture content is corrected to 10% to comply with the ingredient specifications of the law. The nitrite concentration that could remain in the cat food is:
0.7 ppm × (100 − 10)%/(100−85)% = 4.2 ppm
Based on this value, eight of the 33 samples they tested would exceed the concentration standard.
Furthermore, when converted into sodium nitrite:
4.2 × (molecular weight of sodium nitrite)/(molecular weight of the nitrite ion)=6.3 ppm
This value is much lower than the current legal regulation standard of less than 100 ppm.
In essence, regulations were met, but eight samples exceeded the allowable daily intake.
Abd-Elhakim, Yasmina M., et al. “An Investigation of Selected Chemical Contaminants in Commercial Pet Foods in Egypt.” Journal of Veterinary Diagnostic Investigation, vol. 28, no. 1, 11 Jan. 2016, pp. 70–75, doi:10.1177/1040638715624733, https://journals.sagepub.com/doi/full/10.1177/1040638715624733.
Becer, Ulku Kamile, and Ayhan Filazi. “Aflatoxins, Nitrates and Nitrites Analysis in Commercial Cat and Dog Foods.” Fresenius Environmental Bulletin, vol. 19, no. 11, 15 Apr. 2010, pp. 2523–2527, https://bit.ly/34izh7p.
Kobayashi, Jun, et al. “Factors Affecting Nitrite Concentrations in Cat Food.” Journal of Animal Research and Nutrition, vol. 02, no. 01, 5 June 2017, doi:10.21767/2572-5459.100028, https://bit.ly/2WwaU3i.
Kobayashi, Jun, et al. “Nitrite Concentrations in Commercial Dog Foods.” Journal of Veterinary Science & Technology, vol. 7, no. 5, 5 Aug. 2016, doi:10.4172/2157-7579.1000369, https://bit.ly/2C2TSAt.
Worth, A.J., et al. “Nitrite Poisoning in Cats and Dogs Fed a Commercial Pet Food.” New Zealand Veterinary Journal, vol. 45, no. 5, 1997, pp. 193–195, doi:10.1080/00480169.1997.36025, https://www.tandfonline.com/doi/abs/10.1080/00480169.1997.36025.