Published on-line in the prestigious Proceedings of the National Academy of Sciences, the researchers report that the compounds, also found in vegetables and drinking water, reduced heart cell death in the mice following a heart attack by 48 per cent.
Animals with a low nitrite/nitrate diet had 59 per cent greater injury, report the researchers from the University of Texas Health Science Center at Houston.
Nitrites are added to meat to retard rancidity, stabilise flavour, and establish the characteristic pink colour of cured meat. Studies and recommendations by health and governmental organisations ensure the safety of such products.
However, observational studies, including data from the third National Health and Nutritional Examination Survey (NHANES) on 7,352 subjects over the age of 45, have suggested that increased consumption of nitrites from cured meat could increase the risk of lung disease.
"The public perception is that nitrite/nitrate are carcinogens but they are not," said lead author Nathan Bryan.
"Many studies implicating nitrite and nitrate in cancer are based on very weak epidemiological data. If nitrite and nitrate were harmful to us, then we would not be advised to eat green leafy vegetables or swallow our own saliva, which is enriched in nitrate."
He also notes that vegetables have up to 100 times more nitrate than processed meats, meaning nitrite and nitrate from processed or cured meats may account for only a small quantity of these compounds consumed in the diet.
The new study offers some positive news for the additives, reporting that mice fed an extra helping of nitrite had a survival rate of 77 per cent compared to 58 per cent for the mice that were nitrite deficient.
The mice were supplemented with nitrite (50 mg per litre of drinking water) for seven days. A comparison group received no nitrite supplementation. The researchers subsequently simulated a heart attack by stopping blood flow to the animals' hearts for 30 minutes, followed by 24 hours of reperfusion.
"This new appreciation of the health benefits of nitrite and nitrate is ironic," said co-author David Lefer, from Albert Einstein College of Medicine of Yeshiva University.
"They've traditionally been regarded as toxic because they tend to form chemicals called nitrosamines, some of which are carcinogenic. But recent research has found no convincing evidence that nitrite and nitrate pose a cancer risk."
"Simple changes in our daily dietary habits such as eating nitrite and nitrate rich foods such as fruits and vegetables and some meats in moderation can drastically improve outcome following a heart attack," added Bryan.
Significant further research is necessary, particularly to investigate if such observations occur in humans. The next logical step, said Bryan, could be to test if supplemental nitrite/nitrate in the diet can decrease the incidence and severity of heart attack and stroke in patients with known cardiovascular risk factors.
The potential mechanism behind the observations is proposed to be from the formation of nitric oxide from nitrites. Nitric oxide (NO) is a molecule used by the endothelium (cells lining the surface of blood vessels) to signal surrounding muscle to relax, leading to a reduction in blood pressure, reduced blood clotting and protection against myocardial infarction and strokes.
Commenting on the study, Ferid Murad, the 1998 Nobel Laureate for Physiology or Medicine said: "Interestingly, formulations of topical nitrite preparations are effective in wound and burn healing. Clinical trials for such uses as well as diabetic skin ulcers are also underway. It appears that dietary supplementation of nitrites and their topical uses will be effective and inexpensive therapies due to their conversion to nitric oxide."
Nitrite salts (also known as sodium nitrite) have traditionally been used to cure cooked meat products and fine paste sausages. However labelling of these salts as E250 is now negatively perceived by consumers, meaning that a clean label (non-E-number) alterative could be welcomed by industry and consumers.
Coupled with the concerns over lung health, ingredient suppliers now offer alternatives to the meat industry. Only recently, Danisco launched two new cultures that it says can give meats the same colour, flavour and shelf-life as those cured with nitrite salts - but allowing for all-natural claims to be made on the label.
Source: Proceedings of the National Academy of Sciences
Published on-line ahead of print, 12 November 2007
"Effects of dietary nitrite and nitrate on myocardial ischemia/reperfusion injury" Authors: N.S. Bryan, J.W. Calvert, J.W. Elrod, S. Gundewar, S.Y. Ji, D.J. Lefer