Intakes of nitrates and nitrites from processed meats, fruit and vegetables do not increase the incidence of brain tumours, says a new study from Imperial College London and Harvard.
The results challenge the hypothesis that the nitrogen-containing compounds may indirectly increase the risk of brain tumours, due to their contribution to the production of nitrosamine compounds, according to data published in the American Journal of Clinical Nutrition.
The results are also inline with other recent findings that the additives do not increase the risk of other cancers, with some studies reporting they should even be classed as ‘nutritious’.
About 80 per cent of nitrates in the diet come from vegetables, while nitrites sources include vegetables, fruit, and processed meats. 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 new study however found no such link between the much maligned additives in processed and cured meats and brain tumours, or glioma.
According to the American Brain Tumor Association, gliomas are tumours that start in the supportive tissue brain. The prognosis for people with this type of tumour is usually very poor.
According to background information in the new study, it has been hypothesised that nitrosamine exposure may increase the risk of glioma. However, effectively testing the link has been hampered by the ubiquitous nature of nitrosamine exposure, said the researchers.
Since nitrosamines are formed in the body from nitrate and nitrites, the researchers, led by Dominique Michaud from UCL, examined the effect of diet on glioma risk.
Data from three American prospective cohort studies were combined, giving a total of 335 glioma cases and a follow-up period of about 24 years. Intakes of nitrate and nitrite, and subsequent nitrosamine formation, were calculated using published values of these nutrients in various foods.
No increases in the risk of glioma were observed for people with highest intake of total processed meats, nitrate, nitrites or nitrosamine, compared to people with the lowest intakes of these.
“We found no suggestion that intake of meat, nitrate, nitrite, or nitrosamines is related to the risk of glioma,” concluded the researchers.
Source: American Journal of Clinical Nutrition
September 2009, Volume 90, Issue 3, Pages 570-577
"Prospective study of meat intake and dietary nitrates, nitrites, and nitrosamines and risk of adult glioma"
Authors: D.S. Michaud, C.N. Holick, T.T. Batchelor, E. Giovannucci, D.J. Hunter