Since N-nitroso compounds (NOCs) were found to be potent experimental carcinogens more than 20 years ago, a succession of epidemiological studies has investigated the hypothesis that exposure to preformed NOCs or their precursors can cause brain tumors in humans . The results of a meta-analysis of seven case-control studies suggest that maternal consumption of cured meat during pregnancy may be a risk factor for childhood brain tumors, especially astrocytomas . An earlier review of the same studies, however, noted that some were based on rather small numbers of cases, the dietary information was apparently not validated, and selection bias could not be ruled out . A pooled analysis of nine studies of adults did not show clear evidence for an elevated risk of brain tumors with ingestion of NOCs from cured meat in adulthood . There is limited evidence for a reduction in risk of CNS tumors with increased fruit and vegetable consumption and with use of vitamin supplements, although studies have not been consistent . These results may support the N-nitroso hypothesis insofar as these nutrients inhibit the endogenous formation of nitrosamines, but any protective effect could be due to other mechanisms .
Tobacco smoke is a potent source of NOCs and polycyclic aromatic hydrocarbons (PAHs), among other carcinogens. Meta-analyses have provided little evidence of an association between maternal smoking during pregnancy and childhood brain tumors [20, 21]. Preconception and childhood exposure to paternal tobacco smoke revealed a raised risk, but confounding with other risk factors could not be ruled out . The results of studies of smoking as a risk factor for CNS tumors in adults have been inconsistent . Likewise, there is no consistent evidence for an elevated risk associated with alcohol consumption .
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