Maternal diet and risk of astrocytic glioma in children: a report from the Childrens Cancer Group (United States and Canada)

Childhood cancer in relation to cured meat intake: review of the epidemiological evidence

Over the past two decades a series of epidemiological studies have examined the relationship between consumption of cured meats during pregnancy and the subsequent risk of brain tumors, as well as other cancers, in the offspring. The research was prompted in large part by experimental investigations showing that transplacental exposure to certain N-nitroso compounds, i.e., nitrosoureas, could produce brain tumors in laboratory animals. Fourteen such epidemiological studies, 13 of which used the case-control approach, are reviewed here. Most of the studies showed no significant association between total cured meat intake and childhood cancer risk but more found positive than negative relationships. Furthermore, several studies reported significant positive associations for maternal and sometimes childhood or paternal consumption of one or more cured meats, with odds ratios of twofold or greater reported among the highest consumers. On the other hand, a correlation analysis found no positive concordance between temporal trends from the 1970s to 1990s in childhood brain cancer rates and cured meat consumption, inasmuch as cancer rates rose over time while residual nitrite levels in cured meats fell sharply. Because of the potential for bias, especially recall bias, and/or confounding, the relatively weak magnitude of the associations reported, and the inconsistency between study findings, at this time it cannot be concluded that eating cured meat has increased the risk of childhood brain cancer or any other cancers. Moreover, although N-nitroso compounds are sometimes found in cured meats or may be formed endogenously, there is no empirical evidence that eating cured meats results in human neural nitrosourea exposure. Nevertheless, the hypothesis that eating nitrite-cured meats may influence childhood and perhaps adult brain cancer cannot be dismissed. Unbiased evaluation of the hypothesis may derive from the conduct of cohort studies, where the interview-derived information on cured meat intake precedes, or is not otherwise associated with, the diagnosis of cancer.

Influence of turkey meat on residual nitrite in cured meat products

A response surface experimental design was employed to estimate residual nitrite level at various initial nitrite concentrations, percent turkey meat in the formula, and heat quantity (F) values using a typical wiener as the test system. Pork and mechanically separated turkey were used as the meat ingredients. Residual nitrite and pH were measured at day 1, 7 days, 14 days, and 49 days after processing. Protein, fat, salt, moisture, and CIE (L*a*b*) color values were also determined. Results showed that the effect of turkey meat on residual nitrite level was significant (P < 0.01). An increased amount of turkey meat in the formula resulted in lower residual nitrite levels at a fixed pH. The residual nitrite level was initially proportional to initial nitrite concentration, but it became a nonsignificant factor during longer storage time. Differences in heat quantity had a significant effect (P < 0.05) on residual nitrite level initially. Greater heat quantity decreased residual nitrite level in finished cured meat products at a fixed pH. However, this effect became nonsignificant during longer storage. Reduction of residual nitrite in wieners because of turkey meat addition at a fixed pH was due to characteristics of the turkey tissue, but the mechanism of action remains unknown. It was also established that commercial wieners had a higher pH if poultry meat was included in the formulation.

Childhood brain tumours and exposure to animals and farm life: a review

Brain tumours are the most common solid tumour in children. However, little is known about their aetiology, and only a small percentage of cases can be attributed to established risk factors. Exposure to farm animals and pets have been considered as possible risk factors for childhood brain tumour (CBT) development for several reasons. Numerous factors associated with farm life, including bacteria, pesticides, solvents and some animal oncogenic viruses, have been found to induce brain tumour formation in animals. Some studies have found viral gene sequences in human brain tumours. Epidemiological studies of brain tumours in adults have reported an increased risk among veterinarians and farmers. In this review, data are examined from seven case-control studies published between 1979 and 1998 that considered a possible relationship between fetal or childhood exposure to farm animals or pets and CBT. Five of the seven studies examined childhood farm residence or exposure of mother or child to farm animals and, of these five, four reported elevated risk for CBT with odds ratios (OR) ranging from 0.9 to 2.5 for maternal exposures and from 0.6 to 6.7 for children's exposures. Later studies that were larger subsequently examined histological type and reported excess risk for primitive neuroectodermal tumours (PNETs) with farm residence prenatally (OR = 3.7, CI = 0.8, 24) or in childhood (OR = 5.0, CI = 1.1, 4.7). Increased risk of PNET was also associated with maternal exposure to pigs (OR = 12, CI = .1, 47) or poultry (OR = 4.0, CI = 1.2, 13). The results of these studies showed few other consistent relationships between farm life or farm animals and CBT.

The role of nutritional habits during gestation and child life in pediatric brain tumor etiology

Our aim was to evaluate the role of maternal nutritional habits during the period of gestation and of children subsequent diet in the etiology of pediatric brain tumors. All cases of incident nervous system tumors under age 18, diagnosed between 1984 and 1993 (n = 300) in Israel were identified. Two matched population controls per case were selected (n = 574). Personal interviews, using a semi-quantified three-step food frequency questionnaire, were performed. Univariate analysis showed that increased child consumption of vegetable fat [p trend 0.01; 95% confidence interval (CI) 1.1-3.2], carbohydrates (p trend 0.05; CI 1.0-5.9), and vitamin E (p trend 0.05; CI 1.0-3.3), were significantly associated with brain tumor risk. No associations were found with nitrate, nitrite or vitamin C. A significant positive association with potassium consumption (p trend 0.01; CI 1.1-3.7) was noted during gestation. Results of multivariate analysis showed that the only persisting associations were with vegetable fat (OR = 1.36; CI 1.06-1.73) in the child diet and potassium intake during gestation (OR = 1.44; CI 1.04-1.99). In conclusion, nutritional associations with pediatric brain tumor etiology, remain unsubstantiated.

Cancer surveillance series [corrected]: brain and other central nervous system cancers: recent trends in incidence and mortality

BACKGROUND

During the 1980s, the incidence of primary malignant brain and other central nervous system tumors (hereafter called brain cancer) was reported to be increasing among all age groups in the United States, while mortality was declining for persons younger than 65 years. We analyzed these data to provide updates on incidence and mortality trends for brain cancer in the United States and to examine these patterns in search of their causes.

METHODS

Data on incidence, overall and according to histology and anatomic site, and on relative survival were obtained from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute for 1975 through 1995. Mortality data were obtained from the National Center for Health Statistics. Medicare procedure claims from the National Cancer Institute's SEER-Medicare database were used for imaging trends. Statistically significant changes in incidence trends were identified, and annual percent changes were computed for log linear models.

RESULTS/CONCLUSIONS

Rates stabilized for all age groups during the most recent period for which SEER data were available, except for the group containing individuals 85 years of age or older. Mortality trends continued to decline for the younger age groups, and the steep increases in mortality seen in the past for the elderly slowed substantially. Patterns differed by age group according to the site and grade of tumors between younger and older patients. During the last decade, use of computed tomography scans was relatively stable for those 65-74 years old but increased among those 85 years old or older.

IMPLICATIONS

Improvements in diagnosis and changes in the diagnosis and treatment of elderly patients provide likely explanations for the observed patterns in brain cancer trends.

Dietary nitrates, nitrites, and N-nitroso compounds and cancer risk: a review of the epidemiologic evidence

Experimental animal studies have shown N-nitroso compounds (NOC) to be potent carcinogens. Epidemiologic evidence of the carcinogenic potential of dietary NOC and precursor nitrates and nitrites in humans remains inconclusive with regard to the risk of stomach, brain, esophageal, and nasopharyngeal cancers. Inadequate available data could obscure a small to moderate effect of NOC.

Induction of hepatic and renal P4502E1 of neonatal rats exposed translactationally to ethanol

The effect of maternal ethanol intake during lactation on neonatal cytochrome P4502E1 was investigated in Sprague-Dawley rats. Dams were exposed to 15% (v/v) ethanol in drinking water from day 1 of lactation to 4, 7 or 14 days postpartum. Significant (P < 0.01) enhancement of both hepatic and renal N-nitrosodimethylamine (NDMA) demethylase, an activity of P4502E1, was observed in lactating mothers given ethanol in drinking water. Demethylase activity also significantly increased (P < 0.01) in the 7- and 14-day livers of both female and male pups and in the 7- and 14-day female and 14-day male kidneys exposed to ethanol through the transmammary route. Cytochrome P4502E1 protein content, assayed by immunoblotting, increased in the maternal liver and kidney of all groups consuming ethanol. Neonatal P4502E1 protein content increased in the 7- and 14-day livers of both sexes and 14-day female kidneys exposed translactationally to ethanol. No effect of ethanol on enzyme activity or protein content of P4502E1 was observed in the liver or kidney of 4-day-old neonates. These results demonstrate the translactational effect of ethanol on neonatal P4502E1 enzyme, which is involved in the metabolism of many low molecular weight xenobiotics, and indicate the possibility of alterations occurring in the kinetics of neonatal drug and xenobiotic metabolism and also in processes connected with perinatal carcinogenesis.

Evaluation of hamburgers and hot dogs for the presence of mutagens

Food products derived from heat-treated (fried, broiled, baked) meat may contain traces of mutagenic heterocyclic amine contaminants, some of which are proven carcinogens in rodents. To confirm their presence and range in Canadian foods, and estimate the average human intake of these types of mutagens from frequently consumed heat-processed foods, several commercially prepared fried-beef patties (hamburgers) and hot dogs (weiners) were analysed for their mutagenic capacity. The mutagenicity of the extracts was tested in the Salmonella/microsome assay using strain TA98 with metabolic activation. 16 samples of hamburgers and 14 samples of hot dogs, randomly obtained from 'fast food' commercial establishments or street vendors, were used in this survey. The mutagenic activity of these samples ranged from very low to 1042 revertants/g equivalent for the hamburgers and from non-detectable to 4875 revertants/g equivalent for the hot dogs. The average values were 199 and 424 revertants/g for the hamburgers and hot dogs, respectively. The wide range in mutagenicity was found even for the same type of product obtained from the same outlet at different times. This indicates possible inconsistency in cooking procedures during the preparation of these products. It also shows the difficulty in accurately assessing the intake of mutagenic heterocyclic amines from hamburgers and hot dogs prepared in 'fast food' outlets.

What is the etiology of human brain tumors? A report on the first Lebow conference

Although the conference could not provide a definitive etiologic explanation for the observed increase in incidence of human brain tumors, particularly among the elderly, nevertheless, this interdisciplinary gathering of prominent scientists and clinicians proved invaluable in identifying new avenues of research. Clearly, the puzzle of what causes brain tumors is highly complex, involving links to ionizing/electromagnetic radiation, familial, and dietary factors. The Lebow Conference provided an important scientific framework upon which to build further research studies, and its influence will be felt for years to come.

Role of N-nitroso compounds (NOC) and N-nitrosation in etiology of gastric, esophageal, nasopharyngeal and bladder cancer and contribution to cancer of known exposures to NOC

The questions of whether and how N-nitroso compounds (NOC) may be inducing cancer in humans are discussed. The principal subjects covered include nitrite-derived alkylating agents that are not NOC, reasons for the wide tissue specificity of carcinogenesis by NOC, the acute toxicity of nitrosamines in humans, mechanisms of in vivo formation of NOC by chemical and bacterial nitrosation in the stomach and via nitric oxide (NO) formation during inflammation, studies on nitrite esters, use of the nitrosoproline test to follow human gastric nitrosation, correlations of nitrate in food and water with in vivo nitrosation and the inhibition of gastric nitrosation by vitamin C and polyphenols. Evidence that specific cancers are caused by NOC is reviewed for cancer of the stomach, esophagus, nasopharynx, urinary bladder in bilharzia and colon. I review the occurrence of nitrosamines in tobacco products, nitrite-cured meat (which might be linked with childhood leukemia and brain cancer) and other foods, and in drugs and industrial situations. Finally, I discuss clues from mutations in ras and p53 genes in human tumors about whether NOC are etiologic agents and draw some general conclusions.

The role of chemical, physical, or viral exposures and health factors in neurocarcinogenesis: implications for epidemiologic studies of brain tumors

This review highlights some future prospects and implications for epidemiologic research on the etiology of nervous system tumors. It reviews some points regarding physiology of the nervous system, in connection with mechanisms of neurocarcinogenesis, and experimental studies in animals. The results of epidemiologic studies are summarized in the light of the biological and experimental observations. The following aspects are particularly emphasized: (i) higher susceptibility of the developing nervous system to neurocarcinogenic agents (in the fetus and after birth); (ii) possible implications of knowledge about mechanisms of neurocarcinogenesis regarding crossing of the blood-brain barrier, activation of oncogenes and inactivation of anti-oncogenes, relationship between chemical structure and neurocarcinogenic action; (iii) necessity of further investigation concerning the occurrence of nitrosoureas and their precursors in the environment, and the potential role of nitroso compounds in the development of human brain tumors; (iv) lack of information about promoting or inhibiting neurocarcinogenic effects, and co-carcinogenesis--among others, interaction between X-irradiation and exposure to neurocarcinogenic nitrosoureas; (v) need for studying the potential neurocarcinogenic risk of polyomaviruses BKV, JCV, and SV40 to humans.

Cured and broiled meat consumption in relation to childhood cancer: Denver, Colorado (United States)

The association between cured and broiled meat consumption by the mother during pregnancy and by the child was examined in relation to childhood cancer. Five meat groups (ham, bacon, or sausage; hot dogs; hamburgers; bologna, pastrami, corned beef, salami, or lunch meat; charcoal broiled foods) were assessed. Exposures among 234 cancer cases (including 56 acute lymphocytic leukemia [ALL], 45 brain tumor) and 206 controls selected by random-digit dialing in the Denver, Colorado (United States) standard metropolitan statistical area were compared, with adjustment for confounders. Maternal hot-dog consumption of one or more times per week was associated with childhood brain tumors (odds ratio [OR] = 2.3, 95 percent confidence interval [CI] = 1.0-5.4). Among children, eating hamburgers one or more times per week was associated with risk of ALL (OR = 2.0, CI = 0.9-4.6) and eating hot dogs one or more times per week was associated with brain tumors (OR = 2.1, CI = 0.7-6.1). Among children, the combination of no vitamins and eating meats was associated more strongly with both ALL and brain cancer than either no vitamins or meat consumption alone, producing ORs of two to seven. The results linking hot dogs and brain tumors (replicating an earlier study) and the apparent synergism between no vitamins and meat consumption suggest a possible adverse effect of dietary nitrites and nitrosamines.

Processed meats and risk of childhood leukemia (California, USA)

The relation between the intake of certain food items thought to be precursors or inhibitors of N-nitroso compounds (NOC) and risk of leukemia was investigated in a case-control study among children from birth to age 10 years in Los Angeles County, California (United States). Cases were ascertained through a population-based tumor registry from 1980 to 1987. Controls were drawn from friends and by random-digit dialing. Interviews were obtained from 232 cases and 232 controls. Food items of principal interest were: breakfast meats (bacon, sausage, ham); luncheon meats (salami, pastrami, lunch meat, corned beef, bologna); hot dogs; oranges and orange juice; and grapefruit and grapefruit juice. We also asked about intake of apples and apple juice, regular and charcoal broiled meats, milk, coffee, and coke or cola drinks. Usual consumption frequencies were determined for both parents and the child. When the risks were adjusted for each other and other risk factors, the only persistent significant associations were for children's intake of hot dogs (odds ratio [OR] = 9.5, 95 percent confidence interval [CI] = 1.6-57.6 for 12 or more hot dogs per month, trend P = 0.01), and fathers' intake of hot dogs (OR = 11.0, CI = 1.2-98.7 for highest intake category, trend P = 0.01). There was no evidence that fruit intake provided protection. While these results are compatible with the experimental animal literature and the hypothesis that human NOC intake is associated with leukemia risk, given potential biases in the data, further study of this hypothesis with more focused and comprehensive epidemiologic studies is warranted.

Diet and serum markers in relation to primary brain tumor risk in China

Associations between primary brain tumor mortality and dietary habits, certain serum biochemical markers, and life-style factors were evaluated in a county-based correlation study utilizing data collected from an ecological survey in 49 Chinese rural counties. Univariate correlation and multivariate regression analyses showed that high consumption of salt-preserved vegetables was linked to increased primary brain tumor mortality rates, although the association was significant only among men. In addition, high intake of green vegetables among men was associated with decreased rates. No clear association was seen between primary brain tumor mortality rates and tobacco use, body mass index, and serum biochemical markers. Limitations of these ecological data preclude causal inferences, but the findings provide etiologic clues to primary brain tumor mortality in rural China.