Mothers' active and passive smoking during pregnancy and risk of brain tumours in children

Maternal smoking, consumption of alcohol, and caffeinated beverages during pregnancy and the risk of childhood brain tumors: a meta-analysis of observational studies

BACKGROUND

We conducted this meta-analysis to investigate the potential association between maternal smoking, alcohol and caffeinated beverages consumption during pregnancy and the risk of childhood brain tumors (CBTs).

METHODS

A thorough search was carried out on PubMed, Embase, Web of Science, Cochrane Library, and China National Knowledge Internet to identify pertinent articles. Fixed or random effects model was applied to meta-analyze the data.

RESULTS

The results suggested a borderline statistically significant increased risk of CBTs associated with maternal smoking during pregnancy (OR 1.04, 95% CI 0.99-1.09). We found that passive smoking (OR 1.12, 95% CI 1.03-1.20), rather than active smoking (OR 1.00, 95% CI 0.93-1.07), led to an increased risk of CBTs. The results suggested a higher risk in 0-1 year old children (OR 1.21, 95% CI 0.94-1.56), followed by 0-4 years old children (OR 1.12, 95% CI 0.97-1.28) and 5-9 years old children (OR 1.11, 95% CI 0.95-1.29). This meta-analysis found no significant association between maternal alcohol consumption during pregnancy and CBTs risk (OR 1.00, 95% CI 0.80-1.24). An increased risk of CBTs was found to be associated with maternal consumption of caffeinated beverages (OR 1.16, 95% CI 1.07-1.26) during pregnancy, especially coffee (OR 1.18, 95% CI 1.00-1.38).

CONCLUSIONS

Maternal passive smoking, consumption of caffeinated beverages during pregnancy should be considered as risk factors for CBTs, especially glioma. More prospective cohort studies are warranted to provide a higher level of evidence.

Risk factors for childhood brain tumours: A systematic review and meta-analysis of observational studies from 1976 to 2022

BACKGROUND

Childhood brain tumours (CBTs) are the leading cause of cancer death in children under the age of 20 years globally. Though the aetiology of CBT remains poorly understood, it is thought to be multifactorial. We aimed to synthesize potential risk factors for CBT to inform primary prevention.

METHODS

We conducted a systematic review and meta-analysis of epidemiological studies indexed in the PubMed, Web of Science, and Embase databases from the start of those resources through 27 July 2023. We included data from case-control or cohort studies that reported effect estimates for each risk factor around the time of conception, during pregnancy and/or during post-natal period. Random effects meta-analysis was used to estimate summary effect sizes (ES) and 95% confidence intervals (CIs). We also quantified heterogeneity (I2) across studies.

FINDINGS

A total of 4040 studies were identified, of which 181 studies (85 case-control and 96 cohort studies) met our criteria for inclusion. Of all eligible studies, 50% (n = 91) were conducted in Europe, 32% (n = 57) in North America, 9% (n = 16) in Australia, 8% (n = 15) in Asia, 1% (n = 2) in South America, and none in Africa. We found associations for some modifiable risk factors including childhood domestic exposures to insecticides (ES 1.44, 95% CI 1.20-1.73) and herbicides (ES 2.38, 95% CI 1.31-4.33). Maternal domestic exposure to insecticides (ES 1.45, 95% CI 1.09-1.94), maternal consumption of cured meat (ES 1.51, 95% CI 1.05-2.17) and coffee ≥ 2 cups/day (ES 1.45, 95% 95% CI 1.07-1.95) during pregnancy, and maternal exposure to benzene (ES 2.22; 95% CI 1.01-4.88) before conception were associated with CBTs in case-control studies. Also, paternal occupational exposure to pesticides (ES 1.48, 95% CI 1.23-1.77) and benzene (ES 1.74, 95% CI 1.10-2.76) before conception and during pregnancy were associated in case-control studies and in combined analysis. On the other hand, assisted reproductive technology (ART) (ES 1.32, 95% CI 1.05-1.67), caesarean section (CS) (ES 1.12, 95% CI 1.01-1.25), paternal occupational exposure to paint before conception (ES 1.56, 95% CI 1.02-2.40) and maternal smoking > 10 cigarettes per day during pregnancy (ES 1.18, 95% CI 1.00-1.40) were associated with CBT in cohort studies. Maternal intake of vitamins and folic acid during pregnancy was inversely associated in cohort studies. Hormonal/infertility treatment, breastfeeding, child day-care attendance, maternal exposure to electric heated waterbed, tea and alcohol consumption during pregnancy were among those not associated with CBT in both case-control and cohort studies.

CONCLUSION

Our results should be interpreted with caution, especially as most associations between risk factors and CBT were discordant between cohort and case-control studies. At present, it is premature for any CBT to define specific primary prevention guidelines.

Air pollution from industrial waste gas emissions is associated with cancer incidences in Shanghai, China

Outdoor air pollution may be associated with cancer risk at different sites. This study sought to investigate outdoor air pollution from waste gas emission effects on multiple cancer incidences in a retrospective population-based study in Shanghai, China. Trends in cancer incidence for males and females and trends in waste gas emissions for the total waste gas, industrial waste gas, other waste gas, SO₂, and soot were investigated between 1983 and 2010 in Shanghai, China. Regression models after adjusting for confounding variables were constructed to estimate associations between waste gas emissions and multiple cancer incidences in the whole group and stratified by sex, Engel coefficient, life expectancy, and number of doctors per 10,000 populations to further explore whether changes of waste gas emissions were associated with multiple cancer incidences. More than 550,000 new cancer patients were enrolled and reviewed. Upward trends in multiple cancer incidences for males and females and in waste gas emissions were observed from 1983 to 2010 in Shanghai, China. Waste gas emissions came mainly from industrial waste gas. Waste gas emissions was significantly positively associated with cancer incidence of salivary gland, small intestine, colorectal, anus, gallbladder, thoracic organs, connective and soft tissue, prostate, kidney, bladder, thyroid, non-Hodgkin's lymphoma, lymphatic leukemia, myeloid leukemia, and other unspecified sites (all p < 0.05). Negative association between waste gas emissions and the esophagus cancer incidence was observed (p < 0.05). The results of the whole group were basically consistent with the results of the stratified analysis. The results from this retrospective population-based study suggest ambient air pollution from waste gas emissions was associated with multiple cancer incidences.

Maternal Smoking and the Risk of Cancer in Early Life - A Meta-Analysis

BACKGROUND

In spite of the well-known harmful effects on the fetus, many women continue smoking during pregnancy. Smoking as an important source of toxic chemicals may contribute to the developmental origin of diseases.

OBJECTIVES

The aim of this work was to pursue the possible association between maternal smoking and cancer in early life. Specifically, we wanted to identify the associated early life cancer types, and to quantify the associations.

METHODS

In a systematic literature search 825 articles were identified in PubMed and Web of Science, and 55 more through the reference lists. Of these 62 fulfilled the criteria for inclusion in meta-analyses. Using Mantel-Haenszel or DerSimonian and Laird method, depending on heterogeneity of the studies, pooled estimates and 95% confidence intervals for eight cancer types were calculated.

RESULTS

Smoking during pregnancy was associated with an increased risk for for brain and central nervous system tumors (OR = 1.09; 95% CI = 1.02-1.17). Although the risk for lymphoma was also associated (OR = 1.21; 95% CI = 1.05-1.34), it did not hold up in subgroup analyses. Leukemia was not found to be associated with maternal smoking. Five other cancer types (bone, soft tissue, renal, hepatic, and germ cell cancer) were also examined, but the number of studies was too limited to exclude the possibility of maternal smoking as a risk factor for cancer in offspring.

CONCLUSIONS

According to our meta-analyses, maternal smoking is associated with nervous system cancers, but not with leukemia in early life. Confirming or rejecting associations of maternal smoking with lymphoma and the five other cancer types requires further studies.

A multinational case-control study on childhood brain tumours, anthropogenic factors, birth characteristics and prenatal exposures: A validation of interview data

Little is known about the aetiology of childhood brain tumours. We investigated anthropometric factors (birth weight, length, maternal age), birth characteristics (e.g. vacuum extraction, preterm delivery, birth order) and exposures during pregnancy (e.g. maternal: smoking, working, dietary supplement intake) in relation to risk of brain tumour diagnosis among 7-19 year olds. The multinational case-control study in Denmark, Sweden, Norway and Switzerland (CEFALO) included interviews with 352 (participation rate=83.2%) eligible cases and 646 (71.1%) population-based controls. Interview data were complemented with data from birth registries and validated by assessing agreement (Cohen's Kappa). We used conditional logistic regression models matched on age, sex and geographical region (adjusted for maternal age and parental education) to explore associations between birth factors and childhood brain tumour risk. Agreement between interview and birth registry data ranged from moderate (Kappa=0.54; worked during pregnancy) to almost perfect (Kappa=0.98; birth weight). Neither anthropogenic factors nor birth characteristics were associated with childhood brain tumour risk. Maternal vitamin intake during pregnancy was indicative of a protective effect (OR 0.75, 95%-CI: 0.56-1.01). No association was seen for maternal smoking during pregnancy or working during pregnancy. We found little evidence that the considered birth factors were related to brain tumour risk among children and adolescents.

Parental smoking and risk of childhood brain tumors by functional polymorphisms in polycyclic aromatic hydrocarbon metabolism genes

BACKGROUND

A recent meta-analysis suggested an association between exposure to paternal smoking during pregnancy and childhood brain tumor risk, but no studies have evaluated whether this association differs by polymorphisms in genes that metabolize tobacco-smoke chemicals.

METHODS

We assessed 9 functional polymorphisms in 6 genes that affect the metabolism of polycyclic aromatic hydrocarbons (PAH) to evaluate potential interactions with parental smoking during pregnancy in a population-based case-control study of childhood brain tumors. Cases (N = 202) were ≤10 years old, diagnosed from 1984-1991 and identified in three Surveillance, Epidemiology, and End Results (SEER) registries in the western U.S. Controls in the same regions (N = 286) were frequency matched by age, sex, and study center. DNA for genotyping was obtained from archived newborn dried blood spots.

RESULTS

We found positive interaction odds ratios (ORs) for both maternal and paternal smoking during pregnancy, EPHX1 H139R, and childhood brain tumors (P(interaction) = 0.02; 0.10), such that children with the high-risk (greater PAH activation) genotype were at a higher risk of brain tumors relative to children with the low-risk genotype when exposed to tobacco smoke during pregnancy. A dose-response pattern for paternal smoking was observed among children with the EPHX1 H139R high-risk genotype only (OR(no exposure) = 1.0; OR(≤3 hours/day) = 1.32, 95% CI: 0.52-3.34; OR(>3 hours/day )= 3.18, 95% CI: 0.92-11.0; P(trend )= 0.07).

CONCLUSION

Parental smoking during pregnancy may be a risk factor for childhood brain tumors among genetically susceptible children who more rapidly activate PAH in tobacco smoke.

Prenatal cadmium exposure alters postnatal immune cell development and function

Cadmium (Cd) is generally found in low concentrations in the environment due to its widespread and continual use, however, its concentration in some foods and cigarette smoke is high. Although evidence demonstrates that adult exposure to Cd causes changes in the immune system, there are limited reports of immunomodulatory effects of prenatal exposure to Cd. This study was designed to investigate the effects of prenatal exposure to Cd on the immune system of the offspring. Pregnant C57Bl/6 mice were exposed to an environmentally relevant dose of CdCl(2) (10ppm) and the effects on the immune system of the offspring were assessed at two time points following birth (2 and 7weeks of age). Thymocyte and splenocyte phenotypes were analyzed by flow cytometry. Prenatal Cd exposure did not affect thymocyte populations at 2 and 7weeks of age. In the spleen, the only significant effect on phenotype was a decrease in the number of macrophages in male offspring at both time points. Analysis of cytokine production by stimulated splenocytes demonstrated that prenatal Cd exposure decreased IL-2 and IL-4 production by cells from female offspring at 2weeks of age. At 7weeks of age, splenocyte IL-2 production was decreased in Cd-exposed males while IFN-γ production was decreased from both male and female Cd-exposed offspring. The ability of the Cd-exposed offspring to respond to immunization with a S. pneumoniae vaccine expressing T-dependent and T-independent streptococcal antigens showed marked increases in the levels of both T-dependent and T-independent serum antibody levels compared to control animals. CD4(+)FoxP3(+)CD25(+) (nTreg) cell percentages were increased in the spleen and thymus in all Cd-exposed offspring except in the female spleen where a decrease was seen. CD8(+)CD223(+) T cells were markedly decreased in the spleens in all offspring at 7weeks of age. These findings suggest that even very low levels of Cd exposure during gestation can result in long term detrimental effects on the immune system of the offspring and these effects are to some extent sex-specific.

[The Fetal Tobacco Syndrome - A statement of the Austrian Societies for General- and Family Medicine (ÖGAM), Gynecology and Obstetrics (ÖGGG), Hygiene, Microbiology and Preventive Medicine (ÖGHMP), Pediatrics and Adolescence Medicine (ÖGKJ) as well as Pneumology (ÖGP)]

Over more than 50 years, the nocuous effects of smoking in pregnancy on the fetus are well known. In the first years of science the focus was primarily on restricted fetal growth while in more recent years over 10.000 studies investigated the incomparably big sum of detrimental effects for the unborn's health. In this statement we want to present the recent scientific findings on this topic. The statement is aimed to show all doctors who treat pregnant women the present situation and evidence. In the beginning we give a short overview about the epidemiological situation in Europe. Then we present step by step the health effects with regards to pathophysiology and clinics. Furthermore the reader will learn about possibilities for smoking cessation in pregnancy. The problem of passive-smoking in pregnancy will be dealt with in a separate chapter. At present there is strong evidence that pregnant smoking has a detrimental effect on birth-weight, placenta-associated disease, stillbirth, sudden infant death syndrome (SIDS), childhood overweight, clefts, lung function, asthma, cardiovascular diseases and mental developmental disorders. These factors can be summarized by the term Fetal Tobacco Syndrome. There is supply for more studies for less investigated health effects. Pregnancy is a chance to stop smoking as most women show a high motivation in this period. Hence doctors of all disciplines should inform pregnant women about the detrimental effects of smoking on their unborn child and show them possibilities for smoking cessation.

Environmental toxicants and the developing immune system: a missing link in the global battle against infectious disease?

There is now compelling evidence that developmental exposure to chemicals from our environment contributes to disease later in life, with animal models supporting this concept in reproductive, metabolic, and neurodegenerative diseases. In contrast, data regarding how developmental exposures impact the susceptibility of the immune system to functional alterations later in life are surprisingly scant. Given that the immune system forms an integrated network that detects and destroys invading pathogens and cancer cells, it provides the body's first line of defense. Thus, the consequences of early life exposures that reduce immune function are profound. This review summarizes available data for pollutants such as cigarette smoke and dioxin-like compounds, which consistently support the idea that developmental exposures critically impact the immune system. These findings suggest that exposure to common chemicals from our daily environment represent overlooked contributors to the fact that infectious diseases remain among the top five causes of death worldwide.

Early life insult from cigarette smoke may be predictive of chronic diseases later in life

Evidence is rapidly accumulating that links cigarette smoke (CS) exposure in utero with the development of a variety of disease pathologies in the older offspring including, type 2 diabetes, obesity, certain childhood cancers and respiratory disorders. The role that the fetal environment plays in these late-onset outcomes and the underlying cellular/molecular mechanisms by which these CS-induced effects may occur are currently unknown. Although we are becoming more aware of the fact that prenatal insult can underlie childhood/adult diseases, critical knowledge gaps still exist including gene-environment interactions, and how a CS-induced imbalance in immune dynamics (i.e. TH1/TH2) might affect asthma development and/or exacerbation later in life. In this mini-review we introduce the concept of sexual dimorphism in CS-induced late-onset disease outcomes, as well as explore the mechanisms by which CS exposure in utero can lead to cardiovascular, cancer and respiratory abnormalities in the exposed offspring. By addressing such questions using animal models, appropriate intervention strategies can be developed that will help to protect children's health and their long-term quality of life.

An international case-control study of maternal diet during pregnancy and childhood brain tumor risk: a histology-specific analysis by food group

PURPOSE

Maternal dietary data from an international collaborative case-control study on childhood brain tumors were used to evaluate associations between histology-specific risk and consumption of specific food groups during pregnancy.

METHODS

Nine study centers from seven countries contributed 1218 cases and 2223 controls. Most cases were diagnosed between 1982 and 1992 and ranged in age from 0 to 19 years. Dietary consumption was measured as average grams per day.

RESULTS

Foods generally associated with increased risk were cured meats, eggs/dairy, and oil products; foods generally associated with decreased risk were yellow-orange vegetables, fresh fish, and grains. The cured meat association was specific to astrocytomas (odds ratio [OR] range=1.8-2.5 across astrocytoma subtypes for 4th vs. 1st quartile of consumption, p trends <or= 0.03) and ependymomas (OR, 2.0; 95% confidence interval (CI), 0.4-2.9 for 4th vs. 1(st) quartile; p trend=0.03) and was similar in magnitude to previously reported ORs relating maternal cured meat consumption to increased astroglial risk. Other histology-specific associations were decreased risk of anaplastic astrocytomas from cruciferous vegetables (OR, 0.4; 95% CI, 0.3-0.7 for 4th vs. 1st quartile; p trend<0.0001), decreased risk of astroglial tumors from fresh fish (OR, 0.6; 95% CI, 0.5-0.9 for 4th vs. 1st quartile; p trend=0.008), and increased risk of medulloblastoma from oil products (OR, 1.5; 95% CI, 1.0-2.2 for 4th vs. 1(st) quartile; p trend=0.005).

CONCLUSIONS

These results suggest the need for dietary analysis not only by brain tumor histology, but also by specific foods within a broad food group.

Immunotoxicity—The Risk is Real

Several papers published over the last year represent significant progress in closing the gap between rodent immunotoxicity data and human risk and indicate that, at least for the developing immune system, the concern raised by rodent data is justified. The studies reviewed here show that suppression of immune responses in rodents is predictive of suppression of immune responses in humans and that there is a relationship between immune suppression following developmental exposure to the toxicants and enhanced risk of infectious or neoplastic disease in humans. The three cases highlighted here are remarkable in that they all deal with real-world environmental exposures that represent different media -- air (cigarette smoke), water (arsenic), and food (polychlorinated biphenyls [PCBs]) -- and constitute very real risks. Moreover, the arsenic and PCB studies actually demonstrate a quantitative relationship between human exposure and immune suppression. There is evidence that in utero exposure to cigarette smoke and arsenic but not PCBs is associated with increased risk of allergic disease as well. There is clearly potential for designing studies that could address both issues.

Levels of 1-hydroxypyrene and other monohydroxy polycyclic aromatic hydrocarbons in children: A study based on U.S. reference range values

Urine samples collected in 1999 and 2000 as part of the National Health and Nutrition Examination Survey (NHANES) were analyzed for 14 monohydroxy polycyclic aromatic hydrocarbons (PAH, metabolites of 7 PAH compounds) and for the first time reference range values were calculated for these metabolites in the U.S. population. The purpose of this paper is to explore differences in these PAH metabolites between children (6-11 years old), adolescents, and adults. More than 99% of the urine samples contained a detectable amount of 1-hydroxypyrene (1-OHpyrene), a metabolite of pyrene. We found that children in the youngest age group (6-11 years) had a geometric mean level (creatinine corrected data) 30% higher than children and adults in the other age groups, but no statistical differences existed between the two genders and among different racial groups. Smokers and persons exposed to environmental tobacco smoke (ETS) in 12-19-year-old group and the 20-year-and-older group had higher levels of urinary 1-OHpyrene by a factor of 2-3 than non-smokers in the corresponding age group. Measurements of 3-hydroxyphenanthrene also suggested increased levels in children and in smokers. These results may indicate that young children are at a greater risk for PAH exposure, or that they absorb, distribute, metabolize, or eliminate PAH differently than adults.

Maternal medication use and the risk of brain tumors in the offspring: the SEARCH international case-control study

N-nitroso compounds (NOC) have been associated with carcinogenesis in a wide range of species, including humans. There is strong experimental data showing that nitrosamides (R(1)NNO.COR(2)), a type of NOC, are potent neuro-carcinogens when administered transplacentally. Some medications are a concentrated source of amides or amines, which in the presence of nitrites under normal acidic conditions of the stomach can form NOC. Therefore, these compounds, when ingested by women during pregnancy, may be important risk factors for tumors of the central nervous system in the offspring. The aim of the present study was to test the association between maternal use of medications that contain nitrosatable amines or amides and risk of primary childhood brain tumors (CBT). A case-control study was conducted, which included 1,218 cases and 2,223 population controls, recruited from 9 centers across North America, Europe and Australia. Analysis was conducted for all participants combined, by tumor type (astroglial, primitive neuroectodermal tumors and other glioma), and by age at diagnosis (< or =5 years; >5 years). There were no significant associations between maternal intake of medication containing nitrosatable amines or amides and CBT, for all participants combined and after stratification by age at diagnosis and histological subtype. This is the largest case-control study of CBT and maternal medications to date. Our data provide little support for an association between maternal use of medications that may form NOC and subsequent development of CBT in the offspring.

Effects of Prenatal Exposure to Cigarette Smoke on Offspring Tumor Susceptibility and Associated Immune Mechanisms

Epidemiologic evidence suggests that prenatal exposure to intact (unfractionated) cigarette smoke (CS) increases the incidence of cancer in the offspring. A toxicology study was carried out to examine the effects and underlying mechanisms of prenatal exposure to mainstream cigarette smoke (MCS) on offspring resistance to tumor challenge and surveillance mechanisms critical for the recognition and destruction of tumors. Pregnant B6C3F1 mice were exposed by inhalation to MCS for 5 days/week (4 h/day from gestational day 4 to parturition). Smoke-induced effects on offspring-host resistance to transplanted tumor cells; natural killer (NK) cell and cytotoxic T-lymphocyte (CTL) activity; cytokine levels; lymphoid organ immune cell subpopulations; and histology-were examined in 5-, 10- and 20-week-old male and female offspring. At a concentration of smoke roughly equivalent to smoking <1 pack of cigarettes/day, prenatally exposed male offspring challenged at 5 week of age with EL4 lymphoma cells demonstrated a greater than two-fold increase in tumor incidence (relative to age-/gender-matched air-exposed offspring); tumors in prenatally smoke-exposed pups also grew significantly faster. Cytotoxic T-lymphocyte activity in the smoke-exposed 5- and 10-week-old male pups was significantly less than that of the age- and gender-matched controls. No effects of prenatal CS exposure were observed on offspring NK activity, cytokine levels, lymphoid organ histology, or immune cell subpopulations. Results demonstrated that exposure of pregnant mice to a relevant dose of MCS decreased offspring resistance against transplanted tumor cells and persistently reduced CTL activity in prenatally exposed pups. This study provides biological plausibility for the epidemiologic data indicating that children of mothers who smoke during pregnancy have a greater risk of developing cancer in later life.

Maternal smoking during pregnancy and risk of brain tumors in the offspring. A prospective study of 1.4 million Swedish births

OBJECTIVE

Studies of the effect of maternal smoking during pregnancy on development of brain tumors in the offspring generally have found no increase in risk but most have mainly relied on retrospective exposure assessment. We conducted a prospective study on a large birth cohort in Sweden.

METHODS

Women giving birth during 1983-1997 were classified as smokers or non-smokers based on information ascertained at the first prenatal visit and recorded in the Swedish Birth Register. Follow-up of brain tumor incidence among offspring through 1997 was achieved by linkage with the Swedish Cancer Register. Hazard ratios were estimated using Cox proportional hazard regression, adjusting for demographic characteristics available in the Birth Register.

RESULTS

Brain tumors (n=480) occurred at a rate of 4.5 cases per 100,000 person-years. Children of women who smoked during pregnancy had an increased incidence of brain tumors (hazard ratio = 1.24; 95% confidence interval: 1.01-1.53). The increase in risk was similar for benign and malignant tumors, and was most apparent for astrocytoma. The effect of smoking on the occurrence of brain tumors was seen most strongly among 2-4 year-old children.

CONCLUSIONS

These results support a role for maternal smoking during pregnancy in the etiology of childhood brain tumors. Our findings should be confirmed in other prospective studies.

Smoking and orofacial clefts: a United Kingdom-based case-control study

OBJECTIVE

To investigate the association between smoking and orofacial clefts in the United Kingdom.

DESIGN

Case-control study in which the mother's exposure to tobacco smoke was assessed by a structured interview.

SETTING

Scotland and the Manchester and Merseyside regions of England.

PARTICIPANTS

One hundred ninety children born with oral cleft between September 1, 1997, and January 31, 2000, and 248 population controls, matched with the cases on sex, date of birth, and region.

MAIN OUTCOME MEASURE

Cleft lip with or without cleft palate and cleft palate.

RESULTS

There was a positive association between maternal smoking during the first trimester of pregnancy and both cleft lip with or without cleft palate (odds ratio 1.9, 95% confidence interval 1.1 to 3.1) and cleft palate (odds ratio 2.3, 95% confidence interval 1.3 to 4.1). There was evidence of a dose-response relationship for both types of cleft. An effect of passive smoking could not be excluded in mothers who did not smoke themselves.

CONCLUSION

The small increased risk for cleft lip with or without cleft palate in the offspring of women who smoke during pregnancy observed in this study is in line with previous evidence. In contrast to some previous studies, an increased risk was also apparent for cleft palate. In these U.K. data, there was evidence of a dose-response effect of maternal smoking for both types of cleft. The data were compatible with a modest effect of maternal passive smoking, but the study lacked statistical power to detect or exclude such an effect with confidence. It may be useful to incorporate information on the effects of maternal smoking on oral clefts into public health campaigns on the consequences of maternal smoking.

Parental exposure to polycyclic aromatic hydrocarbons and the risk of childhood brain tumors: The SEARCH International Childhood Brain Tumor Study

Experimental evidence suggests that parental exposure to polycyclic aromatic hydrocarbons (PAH), which occurs primarily through tobacco smoke, occupational exposure, and air pollution, could increase the risk of cancer during childhood. Population-based case-control studies carried out in seven countries as part of the SEARCH Program compared data for 1,218 cases of childhood brain tumors and 2,223 controls (1976-1994). Parental occupational exposure to PAH during the 5-year period before birth was estimated with a job exposure matrix. Risk estimates were adjusted for child's age, sex, and study center. Paternal preconceptional occupational exposure to PAH was associated with increased risks of all childhood brain tumors (odds ratio (OR) = 1.3, 95% confidence interval: 1.1, 1.6) and astroglial tumors (OR = 1.4, 95% confidence interval: 1.1, 1.7). However, there was no trend of increasing risk with predicted level of exposure. Paternal smoking alone (OR = 1.4) was also associated with the risk of astroglial tumors in comparison with nonsmoking, non-occupationally-exposed fathers. Risks for paternal occupational exposure were higher, with (OR = 1.6) or without (OR = 1.7) smoking. Maternal occupational exposure to PAH before conception or during pregnancy was rare, and this exposure was not associated with any type of childhood brain tumor. This large study supports the hypothesis that paternal preconceptional exposure to PAH increases the risk of brain tumors in humans.

Relation of childhood brain tumors to exposure of parents and children to tobacco smoke: the SEARCH international case-control study. Surveillance of Environmental Aspects Related to Cancer in Humans

The etiology of childhood brain tumors (CBTs) remains unknown. Tobacco smoke contains several known carcinogens and can induce DNA adducts in human placenta and hemoglobin adducts in fetuses. We present the results of an international case-control study to evaluate the association between CBTs and exposure of parents and children to cigarette smoke. The study was undertaken as part of the SEARCH program of the IARC. Nine centers in 7 countries were involved. The studies mainly covered the 1980s and early 1990s. Cases (1,218, ages 0-19 years) were children newly diagnosed with a primary brain tumor; there were 2,223 population-based controls. Most mothers who agreed to participate were interviewed in person at home. Odds ratios (ORs) were calculated by unconditional logistic regression, adjusted for age, sex and center, for all types of CBT combined, 4 CBT histotypes, 5 age groups and each center. There was no association between the risk of brain tumors in the child and parental smoking prior to pregnancy, maternal smoking or regular exposure to others' cigarette smoke during pregnancy at home or at work, or passive smoking by the child during the first year of life. These results did not change considering the child's age at diagnosis, the histologic type of tumor or center.

Maternal smoking during pregnancy and the risk of childhood brain tumors: a meta-analysis of 6566 subjects from twelve epidemiological studies

OBJECTIVE

Prior epidemiological studies suggest a possible association between maternal smoking during pregnancy and risk of childhood brain tumors. A meta-analysis was performed statistically pooling all available observational studies on this topic in order to evaluate this suspected association.

METHODS

Using previously described methods, a protocol was developed for a meta-analysis examining the association between maternal smoking during pregnancy and subsequent development of primary brain tumors in their offspring. Literature search techniques, study inclusion criteria and statistical procedures were prospectively defined. Data from epidemiological studies were pooled using a general variance-based meta-analytic method employing confidence intervals previously described by Greenland. The outcome of interest was a summary relative risk (RRs) reflecting the risk of childhood brain tumor development associated with mother's smoking during the index pregnancy. Sensitivity analyses were performed when necessary to explain any observed statistical heterogeneity and/or to evaluate the impact of demographic or study characteristics on the summary estimate of effect.

RESULTS

Twelve observational studies meeting protocol specified inclusion criteria were obtained via a comprehensive literature search. These studies enrolled a total of 6566 patients. Analysis for homogeneity demonstrated that the data were homogeneous (P > 0.50) and could be statistically combined. Pooling all twelve reports yielded an RRs of 1.05 (0.90-1.21), a non-statistically significant result suggesting no clear association between maternal smoking during pregnancy and risk of childhood brain tumor development. Numerous sensitivity analyses examining the possible effect of study design and various patient characteristics failed to show any influence on the RRs further supporting the observed lack of association.

CONCLUSION

The available epidemiological data do not support a clear association between maternal smoking during pregnancy and pediatric brain tumor development. Although it appears likely that no association exists, limitations in study designs limit definitive conclusions based on available data.

Smoking status, reading level, and knowledge of tobacco effects among low-income pregnant women

BACKGROUND

Smoking during pregnancy increases the health risks of the unborn child as well as the mother. Although smoking rates for the population as a whole have declined drastically in the past generation, since 1992 there has been an increase in smoking among women, teenagers, and adults living in poverty. The purpose of this study was to assess reading level, tobacco knowledge, attitudes, and practices of tobacco use among pregnant adult and adolescent women in the public health system in north Louisiana.

METHODS

A convenience sample of 600 pregnant women was interviewed in person in the Obstetrics Clinics at Louisiana State University Health Sciences Center at Shreveport and E.A. Conway in Monroe. The structured interview contained detailed questions about smoking practices, tobacco knowledge, and attitudes. Reading was assessed using the Rapid Estimate of Adult Literacy in Medicine. Smoking practices were assessed by self-report and verified by measuring urine cotinine levels. The Cochran-Mantel-Haenszel test was used to estimate the relationship between reading level and knowledge and attitude; multiple logistic regression was used to determine which variable(s) predicted current smoking practices.

RESULTS

Knowledge about the effects of smoking and concern about the health effect of smoking on their baby varied significantly by reading level, with participants with higher reading levels having more knowledge and greater concern. Smoking practices did not vary by reading level even when race, age, and living with a smoker were controlled. Race was a significant determinant of smoking practices, with more white women reporting currently smoking during pregnancy than African Americans (34% vs 8%).

CONCLUSIONS

Reading level was related to knowledge about health effects of smoking. Women with higher reading levels were also more concerned about the adverse health effects of smoking on themselves and their babies. However, reading level was not correlated with smoking prevalence. The most significant determinant of smoking was race (with whites smoking significantly more than African Americans).

Risk factors for pediatric tumors of the central nervous system: results from a German population-based case-control study

BACKGROUND

From 1993 to 1997 we conducted two population-based case-control studies on childhood cancer and a variety of potential risk factors in Germany. One case group involved children under the age of 15 years having a tumor of the central nervous system (CNS).

PROCEDURE

For both studies, one conducted in the northwestern area of Germany, the other covering the whole of West Germany, incident cases were identified from the nationwide German Childhood Cancer Registry, and controls were randomly selected from complete population registration files.

RESULTS

In total 466 pediatric CNS tumor cases and 2,458 controls were available for analyses. We observed only few positive associations, namely, between CNS tumors and low birth weight [<2,500 g; odds ratio (OR), 1.73; 95% confidence interval (CI), 1.06-2.84], between ependymoma and maternal smoking during pregnancy (>10 cigarettes per day: OR, 4.71; 95% CI, 1.69-13.1), and between astrocytoma and exposure to wood preservatives (OR, 1.91; 95% CI, 1.22-3.01). CNS tumors were not associated with high birth weight, duration of breast feeding, maternal age at time of delivery, duration of gestation, previous fetal losses, paternal smoking during pregnancy, maternal alcohol consumption, the child's exposure to pesticides, maternal diagnostic X-ray examinations during pregnancy, X-ray examinations of the child, or exposure to residential magnetic fields.

CONCLUSIONS

Despite the large study population, we found only few factors that were associated with CNS tumors or one of the morphological subgroups. Therefore, our results suggest that aspects of the prenatal and neonatal period play only a minor role in the etiology of pediatric CNS tumors.

The miseries of passive smoking

Passive smoking is defined as an involuntary exposure to a combined but diluted cigarette sidestream smoke (SS, gas and particle phases that are evolved from the smoldering end of a cigarette while the smoker is not puffing) and the exhaled smoke from smokers. SS contains numerous cytotoxic substances such as polycyclic aromatic hydrocarbons (PAHs), aromatic amines, nitrosamines, heavy metals, poisonous gases, pesticide residues, and radioactive elements in quantities much higher than those found from the cigarette mainstream smoke (MS) which is puffed by smokers. Passive smoking is found to be the cause of death from cancers and cardiac disease. Furthermore, it damagingly involves reproductive organs, the nervous system, genetic materials, and is particularly hazardous to mother and child during pregnancy and to those with a history of asthma, chronic infections, induced or earned immune deficiency, or predisposed susceptibility.

Active and passive smoking during pregnancy and risk of central nervous system tumours in children

The effects of maternal active and passive smoking during pregnancy on childhood central nervous system (CNS) tumours were assessed in a population-based case-control study. The mothers of 244 children aged 0-15 years with CNS tumours and 502 control mothers were interviewed about their smoking habits. All families were resident in the region of Lombardy, Italy. Risk estimates were calculated by unconditional logistic regression, adjusted for age, sex and area of residence. Active smoking by the parents before pregnancy was not associated with increased risk of CNS tumours in the children. Active smoking by the mother during early pregnancy (approximately the first 5 weeks) was associated with a slightly increased risk of the child developing a CNS tumour (odds ratio [OR] 1.5 [95% CI 1.0, 2.3]). An increased risk of CNS tumours was found in the children of non-smoking mothers exposed regularly to tobacco smoke both in early pregnancy (OR 1.8 [95% CI 1.2, 2.6]) and in late pregnancy (OR 1.7 [95% CI 1.2, 2.5]). Although this study was retrospective, the results confirm our previous findings and suggest an association between the risk of developing CNS tumours in children and regular passive smoking by the mother during pregnancy.

From in utero and childhood exposure to parental smoking to childhood cancer: a possible link and the need for action

The objective of the present work is to critically summarize published studies and reassess the state of knowledge on a highly controversial topic: the potential association between prenatal exposure to passive smoking as well as maternal active smoking and postnatal exposure to environmental tobacco smoke (ETS) and enhanced incidence of childhood cancer. Elements to be considered include the substantial proportion of pregnant women who remain smokers, the widespread nature of exposure to ETS during pregnancy as well as during childhood, the known toxicology of tobacco smoke, and in particular sidestream smoke, characterized by a rich carcinogen content, the specific metabolism of foetuses and new-borns and finally the amount of epidemiologic data already available. We conducted a thorough review of the literature to identify studies either exclusively dealing with the effects of passive smoking on the occurrence of childhood cancers or more generally etiologic studies of cancer, be it overall or site-specific. We identified close to 50 publications presenting pertinent results from epidemiological investigations and about 50 more on mechanisms and metabolism, smoking in pregnancy and exposure to ETS as well as selected reviews and commentaries. Collaborative epidemiological studies were conducted in the United Kingdom (UK), USA, Sweden, Netherlands and internationally (France, Italy). In addition, other studies were also available from the USA, UK, Canada, Australia, Sweden, Italy, Denmark and People's Republic of China. The vast majority were case-control studies dealing with all cancers, leukaemia and lymphomas, central nervous system (CNS) tumours, Wilms' tumour, retinoblastoma, neuroblastoma, hepatoblastoma, rhabdomyosarcoma, bone and soft tissues tumours, germ cell tumours, as well as specific histological types of leukaemias, lymphomas or CNS tumours. No strong association between maternal smoking in pregnancy and/or exposure to ETS and childhood cancer is found. Yet, several studies found slightly increased relative risks, generally smaller than 1.5, i.e. the order of magnitude associated with some recognized hazards of exposure to ETS (1.2 to 1.3 for adult lung cancer and cardiovascular diseases). Tumours most often found associated with maternal smoking in pregnancy or ETS exposure are childhood brain tumours and leukaemia-lymphoma, with risks up to two or greater in selected studies. In a few studies, risks associated with paternal smoking are higher than the maternal ones. This evidence from human studies coupled with demonstration of genotoxic effects on the foetus of exposure to metabolites of tobacco smoke, and demonstrable presence of adducts should lead to strong recommendations aiming at fully protecting foetuses, new-borns and infants from tobacco smoke.

Smoking and male reproduction: a review

Because of the large number of men worldwide who smoke and the fact that cigarette smoke contains known mutagens and carcinogens, there has been concern that smoking may have adverse effects on male reproduction. A review of the epidemiological literature indicates that cigarette smoking is associated with modest reductions in semen quality including sperm concentration, motility and morphology. The associations between male smoking and sperm concentration and motility are stronger among studies of 'healthy' men (e.g. volunteers and sperm donors) than among men from infertility clinic populations. Smoking has also been associated with alterations in hormone levels in males, for example increases in the levels of oestrone and oestradiol. Despite modest reductions in semen quality and altered hormone levels among smokers compared to non-smokers, studies have not shown a reduction in male fertility in association with paternal smoking. There is some evidence to suggest that paternal smoking is associated with congenital anomalies and childhood cancer (with ORs in positive studies generally < 2.0). Smoking has not been shown to be mutagenic to human spermatozoa, although studies have been small and have had methodological shortcomings. It is concluded that, although smokers as a group may not experience reduced fertility, men with marginal semen quality who wish to have children may benefit from quitting smoking, since several small studies indicate the potential for improved semen quality after quitting smoking. More research on the benefits of quitting smoking among men with marginal semen quality is needed. Methodological improvements in studies aimed at clarifying the association between paternal smoking and reproductive and developmental outcomes in offspring should include obtaining accurate paternal smoking dose information, evaluating smoking exposure information in relation to various time windows (e.g. prior to conception, during gestation), and controlling for potential confounders and modifying factors such as age and maternal smoking habits. More sensitive and specific laboratory assays and increased sample sizes are required to establish whether smoking induces mutations in human spermatozoa.

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.