Passive smoking in never-smokers is associated with increased plasma homocysteine levels

Indoor air pollution from coal combustion and tobacco smoke during the periconceptional period and risk for neural tube defects in offspring in five rural counties of Shanxi Province, China, 2010-2016

Indoor air pollution may increase the risk for neural tube defects (NTDs) in Chinese rural populations. However, this association remains a subject of debate. We conducted a population-based case-control study of 222 NTD and 517 control mothers recruited between 2010 and 2016 in five rural areas in northern China. An indoor air pollution exposure evaluation index (IAPEEI) was used to evaluate mothers' exposure to tobacco-sourced and coal-sourced indoor air pollution. Essential characteristics were collected using structured questionnaires within 10 days of delivery. We found that exposure to indoor air pollution (IAPEEI ≥ 1) can lead to 3.41 times the risk of conceiving NTD fetuses compared with the no-exposure group (IAPEEI = 0) (adjusted odds ratio and 95 % confidence interval: 3.41 [2.34-5.02]). The risk increased with increasing IAPEEI score, indicating a clear dose-response trend (P < 0.001). Using a coal stove for heating (especially in the bedroom) and passive smoking are significantly associated with an increased likelihood of NTD occurrence. Exposure to indoor air pollution is a daily reality for rural women in China, and its impact on reproductive health deserves extensive attention.

Clinical Risk Factors Associated with Ambulatory Outcome in Acute Ischemic Stroke Patients Smokers Treated with Thrombolytic Therapy

BACKGROUND

Patients who have suffered an acute ischemic stroke (AIS) and are smokers may have a better outcome following thrombolytic therapy when compared with non-smokers. While this finding is controversial, data on baseline clinical risk factors to predict treatment efficacy of thrombolytic therapy using ambulatory status in patients who suffered AIS and are smokers is not common.

METHODS

Between 2010 and 2016, retrospective data on patients who have suffered an AIS and received recombinant tissue plasminogen activator (rtPA) were obtained from Greenville health system registry. Assessment of clinical risk factors and the likelihood of an improvement in post-stroke ambulation among smokers and non-smokers was carried out using multivariate logistic regression.

RESULTS

Of 1001 patients, 70.8% were smokers and 29.2% non-smokers. Among the smokers and non-smokers, 74.6% and 84.6% improvement in ambulation respectively at discharge. The odds of improved ambulation decrease among smokers as age group increases compared to those below 50 [(60-69 years, aOR, 0.30, 95% C.I, 0.108-0.850, p < 0.05), (70-79 years aOR, 0.27, 95% C.I, 0.096-0.734, p < 0.05), (80+ years aOR, 0.16, 95% C.I, 0.057-0.430, P < 0.01). Patients with National Institute of Health Stroke Scale Score (NIHSS) score > 7 (reference <7) were 91% less likely to have improved ambulation among smokers and non-smokers (aOR, 0.09, 95% C.I, 0.055-0.155, P = 0.01), and (aOR, 0.08, 95% C.I, 0.027-0.214, P = 0.01) respectively. Atrial fibrillation was an independent predictor of decreased improvement in ambulation only among smokers (aOR, 0.58, 95% C.I, 0.356-0.928 P < 0.05).

CONCLUSION

Our findings suggest that elderly smokers with atrial fibrillation would benefit more from aggressive management of atrial fibrillation than non-smokers.

In acute ischemic stroke patients with smoking incidence, are more women than men more likely to be included or excluded from thrombolysis therapy?

Background:

Clinical factors associated with exclusion from recombinant tissue plasminogen activator in both men and women are not completely understood. The aim of this study is to determine whether there is a gender difference in clinical risk factors that excluded ischemic stroke patients with a history of smoking from recombinant tissue plasminogen activator.

Methods:

Retrospective data from a stroke registry were analyzed, and multivariable linear regression models were used to determine gender differences. Logistic regression models determined exclusion clinical risk factors for thrombolysis in male and female acute ischemic stroke patients with a history of smoking, while sequentially adjusting for sociodemographic, clinical, and stroke-related variables. The Kaplan–Meier survival analysis was used to determine the exclusion probabilities of men and women with a history of smoking within the stroke population.

Results:

Of the 1,446 acute ischemic stroke patients eligible for recombinant tissue plasminogen activator, 379 patients with a history of smoking were examined, of which 181 received recombinant tissue plasminogen activator while 198 were excluded from receiving recombinant tissue plasminogen activator. Of the 198 patients, 75 females and 123 males were excluded from receiving recombinant tissue plasminogen activator. After multivariable adjustment for age, National Institutes of Health scores, and stroke-related factors, females who present with weakness/paresis on initial examination (OR = 0.117, 95% CI, 0.025–0.548) and men who present with a history of previous transient ischemic attack (OR = 0.169, 95% CI, 0.044–0.655), antiplatelet medication use (OR = 0.456, 95% CI, 0.230–0.906), and weakness/paresis on initial examination (OR = 0.171, 95% CI, 0.056–0.521) were less likely to be excluded from recombinant tissue plasminogen activator (thrombolysis therapy).

Conclusions:

In an ischemic stroke population with a history of smoking, female smokers are more likely to be excluded from thrombolysis therapy in comparison to men, even after adjustment for confounding variables.

Biochemical and Hematological Correlates of Elevated Homocysteine in National Surveys and a Longitudinal Study of Urban Adults

Elevated blood homocysteine (Hcy) among middle-aged adults can increase age-related disease risk, possibly through other biochemical and hematological markers. We selected markers for hyperhomocysteinemia among middle-aged adults, studied time-dependent Hcy-marker associations and computed highly predictive indices of hyperhomocysteinemia, with cross-sectional and longitudinal validations. We used data from the National Health and Nutrition Examination Survey (NHANES III, phase 2, n_max = 4000), the NHANES 1999–2006 (n_max = 10,151) and pooled NHANES (cross-sectional validation). Longitudinal validation consisted of mixed-effects linear regression models (Hcy predicting markers’ annual rates of change), applied to the Healthy Aging in Neighborhoods of Diversity Across the Life Span (HANDLS, n = 227–244 participants, k = 2.4 repeats/participant, Age_base: 30–65 years) data. Machine learning detected nine independent markers for Hcy > 14 µmol/L (NHANES III, phase 2): older age; lower folate and B-12 status; higher serum levels of creatinine, uric acid, alkaline phosphatase, and cotinine; mean cell hemoglobin and red cell distribution widths (RDW); results replicated in the 1999–2006 NHANES [AUC = 0.60–0.80]. Indices combining binary markers increased elevated Hcy odds by 6.9–7.5-fold. In HANDLS, first-visit Hcy predicted annual increase in creatinine, RDW and alkaline phosphatase, with third-visit index (2013–2018) directly predicting Hcy (2004–2009). We provide evidence of the internal and external validity of indices composed of several biomarkers that are strongly associated with elevated Hcy.

Association between smoking status and homocysteine levels and possible effect modification by cholesterol and oestradiol

Introduction: This study aimed to examine the association of smoking status with homocysteine levels and to determine whether the association is modified by oestradiol or cholesterol.Methods: Data (N = 4580) were obtained from National Health and Nutrition Examination Survey 2003-2004 with analysis done in 2018 on adults aged ≥20 years. The outcome was homocysteine; smoking status was the exposure variable and categorized as current, former or never smoker. Generalized linear models were used to examine the associations between smoking status and homocysteine levels, while assessing the impact of oestradiol and cholesterol.Results: After adjusting for age, sex, ethnicity, education and income level, homocysteine levels did differ by smoking status ((current smokers versus never smokers: β: 0.18 CI: 0.00, 0.36), (former smokers: β: 0.10 CI: -0.09, 0.28)). The addition of oestradiol as an interaction term in adjusted models was associated with a 16.6% increase in homocysteine levels when compared to models without the interaction term. Oestradiol but not cholesterol did moderate the association between smoking status and homocysteine levels.Discussion and conclusions: Homocysteine levels did differ across smoking status after adjusting for confounders. Oestradiol did moderate the relationship between homocysteine and smoking status.

Meta-analysis of the association of maternal smoking and passive smoking during pregnancy with neural tube defects

BACKGROUND

It is unclear whether the incidence of neural tube defects (NTDs) is greater with maternal smoking or with passive smoking during pregnancy.

OBJECTIVES

To compare the effects of smoking and passive smoking during pregnancy on the risk of NTDs.

SEARCH STRATEGY

English and Chinese databases were searched for relevant papers published before March 2017, using search terms including "smoking" and "NTD."

SELECTION CRITERIA

Case-control and cohort studies on the aforementioned association were included.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted the original data. Meta-analyses were performed to assess the risks associated with smoking and passive smoking, followed by a comparison of the two pooled effect estimates. The I² statistic was used to examine between-study heterogeneity.

MAIN RESULTS

The final analysis included 23 articles representing 33 studies. The pooled odds ratio (OR) and 95% confidence interval (CI) for the risk of NTDs was 1.052 (0.907-1.220) with smoking and 1.898 (1.557-2.313) with passive smoking. Comparison of these ORs indicated that the risk of NTDs was higher with passive smoking than with smoking (OR 1.804, 95% CI 1.409-2.309).

CONCLUSIONS

Compared with smoking, exposure to passive smoking during pregnancy carries a higher risk of having infants with NTDs.

Clinical Manifestations of Isolated Elevated Homocysteine-Induced Peripheral Neuropathy in Adults

OBJECTIVE

To characterize the clinical features of isolated elevated plasma homocysteine (eHcy)-induced peripheral neuropathy (IHIN) in adults.

METHODS

Charts of subjects with the diagnosis of IHIN who visited neuromuscular clinic from January 01, 2012 to September 30, 2014 were reviewed. Subjects with identifiable etiologies for neuropathy, such as B12/folate deficiency; metabolic, toxic, endocrinologic, infectious/inflammatory renal or liver diseases; or traumatic nerve injury, were excluded. Their clinical presentations were recorded and analyzed.

RESULTS

Thirty subjects (age: 63.2 ± 14.8 years, 13 males) were included. They all had an isolated increased homocysteine level (15.4 ± 5.3 μmol/L) but normal levels of B12, folate, and methylmalonic acid. Of 30, 14 (46.7%) had numb feet, 11 (36.7%) had numb hands, 7 (23.3%) had pain in lower extremities, and 10 (33.3%) had tingling in feet. Distal sensory deficits were present in 18/30 (60%) patients. Distal limb weakness was seen in 4 and decreased tendon reflexes in 12 patients.

CONCLUSIONS

Sensory deficits are predominant components of IHIN. Characterizing clinical features of IHIN would help better understand eHcy-related neuropathy and improve its management.

Determinants of hyperhomocysteinemia in healthy and hypertensive subjects: A population-based study and systematic review

AIMS

Hyperhomocysteinemia (HHcy) is known to increase the risk of many diseases. Factors influencing HHcy in healthy and hypertensive subjects remain under-researched.

METHODS

A large population-based study was conducted in 60 communities from Shenzhen, China. Responses to standardized questions on lifestyle factors and blood samples were collected from all participants after a 12-h overnight fast. Multiple linear and multivariate logistic regressions were used to explore risk factors for HHcy. Results were then compared to those from a systematic review of English-language articles listed in Pubmed, EBSCOhost, Web of Science, Embase and Cochrane libraries that investigated HHcy risk factors in healthy and hypertensive subjects.

RESULTS

A total of 1586 healthy (Male/Female = 642/944) and 5935 hypertensive subjects (Male/Female = 2928/3007) participated in our population-based study. In logistic regression analyses, age, BMI and creatinine (Cr) were risk factors, while being female, fruit intake and physical activity were protective factors for HHcy in healthy subjects. In hypertensive subjects, seven [age, smoking, salt intake, systolic blood pressure (SBP), uric acid, triglycerides (TG), and Cr] and four [female, fruit intake, total cholesterol (TC), and glucose] factors were associated with higher and lower HHcy respectively. The review of 71 studies revealed that potential risk factors for Hcy included nutritional, physiologic, lifestyle habits, ethnicity, genetics, interactions between gene-environment, gene-gene, gene-nutritional, environment-environment, nutritional-nutritional.

CONCLUSION

Our study indicates the potential importance of increasing folic acid and vitamin B supplementation, daily fruit and vegetable intake, regular exercise and refraining from tobacco smoking and alcohol consumption as preventive strategies for Hcy.

Associations between maternal periconceptional exposure to secondhand tobacco smoke and major birth defects

BACKGROUND

While associations between secondhand smoke and a few birth defects (namely, oral clefts and neural tube defects) have been noted in the scientific literature, to our knowledge, there is no single or comprehensive source of population-based information on its associations with a range of birth defects among nonsmoking mothers.

OBJECTIVE

We utilized data from the National Birth Defects Prevention Study, a large population-based multisite case-control study, to examine associations between maternal reports of periconceptional exposure to secondhand smoke in the household or workplace/school and major birth defects.

STUDY DESIGN

The multisite National Birth Defects Prevention Study is the largest case-control study of birth defects to date in the United States. We selected cases from birth defect groups having >100 total cases, as well as all nonmalformed controls (10,200), from delivery years 1997 through 2009; 44 birth defects were examined. After excluding cases and controls from multiple births and whose mothers reported active smoking or pregestational diabetes, we analyzed data on periconceptional secondhand smoke exposure-encompassing the period 1 month prior to conception through the first trimester. For the birth defect craniosynostosis, we additionally examined the effect of exposure in the second and third trimesters as well due to the potential sensitivity to teratogens for this defect throughout pregnancy. Covariates included in all final models of birth defects with ≥5 exposed mothers were study site, previous live births, time between estimated date of delivery and interview date, maternal age at estimated date of delivery, race/ethnicity, education, body mass index, nativity, household income divided by number of people supported by this income, periconceptional alcohol consumption, and folic acid supplementation. For each birth defect examined, we used logistic regression analyses to estimate both crude and adjusted odds ratios and 95% confidence intervals for both isolated and total case groups for various sources of exposure (household only; workplace/school only; household and workplace/school; household or workplace/school).

RESULTS

The prevalence of secondhand smoke exposure only across all sources ranged from 12.9-27.8% for cases and 14.5-15.8% for controls. The adjusted odds ratios for any vs no secondhand smoke exposure in the household or workplace/school and isolated birth defects were significantly elevated for neural tube defects (anencephaly: adjusted odds ratio, 1.66; 95% confidence interval, 1.22-2.25; and spina bifida: adjusted odds ratio, 1.49; 95% confidence interval, 1.20-1.86); orofacial clefts (cleft lip without cleft palate: adjusted odds ratio, 1.41; 95% confidence interval, 1.10-1.81; cleft lip with or without cleft palate: adjusted odds ratio, 1.24; 95% confidence interval, 1.05-1.46; cleft palate alone: adjusted odds ratio, 1.31; 95% confidence interval, 1.06-1.63); bilateral renal agenesis (adjusted odds ratio, 1.99; 95% confidence interval, 1.05-3.75); amniotic band syndrome-limb body wall complex (adjusted odds ratio, 1.66; 95% confidence interval, 1.10-2.51); and atrial septal defects, secundum (adjusted odds ratio, 1.37; 95% confidence interval, 1.09-1.72). There were no significant inverse associations observed.

CONCLUSION

Additional studies replicating the findings are needed to better understand the moderate positive associations observed between periconceptional secondhand smoke and several birth defects in this analysis. Increased odds ratios resulting from chance (eg, multiple comparisons) or recall bias cannot be ruled out.

Hyperhomocysteinemia Is Associated with Vitamin B-12 Deficiency: A Cross-sectional Study in a Rural, Elderly Population of Shanxi China

OBJECTIVES

To report the association of lifestyle factors and plasma vitamin B-12 with hyperhomocysteinemia in a large sample of men and women living in a region of China where there is an increased risk of NTDs.

DESIGN

Community-based, cross-sectional study of Lvliang City, Shanxi Province, China.

SETTING

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease (CVD) and a sensitive marker of vitamin B-12 and folate deficiency.

PARTICIPANTS

A total of 2355 (1044 men and 1311 women) participants born before 1 January 1958 (≥55 years of age) and living in Lvliang City for at least 2 months a year were included.

MEASUREMENTS

The participants were assessed regarding demographic characteristics, height, weight, as well as having a physical examination and blood sampling for serum cholesterol, total homocysteine (tHcy), folate, and vitamin B12 levels.

RESULTS

The median (25th-75th percentile) tHcy concentration was 21.5 (15.8-33.6) µmol/L in men and 18.0 (13.4-24.8) µmol/L in women. The overall prevalence of hyperhomocysteinemia (tHcy ≥15 µmol/L) was 72.6% (84.3% in men and 63.2% in women), inversely correlated with folate (r=-0.230, P=0.006) and vitamin B-12 (r=-0.540, P<0.001), and positively correlated with uric acid (r=0.054, P<0.001). Vitamin B-12 and folate deficiency, older age, and male gender were associated with elevated tHcy; with vitamin B-12 deficiency being the strongest.

CONCLUSIONS

Plasma tHcy concentration and hyperhomocysteinemia were significantly higher in this population than in previously studied populations. Vitamin B-12 and folate supplementation, concomitant lifestyle changes such as smoking cessation, and lipid-lowering treatments may help to decrease plasma tHcy concentrations and reduce the CVD risk in this population.

The shared pathoetiological effects of particulate air pollution and the social environment on fetal-placental development

Exposure to particulate air pollution and socioeconomic risk factors are shown to be independently associated with adverse pregnancy outcomes; however, their confounding relationship is an epidemiological challenge that requires understanding of their shared etiologic pathways affecting fetal-placental development. The purpose of this paper is to explore the etiological mechanisms associated with exposure to particulate air pollution in contributing to adverse pregnancy outcomes and how these mechanisms intersect with those related to socioeconomic status. Here we review the role of oxidative stress, inflammation and endocrine modification in the pathoetiology of deficient deep placentation and detail how the physical and social environments can act alone and collectively to mediate the established pathology linked to a spectrum of adverse pregnancy outcomes. We review the experimental and epidemiological literature showing that diet/nutrition, smoking, and psychosocial stress share similar pathways with that of particulate air pollution exposure to potentially exasperate the negative effects of either insult alone. Therefore, socially patterned risk factors often treated as nuisance parameters should be explored as potential effect modifiers that may operate at multiple levels of social geography. The degree to which deleterious exposures can be ameliorated or exacerbated via community-level social and environmental characteristics needs further exploration.

Maternal periconceptional exposure to cigarette smoking and congenital limb deficiencies

BACKGROUND

Congenital limb deficiencies (LD)s are characterised by the failure or disruption in formation of limbs or digits. Epidemiological research on maternal exposure to cigarette smoke and LDs is inconclusive.

METHODS

Data from the National Birth Defects Prevention Study were used to examine LDs and maternal exposure to active or passive cigarette smoke. Mothers of LD case (n = 906) and unaffected control (n = 8352) pregnancies from October 1997 through December 2007 reported on exposure type and quantity. Logistic regression was used to estimate adjusted odds ratio (OR) and 95% confidence interval [95% CI]; interactions with folic acid (FA) intake were tested.

RESULTS

For any LD, ORs were elevated for active (1.24 [95% CI 1.01, 1.53]), passive (home) (1.28 [95% CI 1.03, 1.59]), and 'active and passive' (1.34 [95% CI 1.05, 1.70]) exposures. The ORs for longitudinal LDs were elevated for passive (home) (1.62 [95% CI 1.14, 2.31]) and 'active and passive' (1.62 [95% CI 1.09, 2.41]) exposures. The OR for pre-axial LDs were elevated for any (1.39 [95% CI 1.01, 1.90]), active (1.53 [95% CI 1.03, 2.29]), passive (home) (1.82 [95% CI 1.23, 2.69]), and 'active and passive' (1.87 [95% CI 1.20, 2.92]) exposures. For lower limbs, ORs were elevated for passive (home) (1.44 [95% CI 1.01, 2.04]) and smoking 15 or more cigarettes/day (2.25 [95% CI 1.27, 3.97]). Interactions showed that ORs for any passive smoke exposure were 0.43 and 0.59 higher in the absence of FA intake for any and terminal transverse LDs.

CONCLUSIONS

Maternal active smoking and exposure to passive cigarette smoke emerged as a potential teratogen that affects limb and digit formation. FA was not found to mitigate the impact.

Maternal passive smoking during pregnancy and neural tube defects in offspring: a meta-analysis

PURPOSE

This study aims to examine the association between maternal passive smoking during pregnancy and the occurrence of neural tube defects (NTDs) in offspring.

METHODS

We retrieved studies published on the association between maternal passive smoking during pregnancy and the occurrence of NTDs in offspring. Meta-analysis was applied to calculate the pooled effect estimates and their 95% confidence intervals (CIs) using data from 10 case-control studies. The publication bias was assessed by the Egger's regression asymmetry test and Begg's rank correlation test with Begg's funnel plot.

RESULTS

The pooled effect estimate of maternal passive smoking was 1.82 (95% CI 1.46-2.27) for total NTDs; the effect estimates were 1.72 (95% CI 1.44-2.06), 1.52 (95% CI 1.29-1.79), and 2.32 (95% CI 1.34-4.01) for NTDs subtypes of anencephaly, spina bifida and encephalocele, respectively. Stratified by geographic region of the studies, the pooled effect estimates were 2.11 (95% CI 1.46-3.06), 1.65 (95% CI 1.16-2.34), 1.25 (95% CI 0.41-3.80) in China, USA and Iran, respectively.

CONCLUSIONS

This meta-analysis suggested that maternal passive smoking during pregnancy was associated with an increased risk of total NTDs and three NTDs subtypes in offspring. Specifically, the associations were also found to be significantly positive both in China and USA.

Dietary supplement use and smoking are important correlates of biomarkers of water-soluble vitamin status after adjusting for sociodemographic and lifestyle variables in a representative sample of U.S. adults

Biochemical indicators of water-soluble vitamin (WSV) status were measured in a nationally representative sample of the U.S. population in NHANES 2003-2006. To examine whether demographic differentials in nutritional status were related to and confounded by certain variables, we assessed the association of sociodemographic (age, sex, race-ethnicity, education, income) and lifestyle (dietary supplement use, smoking, alcohol consumption, BMI, physical activity) variables with biomarkers of WSV status in adults (aged ≥ 20 y): serum and RBC folate, serum pyridoxal-5'-phosphate (PLP), serum 4-pyridoxic acid, serum total cobalamin (vitamin B-12), plasma total homocysteine (tHcy), plasma methylmalonic acid (MMA), and serum ascorbic acid. Age (except for PLP) and smoking (except for MMA) were generally the strongest significant correlates of these biomarkers (|r| ≤ 0.43) and together with supplement use explained more of the variability compared with the other covariates in bivariate analysis. In multiple regression models, sociodemographic and lifestyle variables together explained from 7 (vitamin B-12) to 29% (tHcy) of the biomarker variability. We observed significant associations for most biomarkers (≥ 6 of 8) with age, sex, race-ethnicity, supplement use, smoking, and BMI and for some biomarkers with PIR (5 of 8), education (1 of 8), alcohol consumption (4 of 8), and physical activity (5 of 8). We noted large estimated percentage changes in biomarker concentrations between race-ethnic groups (from -24 to 20%), between supplement users and nonusers (from -12 to 104%), and between smokers and nonsmokers (from -28 to 8%). In summary, age, sex, and race-ethnic differentials in biomarker concentrations remained significant after adjusting for sociodemographic and lifestyle variables. Supplement use and smoking were important correlates of biomarkers of WSV status.

Folate and vitamin B-12 biomarkers in NHANES: history of their measurement and use

NHANES measured folate and vitamin B-12 status biomarkers, starting with serum folate from NHANES I (1974-1975) through 2010. Subsequent NHANES measured additional biomarkers [eg, red blood cell folate, serum vitamin B-12, total homocysteine (tHcy), methylmalonic acid, serum folic acid, and 5-methyltetrahydrofolic acid]. Examples of the uses of these data are wide ranging and include public policy applications, the derivation of reference intervals, and research. Periodically, the National Center for Health Statistics and its federal partners convene expert panels to review the use of the folate- and vitamin B-12-related biomarkers in NHANES. These panels have evaluated the need for results to be comparable across time and with published data and the use of crossover studies and adjustment equations to ensure comparability. With the recent availability of reference methods and materials for serum folate and tHcy, NHANES has started to use traceability approaches to enhance the accuracy and comparability of its results. A major user concern over the years has been the use of cutoffs to estimate the prevalence of inadequate folate and vitamin B-12 status. Because these cutoffs depend on the measurement procedure, several expert panels suggested approaches for dealing with cutoff challenges. This review summarizes the history and use of folate- and vitamin B-12-related biomarkers beginning with NHANES I (1974-1975) through 2010.

Maternal smoking, passive tobacco smoke, and neural tube defects

BACKGROUND

Although cigarette smoke is a well-established toxin and harmful to the developing embryo, the evidence for an independent effect on the occurrence of neural tube defects (NTDs) is mixed. In this study, we examined the relation between NTDs and maternal exposures to cigarette smoke, including passive smoke exposure.

METHODS

We used cases and controls from the large, multistate, population-based National Birth Defects Prevention Study. A total of 1041 NTD cases and 5862 live birth controls, delivered during 1997 to 2004, were available for analyses. Mothers were interviewed by telephone between 6 weeks and 24 months after delivery. Participation rates were 71% for NTD case mothers and 69% for control mothers.

RESULTS

Compared with nonsmokers (and also not exposed to passive cigarette smoke), mothers exposed only to passive smoke had an increased NTD odds ratio (OR, 1.7; 95% confidence interval [CI], 1.4-2.0), adjusted for race-ethnicity, and study center. There was no increased OR for mothers who actively smoked 24 or fewer cigarettes per day. Mothers who smoked 25 or more cigarettes per day had an elevated OR (OR, 1.6; 95% CI, 0.9-3.0), but the OR adjusted for race-ethnicity, and center was compatible with the null.

CONCLUSION

Results suggest that maternal exposure to passive smoke is associated with NTDs. Women who plan on becoming pregnant should minimize their exposure to passive smoke and refrain from smoking.