Metal exposure and bone remodeling during pregnancy: Results from the PROGRESS cohort study.

Pregnancy is characterized by high bone remodeling and might be a window of susceptibility to the toxic effects of metals on bone tissue. The aim of this study was to assess associations between metals in blood [lead (Pb), cadmium (Cd)and arsenic (As)] and bone remodeling during pregnancy. We studied pregnant woman from the PROGRESS Cohort (Programming Research in Obesity, Growth, and Environment and Social Stress). We measured concentrations of metals in blood and obtained measures of bone remodeling by quantitative ultrasound (QUS) at the radius in the second and third trimester of pregnancy. To account for chronic lead exposure, we measured lead in tibia and patella one-month postpartum with K-shell X-ray fluorescence. We assessed cross-sectional and longitudinal associations between multiple-metal concentrations and QUS z-scores using linear regression models and linear mixed models adjusted for potential confounders. Third trimester blood Cd concentrations were marginal associated with lower QUS z-scores [-0.16 (95% CI: -0.33, 0.007); P-Value = 0.06]. Mixed models showed that blood Cd was longitudinally and marginally associated with an average of -0.10 z-score (95% CI: -0.21, 0.002; P-Value = 0.06) over the course of pregnancy. Associations for Pb and As were all inverse however none reached significance. Additionally, bone Pb concentrations in patella, an index of cumulative exposure, were significantly associated with -0.06 z-score at radius (95% CI: -0.10, -0.01; P-Value = 0.03) during pregnancy. Pb and Cd blood levels are associated with lower QUS distal radius z-scores in pregnant women. Bone Pb concentrations in patella were negatively associated with z-score at radius showing the long-term effects of Pb on bone tissue. However, we cannot exclude the possibility of reverse causality for patella Pb and radius z-score associations. Our results support the importance of reducing women's metal exposure during pregnancy, as metals exposure during pregnancy may have consequences for bone strength later in life. The main finding of our study is the association between Cd blood levels and radius z-score during pregnancy. Bone lead in patella was also negatively associated with radius z-scores.

Association of Dietary Fluoride Intake and Diet Variables with Dental Caries in Adolescents from the ELEMENT Cohort Study.

To examine the association of dietary fluoride intake, total carbohydrate consumption and other key dietary variables with dental caries experience among adolescents, a cross-sectional analysis was conducted in a sample of 402 participants from the Early Life Exposures in Mexico to Environmental Toxicants cohort. The presence and severity of dental caries were assessed using the International Caries Detection and Assessment System (ICDAS) to calculate the number of decayed, missing, and filled teeth or surfaces (D1MFT/D4MFT). The dietary intake of fluoride, energy, carbohydrates, and food groups was estimated using a validated food frequency questionnaire (FFQ). Multivariate zero-inflated negative binomial regression models and negative binomial regression models were run to estimate the association of fluoride intake (mg/day) and total carbohydrate intake (g/day) with the D1MFT/D4MFT index. We found that 80% of the adolescents experienced dental caries (D1MFT >0), with 30% presenting cavitated lesions (D4MFT >0). The mean scores for D1MFT and D4MFT were 6.2 (SD 5.3) and 0.67 (SD 1.3), respectively. The median intake of fluoride estimated by the FFQ was 0.015 mg/kg/day. This intake was statistically higher in participants with a D4MFT = 0 compared to those with a D4MFT >0 (0.90 vs. 0.82 mg/day; 0.016 vs. 0.014 mg/kg/day; p < 0.05). For D1MFT, D1MFS, D4MFT, and D4MFS scores, a higher fluoride consumption (mg/day) from foods and beverages was associated with a statistically significant reduction in the number of lesions. The reported frequency of consumption of sugary foods in a whole day was statistically higher in those with D1MFT >0 than in those with D1MFT = 0 (p < 0.05). The total carbohydrate intake (g/day) was positively associated with dental caries experience. We conclude that a higher fluoride intake through foods and beverages is associated with a lower dental caries experience among adolescents; this effect was seen even when the dietary intake of fluoride was 0.015 mg/kg/day, which is lower than the average intake recommendation. In contrast, a higher total carbohydrate intake and the frequency of intake of sugary foods were associated with a higher dental caries experience, with no apparent threshold for the effects.

Trimester-Specific Associations of Prenatal Lead Exposure With Infant Cord Blood DNA Methylation at Birth.

Gestational exposure to lead (Pb) adversely impacts offspring health through multiple mechanisms, one of which is the alteration of the epigenome including DNA methylation. This study aims to identify differentially methylated CpG sites associated with trimester-specific maternal Pb exposure in umbilical cord blood (UCB) leukocytes. Eighty-nine mother-child dyads from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) longitudinal birth cohorts with available UCB samples were selected for DNA methylation analysis via the Infinium Methylation EPIC BeadChip, which quantifies methylation at >850 000 CpG sites. Maternal blood lead levels (BLLs) during each trimester (T1: 6.56 ± 5.35 µg/dL; T2: 5.93 ± 5.00 µg/dL; T3: 6.09 ± 4.51 µg/dL), bone Pb (patella: 11.8 ± 9.25 µg/g; tibia: 11.8 ± 6.73 µg/g), a measure of cumulative Pb exposure, and UCB Pb (4.86 ± 3.74 µg/dL) were measured. After quality control screening, data from 786 024 CpG sites were used to identify differentially methylated positions (DMPs) and differentially methylated regions (DMRs) by Pb biomarkers using separate linear regression models, controlling for sex and estimated UCB cell-type proportions. We identified 3 DMPs associated with maternal T1 BLL, 2 with T3 BLL, and 2 with tibia bone Pb. We identified one DMR within PDGFRL associated with T1 BLL, one located at chr6:30095136-30095295 with T3 BLL, and one within TRHR with tibia bone Pb (adjusted P-value < .05). Pathway analysis identified 15 overrepresented gene pathways for differential methylation that overlapped among all 3 trimesters with the largest overlap between T1 and T2 (adjusted P-value < .05). Pathways of interest include nodal signaling pathway and neurological system processes. These data provide evidence for differential methylation by prenatal Pb exposure that may be trimester-specific.

Bedtimes and Blood Pressure: A Prospective Cohort Study of Mexican Adolescents.

INTRODUCTION: Hypertension affects up to 5% of children worldwide and predicts later cardiovascular morbidity. Associations of short sleep and hypertension have been frequently reported in adults but less consistently in children. This study aims to examine the role of late bedtimes, a marker of short sleep duration, and potentially misaligned circadian rhythms, on incident elevated blood pressure (BP) in a large cohort of Mexican children. METHODS: Participants included 2,033 adolescents recruited from public schools in Morelos, Mexico, free from elevated BP (<90th sex, age, and height-standardized percentile). Fourteen months later, all adolescents had a second BP assessment. We abstracted baseline habitual bedtimes from questionnaires to evaluate the association between bedtime and elevated BP incidence (≥90th percentile). Risk ratios and 95% confidence intervals were estimated with discrete-time mixed survival models, adjusting for potential confounders and accounting for clustering by school. RESULTS: Participants were 12.5 (SD = 0.6) years old at baseline. At the follow-up visit 10% of adolescents had developed elevated BP. Compared to participants with a habitual weekday bedtime between 9 and 10 pm, those with a weekday bedtime 11 pm or later had a 1.87 times higher risk of developing elevated BP over the follow-up period (95% CI = 1.09, 2.21), after accounting for confounders. Participants with earlier weekday bedtimes also had a higher risk of elevated BP (RR = 1.96; 95% CI = 1.27, 3.01). The associations persisted after accounting for wake time. CONCLUSION: These data showed a U-shaped association between weekday bedtime and elevated/high BP risk among Mexican adolescents.

Association between fluoride exposure and cardiometabolic risk in peripubertal Mexican children.

BACKGROUND: Several animal studies have suggested that fluoride exposure may increase the levels of cardiometabolic risk factors, but little is known about whether fluoride exposure is associated with such risk in humans. OBJECTIVES: We examined the cross-sectional association between peripubertal exposure to fluoride and markers of cardiometabolic risk in 280 girls and 256 boys at age 10-18 years living in Mexico City. METHODS: We measured plasma fluoride concentration using a microdiffusion method. We collected data on anthropometry including BMI, waist circumference (WC) and trunk fat percentage. We measured serum markers of cardiometabolic risk, including fasting glucose, insulin and lipids. All the indicators of outcome were converted to age- and sex-specific z-scores. We also calculated a summary cardiometabolic risk score for each participant. Multivariable linear regression models were used to examine these associations. RESULTS: The geometric mean (95% confidence interval (CI)) of plasma fluoride was 0.21 µmol/L (0.20, 0.23 µmol/L) in the total sample. In girls, plasma fluoride concentrations were associated with higher z-scores for all the individual markers (except for lipids) and for the combined cardiometabolic risk score (risk score: ß = 1.28, 95% CI: 0.57-2.00, p-sex interaction = 0.02)), adjusting for covariates. No associations were found in boys. CONCLUSIONS: We found that higher peripubertal fluoride exposure at the levels observed in this study population was significantly associated with increased levels of cardiometabolic risk factors in Mexican girls but not boys. Future studies with a longitudinal design are needed to confirm our findings and further elucidate the role of fluoride in cardiometabolic risk.

Phthalate exposure during pregnancy and long-term weight gain in women.

BACKGROUND: Phthalates are known endocrine disruptors and peroxisome proliferator-activated receptor (PPAR) activators, potentially capable of promoting an obesogenic effect. Pregnant women are especially vulnerable to phthalate exposure due to physiological and metabolic changes during pregnancy, including those related to the metabolism of xenobiotics. Phthalate exposure during pregnancy has been associated with early gestational weight gain, however, its effect on long-term weight gain remains unclear. The aim of the present study was to evaluate the association between phthalate exposure during pregnancy and long-term changes in weight among women. METHODS: Urinary phthalate concentrations, socioeconomic, anthropometry and information on diet and socioeconomic status were collected during pregnancy from 178 women from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) birth cohort. Maternal body weight and diet information was also collected up to 5 times in the first year postpartum and twice during follow-up visits 5.2-10.7 years later. A path analysis was performed to assess associations between urinary phthalate metabolite levels during pregnancy and change in weight (kg) per year after delivery, including age, education, living with/without partner, parity, daily energy intake and breastfeeding duration. RESULTS: The mean age at pregnancy was 27.3 ±â€¯5.9 years and mean body mass index during the first postpartum year was 27.07 ±â€¯4.22 kg/m2. On average, women gained 3.48 kg (0.52 ±â€¯0.84 kg/year). A unit increase in log-transformed mono-3-carboxypropyl phthalate (MCPP) was associated with 0.33 kg (95% CI: 0.09, 0.56) higher weight gain per year, and mono-benzyl phthalate (MBzP) with 0.21 kg (95% CI: -0.38, -0.03) lower weight gain per year. CONCLUSION: Exposure to certain phthalates during pregnancy may be associated with long-term weight change in women. More studies on the effects of phthalate exposure during pregnancy on women's long-term health are required.

Second trimester extracellular microRNAs in maternal blood and fetal growth: An exploratory study.

Healthy feto-maternal communication is critical during pregnancy and is orchestrated by the placenta. Dysfunction of the placenta leads to fetal growth complications; however, the underlying biological mechanisms have yet to be fully elucidated. Circulating extracellular microRNAs (exmiRNAs) in the blood have been implicated in cell-to-cell communication. Therefore, exmiRNAs may provide useful biological information about communication between the mother, the fetus, and the placenta during pregnancy. We used logistic regression to determine the association of exmiRNAs with abnormal fetal growth by comparing mothers of infants classified as small-for-gestational age (SGA) (n = 36) and large-for-gestational age (LGA) (n = 13) to appropriate-for-gestational age (AGA), matched by gestational age at delivery and infant sex. In addition, we used linear regression to determine associations between exmiRNAs and birth weight-for-gestational age (BWGA) z-score (n = 100), adjusting for maternal age, body mass index, and parity. We found that higher levels of miR-20b-5p, miR-942-5p, miR-324-3p, miR-223-5p, and miR-127-3p in maternal serum were associated with lower odds for having a SGA vs. AGA infant, and higher levels of miR-661, miR-212-3p, and miR-197-3p were associated with higher odds for having a LGA vs. AGA infant. We also found associations between miR-483-5p, miR-10a-5p, miR-204-5p, miR-202-3p, miR-345-5p, miR-885-5p, miR-127-3p, miR-148b-3p, miR-324-3p, miR-1290, miR-597-5p, miR-139-5p, miR-215-5p, and miR-99b-5p and BWGA z-score. We also found sex-specific associations with exmiRNAs and fetal growth. Our findings suggest that exmiRNAs circulating in maternal blood at second trimester are associated with fetal growth. Validation of our findings may lead to the development of minimally-invasive biomarkers of fetal growth during pregnancy.

Bisphenol A and phthalates in utero and in childhood: association with child BMI z-score and adiposity.

OBJECTIVE: To assess the relationship between in utero and concurrent child urinary exposures to bisphenol A (BPA) and phthalates with BMI z-score, waist circumference, and sum of triceps and subscapular skinfold thickness in Mexican children. METHODS: Among participants (N=249) from the Early Life Exposure in Mexico to ENvironmental Toxicants study, we evaluated associations between maternal third trimester and concurrent urinary BPA and individual and summed phthalates metabolites (∑Di(2-ethylhexyl phthalate), ∑high molecular weight, ∑low molecular weight) with measures of weight status and adiposity in children aged 8-14 years. Linear regressions with specific-gravity corrected and natural log-transformed urinary concentrations were estimated, adjusting for covariates. Effect modification by sex was explored. RESULTS: Prenatal urinary exposure to monobenzyl phthalate (MBzP) was inversely associated with child's BMI z-score (ß=-0.21, 95%CI: -0.41, -0.02) and child urinary exposure to mono(2-ethylhexyl)phthalate (MEHP) was inversely associated with waist circumference (ß=-1.85, 95%CI: -3.36, -0.35) and sum of skinfold thicknesses (ß=-2.08, 95%CI: -3.80, -0.37) after adjusting for confounders. In the childhood exposure period, sex modified the relationships with BPA, MEHP, MBzP, monoethyl phthalate (MEP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono(2-ethyl-5-carboxypentyl) phthalate (MECPP). In girls, increased BPA exposure was positively associated with sum of skinfold thickness (ß=3.47, 95%CI: 0.05, 6.40) while increased MEHP was inversely associated with sum of skinfold thicknesses in boys (ß=-2.95, 95%CI: -5.08, -0.82); these results remained in sensitivity analyses after excluding children who had initiated pubertal development (Tanner stage >1 for pubic hair). We did not observe relationships between summed phthalates metabolites at any exposure period with outcome measures. CONCLUSION: Our results identified associations between urinary BPA and phthalates metabolites with measures of weight status and adiposity that differed by timing of exposure, sex, and pubertal status. Additional studies are needed to explore how associations may differ between those who are pre- and post-pubertal.

Antinuclear antibody prevalence in a general pediatric cohort from Mexico City: discordance between immunofluorescence and multiplex assays.

OBJECTIVE: To characterize antinuclear antibody (ANA) prevalence according to distinct assay methodologies in a pediatric cohort from Mexico City, and to further examine associations with age and sex. METHODS: Serum ANA were measured by indirect immunofluorescence assay (IFA) and multiplex immunoassay in 114 children aged 9-17 years. IFA was considered positive at a cutoff titer of ≥1:80. Agreement between assay methods was assessed by kappa statistic. Sensitivity, specificity, and 95% confidence intervals (CIs) of the multiplex were computed with IFA as the reference standard. RESULTS: Of the 114 children (mean age 14.7 [standard deviation 2.1] years; 54 [47%] female), 18 of 114 (15.8%) were ANA positive by IFA, and 11 of 114 (9.6%) by 11-antigen multiplex assay. ANA prevalence was higher in females compared with males by both of the methods (ratios 1.6-1.9 to 1). Agreement between tests was classified as slight by kappa (κ=0.177 [95% CI -0.051, 0.406]). The multiplex immunoassay had sensitivity of 22.2% (95% CI 6.4, 47.6) and specificity of 92.7% (95% CI 85.6, 97.0), and failed to capture 3 of 4 (75%) of the high-titer (≥1:1280) IFA-positives. CONCLUSION: Up to 15% of children in this general population cohort were ANA positive, with a higher rate of positivity among females according to both assay methods. Substantial discordance in ANA results was found between IFA and multiplex methods, even for high-titer IFA positives. These findings underscore the need to sufficiently account for assay characteristics when interpreting ANA test results, and support IFA as the more appropriate assay for studies of subclinical autoimmunity.

Bacterial and cytokine mixtures predict the length of gestation and are associated with miRNA expression in the cervix.

AIM: Bacterial vaginosis may lead to preterm birth through epigenetic programming of the inflammatory response, specifically via miRNA expression. METHODS: We quantified bacterial 16S rRNA, cytokine mRNA and 800 miRNA from cervical swabs obtained from 80 women at 16-19 weeks' gestation. We generated bacterial and cytokine indices using weighted quantile sum regression and examined associations with miRNA and gestational age at delivery. RESULTS & DISCUSSION: Each decile of the bacterial and cytokine indices was associated with shorter gestations (p < 0.005). The bacterial index was associated with miR-494, 371a, 4286, 185, 320e, 888 and 23a (p < 0.05). miR-494 remained significant after false discovery rate correction (q < 0.1). The cytokine index was associated with 27 miRNAs (p < 0.05; q < 0.01). CONCLUSION: Future investigation into the role of bacterial vaginosis- and inflammation-associated miRNA and preterm birth is warranted.

Mercury levels in pregnant women, children, and seafood from Mexico City.

BACKGROUND: Mercury is a global contaminant of concern though little is known about exposures in México. OBJECTIVES: To characterize mercury levels in pregnant women, children, and commonly consumed seafood samples. METHODS: Use resources of the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) birth cohorts to measure total mercury levels in archived samples from 348 pregnant women (blood from three trimesters and cord blood), 825 offspring (blood, hair, and urine) and their mothers (hair), and 91 seafood and canned tuna samples from Mexico City. RESULTS: Maternal blood mercury levels correlated across three trimesters and averaged 3.4 µg/L. Cord blood mercury averaged 4.7 µg/L and correlated with maternal blood from trimester 3 (but not trimesters 1 and 2). In children, blood, hair and urine mercury levels correlated and averaged 1.8 µg/L, 0.6 µg/g, and 0.9 µg/L, respectively. Hair mercury was 0.5 µg/g in mothers and correlated with child's hair. Mean consumption of canned tuna, fresh fish, canned sardine, and shellfish was 3.1, 2.2, 0.5, and 1.0 times per month respectively in pregnant women. Mean mercury content in 7 of 23 seafood species and 5 of 9 canned tuna brands purchased exceeded the U.S. EPA guidance value of 0.3 µg/g. CONCLUSIONS: Mercury exposures in pregnant women and children from Mexico City, via biomarker studies, are generally 3-5 times greater than values reported in population surveys from the U.S., Canada, and elsewhere. In particular, mercury levels in 29-39% of the maternal participants exceeded the biomonitoring guideline associated with the U.S. EPA reference dose for mercury.

Diarrheal diseases in children from a water reclamation site in Mexico city.

This study was conducted to assess the risk of enteric diseases among children living in a water reclamation area in Mexico City. A geographic information system was used to define eligible wells and surrounding homesteads. Sixty-five water samples from five wells were tested for fecal coliform bacteria per 100 mL (FC/100 mL) during visits to 750 eligible households; caretakers only in those dwellings with children under 5 years old were interviewed throughout repeated cross-sectional surveys, conducted during 1999-2000. Data on diarrheal diseases were obtained from 761 children during the rainy season and 732 children during the dry season; their guardians also provided information on drinking water supply, sanitation, and socioeconomic variables. The presence of indicator organisms in groundwater samples pointed to fecal pollution; bacterial indicators, however, did not predict the health risk. The rates of diarrhea were 10.7% in the dry season and 11.8% in the rainy season. Children 1 year old showed the highest rate of diarrhea during the dry season [odds ratio (OR) = 2.1 with 95% confidence interval (CI), 0.99-4.71], particularly those from households perceiving unpleasant taste of tap water (OR, 1.7; 95% CI, 0.97-2.92) and consuming vegetables washed only with water (OR, 2.2; 95% CI, 1.10-4.39). Lower risk was observed in individuals enjoying full-day water supply (OR, 0.5; 95% CI, 0.27-0.86) and a flushing toilet (OR, 0.3; 95% CI, 0.16-0.67), as well as those storing water in covered receptacles (OR, 0.3; 95% CI, 0.15-0.80). Rainy season data suggested that children from households perceiving a color to their water had a higher rate of diarrhea than did those without such complaint (OR, 1.8; 95% CI, 0.93-3.67); recent consumption of food sold by street vendors was also a significant risk factor (OR, 1.6; 95% CI, 0.98-2.87). Groundwater is at risk of contamination, as indicated by the presence of FC/100 mL. The endemic pattern of diarrhea, however, reflects mostly inadequate housing, sanitation, and water-related practices. Health protection policy must be discussed.