A review of adverse pregnancy outcomes and formaldehyde exposure in human and animal studies

Occupational factors and risk of preterm birth in nurses

OBJECTIVE

We evaluated first-trimester exposures and the risk of preterm birth in the most recent pregnancy of participants of the Nurses' Health Study II.

STUDY DESIGN

Log binomial regression was used to estimate the relative risk (RR) for preterm birth in relation to occupational risk factors, such as work schedule, physical factors, and exposures to chemicals and x-rays, adjusted for age and parity.

RESULTS

Part-time work (<or= 20 hours a week) was associated with a lower risk of preterm birth [RR, 0.7; 95% confidence interval [CI], 0.6-0.9]. Working nights was associated only with early preterm birth (< 32 weeks of gestation) (RR, 3.0; 95% CI, 1.4-6.2). Although based on only 11 exposed preterm cases, self-reported exposure to sterilizing agents was associated with an increased risk (RR, 1.9; 95% CI, 1.1-3.4).

CONCLUSION

These data suggest that night work may be related to early but not late preterm birth, whereas physically demanding work did not strongly predict risk.

Protective effects of melatonin against formaldehyde-induced oxidative damage and apoptosis in rat testes: an immunohistochemical and biochemical study

This study investigated the protective effects of melatonin against formaldehyde-induced oxidative damage and apoptosis in rat testes. A total of 21 male Wistar rats were divided into three groups. Group I was used as a control, Group II was injected every other day with formaldehyde for 1 month, whereas Group III was injected every other day with formaldehyde and melatonin for 1 month. At the end of the experimental period animals were sacrificed and the testes removed and dissected from the surrounding tissues for immunohistochemical evaluation. In addition, the levels of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) were determined. The levels of SOD and GSH-Px decreased significantly, whereas the level of MDA significantly increased in animals treated with formaldehyde compared with the controls. Apoptosis of spermatogenetic and Leydig cells of testicular tissues was observed. In contrast, rats with melatonin SOD and GSH-Px enzyme activity increased whereas MDA levels decreased with formaldehyde exposure along with apoptosis. In view of the present findings, it is suggested that melatonin treatment may prevent formaldehyde-induced oxidative damage and apoptosis in rat testes.

Effects of formaldehyde inhalation on the junctional proteins of nasal respiratory mucosa of rats

Exposure to formaldehyde, which is an organic compound, disturbs the integrity of nasal mucosa. In this study, we aimed to clarify the protein changes in the junctional complex of nasal mucosa of Wistar rats exposed to formaldehyde inhalation. The study was performed in 20 female Wistar rats. Rats were divided into two groups randomly. Control rats were allowed free access to standard rat chaw and tap water (n:10). Experimental group was exposed to formaldehyde vapor at 15ppm, 6h/day, 5 days/week for 12 weeks (n:10). Histological evaluation of the experimental model was determined by hematoxylin-eosin (HE) and periodic acid Schiff (PAS) stainings of paraffin-embedded nasal mucosa tissues and by electron microscopy. The effects of formaldehyde inhalation on the distribution of occludin, E-cadherin, and gamma-catenin were assessed by immunohistochemistry. The nasal mucosa of the experimental group was correlated with hypertrophy in goblet cell, degeneration in basal lamina, stratification of epithelium, and proliferation. Thickness of basal lamina and also local degenerative regions, vacuole increase in cytoplasmic areas, irregular forms of kinocilium and loss of sharpness in the kinocilium membrane were the findings at the ultrastructural level. The expressions of E-cadherin, occludin, gamma-catenin proteins in intercellular junctional complexes of rat nasal mucosa were also decreased in experimental group compared to control group. The findings of the present study indicated that formaldehyde vapor inhalation in the concentrations and duration of exposure used in the present experiment significantly decreased the density of structural proteins of the junctional complex in the nasoepithelium. It was suggested that, the formaldehyde inhalation could cause complete impairment of intercellular junctional complexes and disturb the tissue integrity in nasal mucosa at higher concentrations.

A review and meta-analysis of formaldehyde exposure and leukemia

Most reviews on the carcinogenicity of formaldehyde have focused on cancers of the respiratory tract because these cancer sites were thought to be most biologically plausible. However, two recent updated large industrial studies have found positive associations between some measures of formaldehyde exposure and increased leukemia, although another recent update of a large study did not find any association. We examine 18 epidemiology studies of workers exposed to formaldehyde where leukemia rates were reported. We summarize the findings across studies by using meta-analytic techniques to calculate the meta-relative risk values (mRR), confidence intervals, and heterogeneity of the risk estimates for several study characteristics. We also determine if publication or reporting biases may be affecting the estimates. We found a small increase in rate of leukemia overall among embalmers (mRR = 1.6, 95%CI 1.2-6.0), and pathologists/anatomists (mRR = 1.4, 95%CI 1.0-1.9). Industrial workers, who have been reported to have the highest formaldehyde exposures, had a mRR of 0.9 (95%CI 0.8-1.0). There was increased risk with increasing exposure in two large industrial studies, although the increased risk is one of these studies was not seen when an external comparison group is used. Also, another large industrial study with more highly exposure workers found decreased risk of leukemia among the highest exposed group. The long latency for leukemia deaths observed in the two industrial studies that reported increased risk was not consistent with a chemical carcinogen such as benzene. We found limited evidence of publication or reporting bias. On balance, these data do not provide consistent support for a relationship between formaldehyde exposure and leukemia risk.

Risk factors for low birth weight: a review

Low birth weight (LBW) is one of the main predictors of infant mortality. The global incidence of LBW is around 17%, although estimates vary from 19% in the developing countries (countries where it is an important public health problem) to 5-7% in the developed countries. The incidence in Spain in the decade 1980-1989 was about 5.7%. LBW is generally associated with situations in which uterine malnutrition is produced due to alterations in placental circulation. There are many known risk factors, the most important of which are socio-economic factors, medical risks before or during gestation and maternal lifestyles. However, although interventions exist to prevent many of these factors before and during pregnancy, the incidence of LBW has not decreased.

Maternal exposure to low-level air pollution and pregnancy outcomes: a population-based study

BACKGROUND

Recent reports have shown that air pollution may increase the risk of adverse birth outcomes. We have evaluated the relationship between ambient air pollution and the occurrence of low birth weight and preterm delivery using routinely collected data in Lithuania.

METHODS

This epidemiological study comprised all singleton newborns (N = 3,988), born to women in 1998, who resided in the City of Kaunas. Birth data and information on maternal characteristics were obtained from the Lithuanian National Birth Register. To estimate residential exposure levels, we used measurements of ambient nitrogen dioxide (NO2) and formaldehyde, which were collected at 12 monitoring posts. Multivariate logistic regression was used to estimate the effect that each pollutant would have on low birth weight (LBW) and premature birth while controlling for potential confounders.

RESULTS

Adjusted odds ratios (OR) for LBW increased with increasing formaldehyde exposure (OR2nd tertile = 1.86, 95% CI 1.10-3.16; OR3rd tertile = 1.84, 95% CI 1.12-3.03). Adjusted ORs of preterm birth for the medium and high NO2 tertile exposures were OR = 1.14 (95% CI 0.77-1.68) and OR = 1.68 (95% CI 1.15-2.46), respectively. The risk of preterm birth increased by 25% (adjusted OR = 1.25, 95% CI 1.07-1.46) per 10 microg/m3 increase in NO2 concentrations. An analysis by trimester showed that pregnancy outcomes were associated with first-trimester exposure to air pollutants. However, there were no significant relationships in other pregnancy periods between preterm birth and exposure to formaldehyde or between LBW and NO2 exposure.

CONCLUSION

Our findings suggest that in the City of Kaunas there might be a relationship between maternal exposure to ambient formaldehyde and the risk of LBW, as well as between NO2 exposure and the risk of preterm birth.