Prenatal maternal stress and atopic diseases in the child: a systematic review of observational human studies.

BACKGROUND: A growing number of studies suggest that maternal stress during pregnancy promotes atopic disorders in the offspring. This is the first systematic review to address prenatal maternal stress (PNMS) and the subsequent risk of atopy-related outcomes in the child. METHODS: The review was performed in accordance to the PRISMA criteria. We searched and selected studies in PubMed, Scopus, Embase and PsychINFO until November 2014. RESULTS: Sixteen (with 25 analyses) of 426 identified articles met the review criteria. Five main PNMS exposures (negative life events, anxiety/depression, bereavement, distress and job strain) and five main atopic outcomes (asthma, wheeze, atopic dermatitis, allergic rhinitis and IgE) were assessed across the studies. Overall, 21 of the 25 analyses suggested a positive association between PNMS and atopic outcomes. Of the 11 exposure-response analyses reported, six found statistically significant trends. CONCLUSION: This systematic review suggests a relationship between maternal stress during pregnancy and atopic disorders in the child. However, the existing studies are of diverse quality. The wide definitions of often self-reported stress exposures imply a substantial risk for information bias and false-positive results. Research comparing objective and subjective measures of PNMS exposure as well as objective measures for atopic outcome is needed.

Ambient and at-the-ear occupational noise exposure and serum lipid levels.

OBJECTIVES: Occupational and residential noise exposure has been related to increased risk of cardiovascular disease. Alteration of serum lipid levels has been proposed as a possible causal pathway. The objective of this study was to investigate the relation between ambient and at-the-ear occupational noise exposure and serum levels of total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, and triglycerides when accounting for well-established predictors of lipid levels. METHODS: This cross-sectional study included 424 industrial workers and 84 financial workers to obtain contrast in noise exposure levels. They provided a serum sample and wore portable dosimeters that every 5-s recorded ambient noise exposure levels during a 24-h period. We extracted measurements obtained during work and calculated the full-shift mean ambient noise level. For 331 workers who kept a diary on the use of a hearing protection device (HPD), we subtracted 10 dB from every noise recording obtained during HPD use and estimated the mean full-shift noise exposure level at the ear. RESULTS: Mean ambient noise level was 79.9 dB (A) [range 55.0-98.9] and the mean estimated level at the ear 77.8 dB (A) [range 55.0-94.2]. Ambient and at-the-ear noise levels were strongly associated with increasing levels of triglycerides, cholesterol-HDL ratio, and decreasing levels of HDL-cholesterol, but only in unadjusted analyses that did not account for HPD use and other risk factors. CONCLUSION: No associations between ambient or at-the-ear occupational noise exposure and serum lipid levels were observed. This indicates that a causal pathway between occupational and residential noise exposure and cardiovascular disease does not include alteration of lipid levels.

Morphological diversity of Paramoeba perurans trophozoites and their interaction with Atlantic salmon, Salmo salar L., gills.

Amoebic gill disease (AGD) caused by the ectoparasite Paramoeba perurans affects several cultured marine fish species worldwide. In this study, the morphology and ultrastructure of P. perurans in vitro and in vivo was investigated using scanning and transmission electron microscopy (SEM and TEM, respectively). Amoebae cultures contained several different morphologies ranging from a distinct rounded cell structure and polymorphic cells with pseudopodia of different lengths and shapes. SEM studies of the gills of AGD-affected Atlantic salmon, Salmo salar L., revealed the presence of enlarged swellings in affected gill filaments and fusion of adjacent lamellae. Spherical amoebae appeared to embed within the epithelium, and subsequently leave hemispherical indentations with visible fenestrations in the basolateral surface following their departure. These fenestrated structures corresponded to the presence of pseudopodia which could be seen by TEM to penetrate into the epithelium. The membrane-membrane interface contained an amorphous and slightly fibrous matrix. This suggests the existence of cellular glycocalyces and a role for extracellular products in mediating pathological changes in amoebic gill disease.

Individual and work-unit measures of psychological demands and decision latitude and the use of antihypertensive medication.

PURPOSE: To analyse whether psychological demands and decision latitude measured on individual and work-unit level were related to prescription of antihypertensive medication. METHODS: A total of 3,421 women and 897 men within 388 small work units completed a questionnaire concerning psychological working conditions according to the job strain model. Mean levels of psychological demands and decision latitude were computed for each work unit to obtain exposure measures that were less influenced by reporting bias. Dispensed antihypertensive medication prescriptions were identified in The Danish National Prescription Registry. Odds ratios (OR) comparing the highest and lowest third of the population at individual and work-unit level, respectively, were estimated by multilevel logistic regression adjusted for confounders. Psychological demands and decision latitude were tested for interaction. Supplementary analyses of 21 months follow-up were conducted. RESULTS: Among women, increasing psychological demands at individual (adjusted OR 1.54; 95 % CI 1.02-2.33) and work-unit level (adjusted OR 1.41; 95 % CI 1.04-1.90) was significantly associated with purchase of antihypertensive medication. No significant association was found for decision latitude. Follow-up results supported an association with psychological demands but they were not significant. All results for men showed no association. Psychological demands and decision latitude did not interact. CONCLUSION: High psychological work demands were associated with the purchase of prescribed antihypertensive medication among women. This effect was present on both the work-unit and the individual level. Among men there were no associations. The lack of interaction between psychological demands and decision latitude did not support the job strain model.

The norepinephrine transporter gene is a candidate gene for panic disorder.

Panic disorder (PD) is an anxiety disorder characterized by recurrent panic attacks with a lifetime prevalence of 4.7%. Genetic factors are known to contribute to the development of the disorder. Several lines of evidence point towards a major role of the norepinephrine system in the pathogenesis of PD. The SLC6A2 gene is located on chromosome 16q12.2 and encodes the norepinephrine transporter (NET), responsible for the reuptake of norepinephrine into presynaptic nerve terminals. The aim of the present study was to analyze genetic variants located within the NET gene for association with PD. The case-control sample consisted of 449 patients with PD and 279 ethnically matched controls. All cases fulfilled the ICD-10 diagnostic criteria for PD. Genotyping was performed using the Sequenom platform (Sequenom, Inc, San Diego, USA). To test for allelic and haplotypic association, the PLINK software was used, and COMBASSOC was applied to test for gene-wise association. After quality control 29 single nucleotide polymorphisms (SNPs) spanning the gene-region were successfully analyzed. Seven SNPs located within the 5' end of the gene were significantly associated with PD. Furthermore, the NET gene showed overall evidence for association with the disease (P = 0.000035). In conclusion, the present study indicates that NET could be a susceptibility gene for PD.

Inhibin B as a serum marker of spermatogenesis: correlation to differences in sperm concentration and follicle-stimulating hormone levels. A study of 349 Danish men.

Recent studies have focused on reproductive health of men in the general population. However, semen samples are difficult to obtain within sampling frames that allow comparisons. Blood samples are easier to obtain than ejaculates. Therefore, serum biomarkers of spermatogenesis are of major interest for population studies. FSH has previously been used as a marker of spermatogenesis, although it is also influenced by the hypothalamus. Serum inhibin B was recently suggested as a possible, more direct serum marker of spermatogenesis in men with testicular disorders. In a Danish nationwide collaborative study, we found an unexpected difference in semen concentration between two groups of men recruited from two different centres. We, therefore, analyzed reproductive hormones in blood, including inhibin B, to test whether the observed difference in semen concentration was reflected in the reproductive hormones. From 1992 to 1995, a total of 430 men, 20-35 yr old, who lived with a partner and who had not previously attempted to achieve a pregnancy, were recruited. The couples were enrolled into the study in one of two centres (centre A, n = 231; and centre B, n = 199) when they discontinued birth control. At enrollment, they provided a semen sample (n = 419), and a blood sample was drawn (n = 349). The semen analysis was performed in accordance with the WHO 1992 guidelines, and interlaboratory differences were tested. Inhibin B was measured in an enzyme immunometric assay, which has previously been described. All blood samples were analyzed in the same laboratory. Median sperm concentration and the percentage of morphologically normal spermatozoa were significantly higher among men from centre A (56.0 mill/mL and 42.5%), compared with men from centre B (44.8 mill/mL and 39%). Men from centre B had a significantly higher median FSH (3.42 IU/L) and a lower inhibin B (186 pg/mL) than men from centre A (3.21 IU/L and 209 pg/mL). The differences persisted after control for potentially confounding variables. A significant correlation was found between the cubic root-transformed serum FSH and inhibin B levels (r = -0.61, P < 0.001), between the cubic root-transformed serum FSH and sperm concentration (r = -0.40, P < 0.001), and between the cubic root-transformed inhibin B and sperm concentration (r = 0.38, P < 0.001). The predictive power of detecting sperm counts below 20 mill/mL among men who's inhibin B and FSH both were below 80 pg/mL and above 10 IU/L, respectively, was 100%. The unexpected significant difference in semen concentration between two groups of normal Danish men was probably caused by differences in sampling procedures in the two centres where the men were recruited, rather than geographical differences. However, similar differences in serum levels of inhibin B and FSH between centres were found. These findings suggest that a real difference in spermatogenic potential between the two groups of men existed. We suggest that serum inhibin B, in future population studies on male reproductive health, may serve as a new marker of spermatogenesis, in addition to sperm concentration and serum FSH.

Fertility of Danish battery workers exposed to lead.

BACKGROUND: Inorganic lead may impair male fecundity through its action on the germinal epithelium, the endocrine system or both, but information on possible impact on fertility in exposed populations is limited. METHODS: Fertility was examined in 1349 male battery plant employees and in 9596 reference company employees over a follow-up of 25,949 and 183,414 person years respectively. The cohorts were identified by records in a national pension fund and information on births was obtained from the Danish Population Register. In a subset of the battery worker cohort, the average level of lead in blood was 35.9 micrograms/dl (4639 blood samples on 1654 person years in 400 workers; SD 13.0; range 3-125). The birth rate was analysed by logistic regression on occupational exposure and several extraneous determinants (age, parity, calendar year, and previous children). RESULTS: The birth-rate was not reduced in years at risk from exposure to lead in comparison with years not-at-risk; either in comparison with not-at-risk years within the battery plant cohort (odds ratio [OR] = 0.997, 95% confidence interval [CI]: 0.88-1.13), or in comparison with the external reference population (OR = 0.983, 95% CI: 0.87-1.11). CONCLUSIONS: Inorganic lead seems not to impair fertility among Danish battery workers. This finding does not rule out that the time taken to achieve a pregnancy is increased among battery workers because most pregnancies in Denmark are planned.

PIP: This study examined the effects of exposure to lead among battery workers on fertility in Denmark. The research methods were based on an earlier study among metal workers. The sample population included a cohort of 1349 men born in 1940 or after who worked at 3 Danish battery plants between April 1, 1964 and December 31, 1992. The plants were located in different parts of the country. The control population included 9596 workers from 86 Danish manufacturing steel, wooden boat, and plastics products companies. All workers were considered to be exposed to lead during their period of employment. Biological monitoring of blood lead levels (BLLs) was conducted during 1983-88 among 400 workers, or 4639 blood samples. The average BLL was 39.2 mcg/dl. Average BLLs declined slightly during follow-up. More samples were taken from workers with high BLLs. Findings indicate that employment at a Danish battery plant was not associated with any change in fertility, as measured by the birthrate, during either the years of employment or subsequent years. There was no indication that long-term exposure was related to reduced fertility. Reduced fecundity, which is correlated with exposure to lead, may not necessarily result in reduced fertility. Reduced fecundity may be counteracted by an increased number of menstrual cycles exposed to sperm. The most important factors that mediate between reduced fecundity and reduced fertility are the extent of reproductive impairment, the number of desired children, and the timing of initiation of sexual activity during the reproductive period. Several European countries are involved in studies to determine the impact on time-to-pregnancy and semen quality in lead-exposed populations.

Sperm chromatin damage impairs human fertility. The Danish First Pregnancy Planner Study Team.

OBJECTIVE: To examine the relationship between sperm chromatin defects, evaluated by the flow cytometric (FCM) sperm chromatin structure assay (SCSA), and the probability of a pregnancy in a menstrual cycle (fecundability). DESIGN: Follow-up study. SETTING: The Section of Toxicology and Biomedical Sciences, ENEA Casaccia, Rome, Italy, and the Department of Occupational Medicine, Aarhus University Hospital, Aarhus, Denmark. PATIENT(S): Two hundred fifteen Danish first pregnancy planners with no previous knowledge of their fertility capability. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Semen samples were collected at enrollment to measure semen volume, sperm concentration, motility, and morphology (by microscopy), as well as chromatin susceptibility to in situ, acid-induced partial denaturation by the FCM SCSA. Time to pregnancy was evaluated during a 2-year follow-up period. Demographic, medical, reproductive, occupational, and lifestyle data were collected by questionnaire. Fecundability was correlated with SCSA-derived parameters. RESULT(S): Fecundability declines as a function of the percentage of sperm with abnormal chromatin and becomes small when aberrant cells are >40%. CONCLUSION(S): Optimal sperm chromatin packaging seems necessary for full expression of the male fertility potential. The SCSA emerged as a predictor of the probability to conceive in this population-based study.

Menstrual cycle pattern and fertility: a prospective follow-up study of pregnancy and early embryonal loss in 295 couples who were planning their first pregnancy.

OBJECTIVE: To characterize how the menstrual cycle pattern relates to fertility regardless of potential biases caused by inappropriate coital timing during the menstrual cycle or early embryonal loss. DESIGN: Prospective follow-up study. SETTING: Healthy couples recruited throughout Denmark. PATIENT(S): Two hundred ninety-five couples who were planning their first pregnancy were followed up from the discontinuation of birth control until a pregnancy was recognized within six menstrual cycles. Early embryonal losses were detected by changes in urinary hCG levels. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The probability of pregnancy occurring within one menstrual cycle (fecundity). RESULT(S): In women who had a cycle length that differed by >10 days from the usual cycle length, fecundity was approximately 25% that of women who had no variation (odds ratio 0.25, 95% confidence interval 0.09-0.68). When the combined effect of cycle variation and cycle length was assessed, cycle variation was a persistent strong predictor of fecundity. CONCLUSION(S): The mechanisms of the present findings probably are female functional disturbances in ovulation, conception, implantation, or sustained pregnancy, linked with variable menstrual cycle length. Thus, identification of medical and environmental causes of abnormal menstrual cycle patterns may provide clues to the causes of infertility. Moreover, the menstrual cycle pattern also should be taken into consideration in the clinical decision-making process.

Distress and reduced fertility: a follow-up study of first-pregnancy planners.

OBJECTIVE: To assess the effect of psychological distress on time to first pregnancy. DESIGN: A follow-up study of time to pregnancy with prospective data on distress, with controlling for potential confounding variables. SETTING: Two university hospitals. PATIENT(S): Danish couples (n = 430) who were planning their first pregnancy and had no previous reproductive experience were followed for six menstrual cycles. Psychological distress was measured in each menstrual cycle by the General Health Questionnaire. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): A clinically recognized pregnancy or a biochemical pregnancy detected in urine samples from each period of vaginal bleeding. RESULT(S): For cycles with the highest distress score (General Health Questionnaire score >80th percentile), the probability of conception per cycle was 12.8%, compared with 16.5% in other cycles (adjusted odds ratio [OR] 0.6; 95% confidence interval [CI] 0.4-1.0). The effect of distress was found almost exclusively among women with long menstrual cycles (OR 0.1; 95% CI 0.01-0.4 and OR 0.9; 95% CI 0.5-1.4 for women with cycles of > or =35 and <35 days, respectively). An increased incidence of early embryonal loss was also found among highly distressed women with long cycles, but was based on a small number of observations. CONCLUSION(S): Psychological distress may be a risk factor for reduced fertility in women with long menstrual cycles.

Surveillance of noise exposure in the Danish workplace: a baseline survey.

AIMS: To evaluate an epidemiological approach to a national noise hazard surveillance strategy, and report current exposure levels in the Danish workplace. METHODS: A study base of 840 companies in 10 selected high risk industries in the largest county in Denmark was identified from a national register. Noise exposure was measured among manual workers recruited from a random sample of workplaces in each industry. For reference, financial companies and a sample of residents were investigated according to the same protocol. The A-weighted equivalent sound level (L(Aeq)) for a full shift was measured by portable dosimeters worn by 830 workers employed at 91 workplaces (67% of 136 eligible companies). RESULTS: The epidemiological design proved feasible and established a baseline for future noise surveillance. Substantial resources were needed to motivate workplaces to enlist and the final participation rate was less than optimal (66.9%). The L(Aeq (8)) values in the selected industries were highly elevated (mean 83.7 dB(A) (95% CI 83.3 to 84.1) in comparison with residents and office workers (mean 69.9 dB(A), 95% CI 68.8 to 71.0). Some 50% of the workers were exposed to more than 85 dB(A) and some 20% to more than 90 dB(A) in several industries. CONCLUSION: Noise levels in Danish high risk industries remain high. A substantial proportion of workers are exposed to noise levels above the current threshold limit of 85 dB(A). Ongoing surveillance of noise exposure using full shift dosimetry of workers in random samples of workplaces most at risk to high noise levels may help reinforce preventive measures. Such a programme would benefit from compulsory workplace participation.

Caffeine intake and fecundability: a follow-up study among 430 Danish couples planning their first pregnancy.

Fecundability has been defined as the ability to achieve a recognized pregnancy. Several studies on caffeine and fecundability have been conducted but have been inconclusive. This may be explained partly by lack of stratification by smoking. Furthermore, few researchers have tried to separate the effect of caffeine from different sources (coffee, tea, cola, and chocolate). Clearly, the relationship between caffeine and fecundability needs further research, given the high prevalence of caffeine intake among women of childbearing age. We examined the independent and combined effects of smoking and caffeine intake from different sources on the probability of conception. From 1992 to 1995, a total of 430 couples were recruited after a nationwide mailing of a personal letter to 52,255 trade union members who were 20 to 35 years old, lived with a partner, and had no previous reproductive experience. At enrollment and in six cycles of follow-up, both partners filled out a questionnaire on different factors including smoking habits and their intake of coffee, tea, chocolate, cola beverages, and chocolate bars. In all, 1596 cycles and 423 couples were included in the analyses. The cycle-specific association between caffeine intake and fecundability was analyzed in a logistic regression model with the outcome at each cycle (pregnant or not pregnant) in a Cox discrete model calculating the fecundability odds-ratio (FR). Compared to nonsmoking women with caffeine intake less than 300 mg/d, nonsmoking women who consumed 300 to 700 mg/d caffeine had a FR of 0.88 [95% confidence interval (CI) 0.60-1.31], whereas women with a higher caffeine intake had a FR = 0.63 (95% CI 0.25-1.60) after adjusting for female body mass index and alcohol intake, diseases of the female reproductive organs, semen quality, and duration of menstrual cycle. No dose-response relationship was found among smokers. Among males, the same decline in point estimates of the FR was present. Smoking women whose only source of caffeine was coffee (>300 mg/d) had a reduced fecundability odds-ratio (FR = 0.34; 95% CI 0.12-0.98). An interaction between caffeine and smoking is biologically plausible, and the lack of effect among smokers may be due to faster metabolism of caffeine. Our findings suggest that especially nonsmoking women who wish to achieve a pregnancy might benefit from a reduced caffeine intake.

PIP: The independent and combined effects of smoking and caffeine intake from different sources on fecundability were assessed in a national survey of 423 Danish couples. Couples were recruited to the study in 1992-95 through a mailing to 52,255 female trade union members seeking women who were 20-35 years old, lived with a partner, had no previous pregnancies, and intended to discontinue contraception in order to become pregnant. A total of 1596 cycles were included in the 6-month study and the cycle-specific association between caffeine intake and fecundability was analyzed in a logistic regression model with the outcome (pregnant, not pregnant) in a Cox discrete model. Compared with nonsmoking women with a caffeine intake less than 300 mg/day, nonsmoking women who consumed 300-700 mg/day of caffeine had a fecundability odds ratio (FR) of 0.88 (95% confidence interval (CI), 0.60-1.31), while those with a higher consumption had an FR of 0.63 (95% CI, 0.25-1.60), after adjustments for body mass index, alcohol intake, diseases of the female reproductive organs, semen quality, and duration of the menstrual cycle. No such dose-response relationship was detected among smokers. The same decline in point estimates of the FR was present was males. Smoking women whose only source of caffeine was coffee (over 300 mg/day) had a reduced FR (0.34; 95% CI, 0.12-0.98). The lack of adverse effect among smokers may be due to faster metabolism and clearance of caffeine. Overall, these findings indicate that nonsmoking women who wish to achieve pregnancy should consider reducing their caffeine intake.

Semen quality and sex hormones with reference to metal welding.

Welding may involve hazards to the male reproductive system, but previous studies of semen quality have produced inconsistent results. We studied the effects of welding on markers of semen quality in a Danish nationwide sample of 430 first-time pregnancy planners without earlier reproductive experience. Couples were recruited among members of the union of metal workers and three other trade unions and were followed from termination of birth control until pregnancy for a maximum of six menstrual cycles. The males provided semen samples in each cycle. Median sperm density for welders was 56 x 10(6)/mL (52.5 x 10(6)/mL and 50.0 x 10(6)/mL in two reference groups). No statistically significant differences attributable to welding were found in proportions of morphologically normal sperm, sperm motility assessed by computer-aided sperm analysis, or sex hormones (testosterone, follicle-stimulating hormone, and luteinizing hormone). These negative findings may not apply to populations with high-level exposure to welding fume or to welders exposed to other putative hazards, e.g., heat.

A follow-up study of environmental and biologic determinants of fertility among 430 Danish first-pregnancy planners: design and methods.

This paper presents design and methods of a follow-up study of fecundability (defined as the probability of conception during one menstrual cycle) in first-pregnancy planners. We recruited 430 couples by postal letter among 52,255 members of four trade unions. Couples without earlier reproductive experience were enrolled when they discontinued contraception and were followed in six complete menstrual cycles or until a pregnancy was recognized. Data included daily recordings of coitus and menstrual bleeding. Blood, semen, and urine specimens were collected to assess endocrine profile, semen quality, occult embryonal loss, and occupational exposures. Information was obtained about 1661 menstrual cycles (94% of expected). The proportion of couples obtaining a clinical pregnancy during 6 months of follow-up was 65%, and the average probability to obtain a pregnancy across all cycles was 16% (95% CI 14-18%). Among all conceptions the proportion of early embryonal loss was 17% (95% CI 12-22%). This study demonstrates the feasibility of a prospective study of fertility and that the established study base can provide useful information on environmental risk to subfertility.

A follow-up study of male exposure to welding and time to pregnancy.

The aim of this study was to estimate whether male welding has an impact on couple fecundability (the probability of conceiving in a menstrual cycle). A sample of Danish couples without previous reproductive experience was recruited nationwide by postal letters to members of the union of metal workers and three other trade unions. Among 430 included couples, 201 males were metal workers and 130 were welders. The couples were followed for a maximum of six menstrual cycles from termination of birth control until a clinical pregnancy was detected. Compared with nonwelding metal workers the fecundability odds ratio (OR) of male exposure to welding was 0.86 (95% confidence interval [CI] 0.58-1.28). An interaction between male smoking and welding was found; within smokers the OR for welding was 0.40 (95% CI 0.17-0.95) and within nonsmokers it was 1.22 (95% CI 0.74-1.99). Previous welding exposure was negatively related to fecundability among smokers (OR 0.84 per year with mild steel welding, OR 0.76 per year with stainless steel welding). No significant results were found when comparing with an external group of nonmetal workers. Decreased fecundability among smoking welders attributable to both current and previous welding exposure is possible, but these findings were the results of subanalyses that were not part of the a priori hypothesis.

Mortality of short-term workers in two international cohorts.

The purpose of this study was to compare the pattern of mortality of blue-collar workers employed less and more than 1 year in the man-made vitreous fiber (MMVF) and the reinforced plastic industries, the latter group being exposed to styrene. We conducted an analysis among 21,784 workers with less than 1 year of employment (short-term workers) and 19,117 workers with 1 or more years of employment (long-term workers) employed in eight European countries. We conducted analyses based on external as well as internal comparisons. In both cohorts, the standardized mortality ratio for all causes among short-term workers was approximately 40% higher, compared with that for longer-term workers. In internal comparisons, the difference was reduced to 9% in the MMVF cohort and 11% in the styrene cohort. Workers with less than 1 month of employment displayed an increased mortality in both cohorts and in most countries. The increased mortality among short-term workers was not concentrated shortly after they quit employment. In both cohorts, short-term workers had a higher mortality from external causes, while little difference was seen in mortality from ischemic heart disease and malignant neoplasms. Although extra-occupational factors may contribute to increase the mortality of short-term workers and, in particular, of those employed for less than 1 month, the difference observed in analyses adjusted for characteristics of employment suggested a relatively small difference in mortality from most causes.

Incidence of lymphohematopoietic malignancies among styrene-exposed workers of the reinforced plastics industry.

OBJECTIVES: The goal of this study was to determine the risk of lymphohematopoietic malignancies for workers exposed to styrene. METHODS: This was a historical cohort study. The observed numbers of newly diagnosed cases of lymphohematopoietic malignancies in the study population were compared with expected numbers based on the national rates. The study took place in the Danish reinforced plastic industry, in which high exposure levels of styrene occur frequently in an environment free of most other suspected carcinogens. Altogether 36,525 male employees of 386 companies producing reinforced plastics and 14,254 nonstyrene exposed employees of similar industries were studied. RESULTS: An insignificantly increased standardized incidence ratio (SIR) of 1.22 [95% confidence interval (95% CI) 0.88-1.65] was found for leukemia among all employees of the reinforced plastics industry. Workers employed in the 1960s (the period with the highest recorded styrene levels) or in companies with the highest exposure probability showed increased SIR values of 1.54 (95% CI 1.04-2.19) and 1.38 (95% CI 0.75-2.32), respectively. Both estimates increased when a 10-year latency period was considered. CONCLUSIONS: An increased risk of leukemia was shown for workers in the early phase of the reinforced plastics industry in Denmark. If this association is not due to chance or confounding, the most likely cause is styrene exposure.