Maternal weight gain in excess of pregnancy guidelines is related to daughters being overweight 40 years later

BACKGROUND

Exceeding the Institute of Medicine guidelines for pregnancy weight gain increases childhood and adolescent obesity. However, it is unknown if these effects extend to midlife.

OBJECTIVE

We sought to determine if exceeding the Institute of Medicine guidelines for pregnancy weight gain increases risk of overweight/obesity in daughters 40 years later.

STUDY DESIGN

This cohort study is based on adult offspring in the Child Health and Development Studies and the Collaborative Perinatal Project pregnancy cohorts originally enrolled in the 1960s. In 2005 through 2008, 1035 daughters in their 40s were recruited to the Early Determinants of Mammographic Density study. We classified maternal pregnancy weight gain as greater than vs less than or equal to the 2009 clinical guidelines. We used logistic regression to compare the odds ratios of daughters being overweight/obese (body mass index [BMI] ≥25) at a mean age of 44 years between mothers who did not gain or gained more than pregnancy weight gain guidelines, accounting for maternal prepregnant BMI, and daughter body size at birth and childhood. We also examined potential family related confounding through a comparison of sisters using generalized estimating equations, clustered on sibling units and adjusted for maternal age and race.

RESULTS

Mothers who exceeded guidelines for weight gain in pregnancy were more likely to have daughters who were overweight/obese in their 40s (odds ratio [OR], 3.4; 95% confidence interval {CI}, 2.0-5.7). This magnitude of association translates to a relative risk (RR) increase of 50% (RR = 1.5; 95% CI, 1.3-1.6). The association was of the same magnitude when examining only the siblings whose mother exceeded guidelines in 1 pregnancy and did not exceed the guidelines in the other pregnancy. The association was stronger with increasing maternal prepregnancy BMI (P trend < .001). Compared to mothers with BMI <25 who did not exceed guidelines, the relative risks (RR) for having an overweight/obese adult daughter were 1.3 (95% CI, 1.1-1.7), 1.7 (95% CI, 1.4-2.1) and 1.8 (95% CI, 1.5-2.1), respectively, if mothers exceeded guidelines and their prepregnancy BMI was <25, overweight (BMI 25-<30), or obese (BMI >30). This pattern held irrespective of daughters' weight status at birth, at age 4 years, or at age 20 years.

CONCLUSION

Our findings support that obesity prevention before pregnancy and strategies to maintain weight gain during pregnancy within the IOM guidelines might reduce the risk of being overweight in midlife for the offspring.

Is grand-parental smoking associated with adolescent obesity? A three-generational study

BACKGROUND/OBJECTIVES

Data from previous studies consistently suggest that maternal smoking is positively associated with obesity later in life. Whether this association persists across generations is unknown. We examined whether grand-parental smoking was positively associated with overweight status in adolescence.

SUBJECT/METHODS

Participants were grandmother-mother-child triads in the Nurses' Health Study II (NHS II), the Nurses Mothers' Cohort Study and the Growing up Today Study (GUTS). Grandmothers provided information on their and their partner's smoking during pregnancy with the child's mother. Information on child's weight and height at ages 12 (N=3094) and 17 (N=3433) was obtained from annual or biennial GUTS questionnaires. We used logistic regression to estimate the odds ratios (ORs) of being overweight or obese, relative to normal weight.

RESULTS

Grand-maternal smoking during pregnancy was not associated with overweight status in adolescence. After adjusting for covariates, the OR of being overweight or obese relative to normal weight at age 12 years in girls whose grandmothers smoked 15+ cigarettes daily during pregnancy was 1.21 (95% confidence interval (CI) 0.74-1.98; P(trend)=0.31) and 1.07 (0.65-1.77; P(trend)=0.41) in boys. Grand-paternal smoking during pregnancy was associated with being overweight or obese at age 12 in girls only, but not at age 17 for either sex: the OR for being overweight or obese at age 12 was 1.38 (95% CI 1.01-1.89; P(trend)=0.03) in girls and 1.31 (95% CI 0.97-1.76; P(trend)=0.07) in boys. Among children of non-smoking mothers, the OR for granddaughter obesity for grand-paternal smoking was attenuated and no longer significant (OR 1.28 (95% CI 0.87-1.89; P(trend)=0.18)).

CONCLUSIONS

Our findings suggest that the association between maternal smoking and offspring obesity may not persist beyond the first generation. However, grand-paternal smoking may affect the overweight status of the granddaughter, likely through the association between grand-paternal smoking and maternal smoking.

Sugar-sweetened beverage consumption and age at menarche in a prospective study of US girls

STUDY QUESTION

Is sugar-sweetened beverage (SSB) consumption associated with age at menarche?

SUMMARY ANSWER

More frequent SSB consumption was associated with earlier menarche in a population of US girls.

WHAT IS KNOWN ALREADY

SSB consumption is associated with metabolic changes that could potentially impact menarcheal timing, but direct associations with age at menarche have yet to be investigated.

STUDY DESIGN, SIZE, DURATION

The Growing up Today Study, a prospective cohort study of 16 875 children of Nurses' Health Study II participants residing in all 50 US states. This analysis followed 5583 girls, aged 9-14 years and premenarcheal at baseline, between 1996 and 2001. During 10 555 person-years of follow-up, 94% (n = 5227) of girls reported their age at menarche, and 3% (n = 159) remained premenarcheal in 2001; 4% (n = 197) of eligible girls were censored, primarily for missing age at menarche.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Cumulative updated SSB consumption (composed of non-carbonated fruit drinks, sugar-sweetened soda and iced tea) was calculated using annual Youth/Adolescent Food Frequency Questionnaires from 1996 to 1998. Age at menarche was self-reported annually. The association between SSB consumption and age at menarche was assessed using Cox proportional hazards regression.

MAIN RESULTS AND THE ROLE OF CHANCE

More frequent SSB consumption predicted earlier menarche. At any given age between 9 and 18.5 years, premenarcheal girls who reported consuming >1.5 servings of SSBs per day were, on average, 24% more likely [95% confidence interval (CI): 13, 36%; P-trend: <0.001] to attain menarche in the next month relative to girls consuming ≤2 servings of SSBs weekly, adjusting for potential confounders including height, but not BMI (considered an intermediate). Correspondingly, girls consuming >1.5 SSBs daily had an estimated 2.7-month earlier menarche (95% CI: -4.1, -1.3 months) relative to those consuming ≤2 SSBs weekly. The frequency of non-carbonated fruit drink (P-trend: 0.03) and sugar-sweetened soda (P-trend: 0.001), but not iced tea (P-trend: 0.49), consumption also predicted earlier menarche. The effect of SSB consumption on age at menarche was observed in every tertile of baseline BMI. Diet soda and fruit juice consumption were not associated with age at menarche.

LIMITATIONS, REASONS FOR CAUTION

Although we adjusted for a variety of suspected confounders, residual confounding is possible. We did not measure SSB consumption during early childhood, which may be an important window of exposure.

WIDER IMPLICATIONS OF THE FINDINGS

More frequent SSB consumption may predict earlier menarche through mechanisms other than increased BMI. Our findings provide further support for public health efforts to reduce SSB consumption.

STUDY FUNDING/COMPETING INTERESTS

The Growing up Today Study is supported by grant R03 CA 106238. J.L.C. was supported by the Breast Cancer Research Foundation; Training Grant T32ES007069 in Environmental Epidemiology from the National Institute of Environmental Health Sciences, National Institutes of Health; and Training Grant T32HD060454 in Reproductive, Perinatal and Pediatric Epidemiology from the National Institute of Child Health and Human Development, National Institutes of Health. A.L.F. is supported by the American Cancer Society, Research Scholar Grant in Cancer Control. K.B.M. was supported in part by the National Cancer Institute at the National Institutes of Health (Public Health Service grants R01CA158313 and R03CA170952). There are no conflicts of interest to declare.

Development and evaluation of a short 24-h food list as part of a blended dietary assessment strategy in large-scale cohort studies

BACKGROUND/OBJECTIVES

The validity of dietary assessment in large-scale cohort studies has been questioned. Combining data sources for the estimation of usual intake in a blended approach may enhance the validity of dietary measurement. Our objective was to develop a web-based 24-h food list for Germany to identify foods consumed during the previous 24 h and to evaluate the performance of the new questionnaire in a feasibility study.

SUBJECTS/METHODS

Available data from the German National Nutrition Survey II were used to develop a finite list of food items. A total of 508 individuals were invited to fill in the 24-h food list via the Internet up to three times during a 3-6-month time period. In addition, participants were asked to evaluate the questionnaire using a brief online evaluation form.

RESULTS

In total, 246 food items were identified for the 24-h food list, reflecting >75% variation in intake of 27 nutrients and four major food groups. Among the individuals invited, 64% participated in the feasibility study. Of these, 100%, 85% and 68% of participants completed the 24-h food list one, two or three times, respectively. The average time needed to complete the questionnaire was 9 min, and its acceptability by participants was rated as high.

CONCLUSIONS

The 24-h food list represents a promising new dietary assessment tool that can be used as part of a blended approach combining multiple data sources for valid estimation of usual dietary intake in large-scale cohort studies.

Prenatal vitamin intake during pregnancy and offspring obesity

Background/Objectives

In animal studies, exposure to multi-vitamins may be associated with obesity in the offspring; however, data in humans is sparse. We therefore examined the association between prenatal vitamin intake during pregnancy and offspring obesity.

Subjects/Methods

We investigated the association between prenatal vitamin intake and obesity among 29 160 mother-daughter dyads in the Nurses’ Health Study II. Mothers of participants provided information on prenatal vitamin use during pregnancy with the nurse daughter. Information on body fatness at ages 5 and 10, body mass index (BMI) at age 18, weight in 1989 and 2009, waist circumference, and height was obtained from the daughter. Polytomous logistic regression was used to predict BMI in early adulthood and adulthood, and body fatness in childhood. Linear regression was used to predict waist circumference in adulthood.

Results

In utero exposure to prenatal vitamins was not associated with body fatness, either in childhood or adulthood. Women whose mothers took prenatal vitamins during pregnancy had a covariate-adjusted odds ratio of being obese in adulthood of 0.99 (95% CI 0.92 – 1.05, P-value = 0.68) compared to women whose mothers did not take prenatal vitamins. Women whose mothers took prenatal vitamins during pregnancy had a covariate-adjusted odds ratio of having the largest body shape at age 5 of 1.02 (95% CI 0.90 – 1.15, P-value = 0.78). In additional analyses, in utero exposure to prenatal vitamins was also unrelated to adult abdominal adiposity.

Conclusions

Exposure to prenatal vitamins was not associated with body fatness either in childhood or in adulthood.

Parental smoking during pregnancy and risk of overweight and obesity in the daughter

Objective

Emerging evidence suggests that prenatal exposures may affect long-term health outcomes. In utero exposure to smoking is associated with an increased risk of overweight and obesity in children and adolescents. However, few studies have examined how prenatal exposure to parental smoking influences risk of obesity in adulthood and whether these associations are independent of childhood and adolescent adiposity. The aim of the current study was to investigate whether prenatal exposure to parental smoking influences body size in adulthood and whether any association may be mediated by childhood and adolescent body size.

Methods

We investigated the association between parental smoking during pregnancy and risk of overweight and obesity in adulthood and at age 18, and adiposity during childhood among 35,370 participants in the Nurses’ Health Study II. Data on smoking during pregnancy and socioeconomic variables were provided by the mothers, and anthropometric data and adult risk factors were reported by participants.

Results

After adjustment for socioeconomic and behavioral variables, maternal smoking during pregnancy was associated with adiposity at ages 5–10, age 18, and during adulthood. For age 18 overweight the ORs (95% CIs) for 1–14, 15–24, and 25+cigarettes/day were 1.13 (1.18–1.50), 1.40 (1.20–1.64), and 1.15 (0.79–1.69) and for obesity were 1.41 (1.14–1.75), 1.69 (1.31–2.18), and 2.36 (1.44–3.86). The corresponding ORs (95% CIs) for obesity in adulthood were 1.26 (1.16–1.37), 1.46 (1.30–1.63), and 1.43 (1.10–1.86). Risk of adiposity was not increased among daughters whose mothers stopped smoking during the first trimester (OR [95% CI] for overweight (1.03 [95% CI 0.90–1.17] and obesity (1.12 [95% CI 0.97–1.30]). Women whose fathers smoked during pregnancy were also at increased risk of overweight and obesity in adulthood with covariate-adjusted ORs (95% CIs) for obesity of 1.19 (1.11–1.29) for 1–14 cigarettes/day, 1.27 (1.18–1.37) for 15–24 cigarettes/day, and 1.40 (1.27–1.54) for 25+ cigarettes/day compared to fathers who did not smoke (p_trend<0.0001). Paternal smoking during pregnancy was also associated with an increased risk of obesity at age 18 among those whose fathers smoked 15 or more cigarettes/day but was not associated with childhood body size.

Conclusions

Maternal smoking during pregnancy was associated in a dose-response manner with overweight and obesity in the daughter through adolescence and adult life. Smoking cessation during the first trimester appears to mitigate this excess risk.

Paternal smoking was also associated with risk of overweight and obesity of the adult daughter and this association persisted after adjustment for maternal smoking.

Methylation levels at imprinting control regions are not altered with ovulation induction or in vitro fertilization in a birth cohort

STUDY QUESTION

Do fertility treatments, including ovulation induction (OI), alter epigenetic mechanisms such as DNA methylation at imprinted loci?

SUMMARY ANSWER

We observed small but statistically significant differences in certain imprinting control regions (ICRs) based on the method of conception, however, these small changes in methylation did not correlate to the overall transcriptional levels of the genes adjacent to the ICRs (such as KCNQ1 and SNRPN).

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

Assisted reproductive technology (ART) has been associated with an increase in the risk of rare childhood disorders caused by loss of imprinting (LOI). This study provides novel epigenetic analyses on infants conceived by OI and examines how methylation levels correlate with gene expression.

DESIGN

Data and biospecimens used in this study were from 147 participants of the Epigenetic Birth Cohort comprising 1941 mother-child dyads recruited between June 2007 and June 2009 at the Department of Obstetrics, Gynecology and Reproductive Biology at Brigham and Women's Hospital (BWH) in Boston, MA, USA. Wilcoxon rank-sum tests were used to examine the differences in median percent methylation at each differentially methylated region (DMR) between the spontaneous conception control group and the fertility treatment groups (OI and IVF).

PARTICIPANTS AND SETTING

For each woman who reported IVF we selected a woman who conceived spontaneously matched on age (± 2 years). To increase efficiency, we matched the same controls from the spontaneously conceived group to participants who reported OI. If an appropriate control was not identified that had been previously matched to an IVF participant, a new control was selected. The final analytic sample consisted of 61 spontaneous, 59 IVF and 27 OI conceptions.

MAIN RESULTS AND THE ROLE OF CHANCE

No functionally relevant differences in methylation levels were observed across five (out of six) imprinted DMRs in either the placenta or cord blood of infants conceived with OI or IVF compared with infants conceived spontaneously. While KCNQ1, SNRPN and H19 DMRs demonstrated small but statistically significant differences in methylation based on the method of conception, expression levels of the genes related to these control regions only correlated with the methylation levels of H19.

BIAS, CONFOUNDING AND OTHER REASONS FOR CAUTION

Limitations of our study include the limited sample size, lack of information on OI medication used and culture medium for the IVF procedures and underlying reasons for infertility among OI and IVF patients. We did not perform allele-specific expression analyses and therefore cannot make any inferences about LOI.

GENERALIZABILITY TO OTHER POPULATIONS

These results are likely to be generalizable to non-Hispanic white individuals in populations with similar ART and fertility treatments.

DNA methylation of stress-related genes and LINE-1 repetitive elements across the healthy human placenta

OBJECTIVES

DNA methylation is known to play a critical role in regulating development of placental morphology and physiology. The methylation of genes mediated by glucocorticoid hormones may be particularly vulnerable to intrauterine stress in the placenta. However little is known about DNA methylation of stress-related genes within a healthy placenta, and particularly whether methylation occurs uniformly across different regions of the placenta, which is a critical question for researchers seeking to analyze methylation patterns. We examined DNA methylation across four regions of the placenta to evaluate methylation levels of stress-related genes within a healthy placenta, and to evaluate whether methylation patterns vary by sampling location.

STUDY DESIGN

We evaluated levels of DNA methylation of three stress-related genes: NR3C1, BDNF, and 11B-HSD2 and of the repetitive element, LINE-1, in four different sample locations of 20 healthy placentas.

MAIN OUTCOME MEASURES

Pyrosequencing was used to quantify levels of methylation at CpG sites within the promoter regions of each of the three stress-related genes, and global methylation of LINE-1.

RESULTS

Very low levels of methylation were found across all three stress-related genes; no gene showed a median methylation level greater than 4.20% across placental regions. Variation in methylation between placental regions for stress-related genes and for LINE-1 was minimal.

CONCLUSIONS

Our data suggest that these frequently studied stress-related genes have low levels of methylation in healthy placenta tissue. Minimal variation between sites suggests that sampling location does not affect DNA methylation analyses of these genes or of LINE-1 repetitive elements.

The Early Determinants of Adult Health Study

This issue of the Journal features collaborative follow-up studies of two unique pregnancy cohorts recruited during 1959-1966 in the United States. Here we introduce the Early Determinants of Adult Health (EDAH) study. EDAH was designed to compare health outcomes in midlife (age 40s) for same-sex siblings discordant on birthweight for gestational age. A sufficient sample of discordant siblings could only be obtained by combining these two cohorts in a single follow-up study. All of the subsequent six papers are either based upon the EDAH sample or are related to it in various ways. For example, three papers report results from studies that significantly extended the 'core' EDAH sample to address specific questions. We first present the overall design of and rationale for the EDAH study. Then we offer a synopsis of past work with the two cohorts to provide a context for both EDAH and the related studies. Next, we describe the recruitment and assessment procedures for the core EDAH sample. This includes the process of sampling and recruitment of potential participants; a comparison of those who were assessed and not assessed based on archived data; the methods used in the adult follow-up assessment; and the characteristics at follow-up of those who were assessed. We provide online supplementary tables with much further detail. Finally, we note further work in progress on EDAH and related studies, and draw attention to the broader implications of this endeavor.

Maternal-recalled gestational weight gain, pre-pregnancy body mass index, and obesity in the daughter

Objective

Emerging evidence suggests that exposures during fetal life affect adult metabolism. We assessed the relation between recalled maternal pre-pregnancy body mass, gestational weight gain (GWG), and adiposity in the daughter.

Design

Retrospective cohort study among mother-nurse daughter dyads in the Nurses’ Health Study II and the Nurses’ Mothers’ Cohort. Mothers of participants completed questionnaires regarding their nurse-daughter in 2001.

Participants

26,506 mother-nurse daughter dyads born between 1946 and 1964.

Main outcome measures

Body mass index of the nurse-daughter at age 18 and in 2001.

Results

At age 18, 561 (2.1%) daughters were obese (BMI greater than 30), and in 2001, 5,442 (22.0%) were obese. Adjusting for covariates, women whose mothers had a recalled pre-pregnancy BMI of 29 had a 6.1-fold increased risk of obesity at age 18 and a 3.4-fold risk of obesity in 2001, compared with women whose mothers had a pre-pregnancy BMI of 21. We found a U-shaped association between recalled GWG and offspring obesity. Compared with a maternal weight gain of 15–19 lb, GWG <10 lbs was associated with a significant increase in obesity risk at age 18 (odds ratio[OR] 1.54, 95% confidence interval[CI] 1.02–2.34) and in 2001 (OR 1.27, 95%CI 1.05–1.53). High weight gain (40+ lbs) was also associated with obesity risk at age 18 (OR 1.81, 95%CI 1.22–2.69) and in 2001 (OR 1.74, 95%CI 1.48–2.04). These associations were stronger among mothers who were overweight prior to pregnancy (p for interaction = 0.03), and they persisted with adjustment for birth weight.

Conclusion

A high recalled pre-pregnancy BMI and extremes of recalled GWG are associated with an increased risk of adolescent and adult obesity in offspring, particularly when the mother is overweight. Pre-pregnancy weight and GWG may be modifiable fetal origins of overweight and obesity in women.

Inverse association of farm milk consumption with asthma and allergy in rural and suburban populations across Europe

BACKGROUND

Dietary interventions as a means for atopy prevention attract great interest. Some studies in rural environments claimed an inverse association between consumption of farm-produced dairy products and the prevalence of allergic diseases, but current evidence is controversial.

OBJECTIVE

To investigate whether consumption of farm-produced products is associated with a lower prevalence of asthma and allergy when compared with shop-purchased products.

METHODS

Cross sectional multi-centre study (PARSIFAL) including 14,893 children aged 5-13 years from five European countries (2823 from farm families and 4606 attending Steiner Schools as well as 5440 farm reference and 2024 Steiner reference children). A detailed questionnaire including a dietary component was completed and allergen-specific IgE was measured in serum.

RESULTS

Farm milk consumption ever in life showed a statistically significant inverse association with asthma: covariate adjusted odds ratio (aOR) 0.74 [95% confidence interval (CI) 0.61-0.88], rhinoconjunctivitis: aOR 0.56 (0.43-0.73) and sensitization to pollen and the food mix fx5 (cut-off level of >or=3.5 kU/L): aOR 0.67 (0.47-0.96) and aOR 0.42 (0.19-0.92), respectively, and sensitization to horse dander: aOR 0.50 (95% CI 0.28-0.87). The associations were observed in all four subpopulations and independent of farm-related co-exposures. Other farm-produced products were not independently related to any allergy-related health outcome.

CONCLUSION

Our results indicate that consumption of farm milk may offer protection against asthma and allergy. A deepened understanding of the relevant protective components of farm milk and a better insight into the biological mechanisms underlying this association are warranted as a basis for the development of a safe product for prevention.

A longitudinal study of infant feeding and obesity throughout life course

BACKGROUND

The Centers for Disease Control and Prevention and the US Department of Health and Human Services promote breastfeeding as a strategy for reducing childhood overweight. We evaluated the relation between infant feeding and the development of overweight and obesity throughout life course.

METHODS

We investigated the association between infant feeding and obesity among 35,526 participants in the Nurses' Health Study II who were followed prospectively from 1989 to 2001. Mothers of participants provided information by mailed questionnaires on the duration of breast- and bottle-feeding, as well as the type of milk or milk substitute in the bottle. Information on body shape at ages 5 and 10, weight at age 18, current weight between 1989 and 2001, and height was reported by the participants.

RESULTS

The duration of breastfeeding, including exclusive breastfeeding, was not related to being overweight (25< or = body mass index (BMI) <30 kg/m(2)) or obese (BMI> or =30 kg/m(2)) during adult life. Women who were exclusively breastfed for more than 6 months had a risk of 0.94 (95% confidence interval (CI) 0.83-1.07) of becoming obese as adults compared with women who were not breastfed. Exclusive breastfeeding for more than 6 months was associated with leaner body shape at age 5 (odds ratio (OR)=0.81; 95% CI 0.65-1.01 for the highest vs the lowest category of body shape) compared to women who were not breastfed or breastfed for less than 1 week, but this association did not persist during adolescence or adulthood.

CONCLUSIONS

We did not find that having been breastfed was associated with women's likelihood of becoming overweight or obese throughout life course. Although breastfeeding promotes the health of mother and child, it is unlikely to play an important role in controlling the obesity epidemic.

Allergic diseases and atopic sensitization in children related to farming and anthroposophic lifestyle--the PARSIFAL study

BACKGROUND

The prevalence of allergic diseases has increased rapidly in recent decades, particularly in children. For adequate prevention it is important not only to identify risk factors, but also possible protective factors. The aim of this study was to compare the prevalence of allergic diseases and sensitization between farm children, children in anthroposophic families, and reference children, with the aim to identify factors that may protect against allergic disease.

METHODS

The study was of cross-sectional design and included 14,893 children, aged 5-13 years, from farm families, anthroposophic families (recruited from Steiner schools) and reference children in Austria, Germany, The Netherlands, Sweden and Switzerland. A detailed questionnaire was completed and allergen-specific IgE was measured in blood.

RESULTS

Growing up on a farm was found to have a protective effect against all outcomes studied, both self-reported, such as rhinoconjunctivitis, wheezing, atopic eczema and asthma and sensitization (allergen specific IgE > or = 0.35 kU/l). The adjusted odds ratio (OR) for current rhinoconjunctivitis symptoms was 0.50 (95% confidence interval (CI) 0.38-0.65) and for atopic sensitization 0.53 (95% CI 0.42-0.67) for the farm children compared to their references. The prevalence of allergic symptoms and sensitization was also lower among Steiner school children compared to reference children, but the difference was less pronounced and not as consistent between countries, adjusted OR for current rhinoconjunctivitis symptoms was 0.69 (95% CI 0.56-0.86) and for atopic sensitization 0.73 (95% CI 0.58-0.92).

CONCLUSIONS

This study indicates that growing up on a farm, and to a lesser extent leading an anthroposophic life style may confer protection from both sensitization and allergic diseases in childhood.

Correlated measurement error--implications for nutritional epidemiology

BACKGROUND

In nutritional epidemiology, it is common to fit models in which several dietary variables are included. However, with standard instruments for dietary assessment, not only are the intakes of many nutrients often highly correlated, but the errors in the estimation of the intake of different nutrients are also correlated. The effect of this error correlation on the results of observational studies has been little investigated. This paper describes the effect on multivariate regression coefficients of different levels of correlation, both between the variables themselves and between the errors of estimation of these variables.

METHODS

Using a simple model for the multivariate error structure, we examine the effect on the estimates of bivariate linear regression coefficients of (1) differential precision of measurement of the two independent variables, (2) differing levels of correlation between the true values of the two variables, and (3) differing levels of correlation between the errors of measurement of the two variables. As an example, the prediction of plasma vitamin C levels by dietary intake variables is considered, using data from the European Prospective Investigation of Cancer (EPIC) Norfolk study in which dietary intake was estimated using both a food frequency questionnaire (FFQ) and a 7-day diary (7DD). The dietary variables considered are vitamin C, fat, and energy, with different approaches taken to energy adjustment.

RESULTS

When the error correlation is zero, the estimates of the bivariate regression coefficients reflect the precision of measurement of the two variables and mutual confounding. The sum of the observed regression coefficients is biased towards the null as in univariate regression. When the error correlation is non-zero but below about 0.7, the effect is minor. However, as the error correlation increases beyond 0.8 the effect becomes large and highly dependent on the relative precision with which the two variables are measured. At the extreme, the bivariate estimates can become indefinitely large. In the example, the error correlation between fat and energy using the FFQ appears to be over 0.9, the corresponding value for the 7DD being approximately 0.85. The error correlation between vitamin C and fat, and vitamin C and energy, appears to be below 0.5 and smaller for the 7DD than for the FFQ. The impact of these error correlations on bivariate regression coefficients is large. The effect of energy adjustment differs widely between vitamin C and fat.

CONCLUSION

High levels of error correlation can have a large effect on bivariate regression estimates, varying widely depending on which two variables are considered. In particular, the effect of energy adjustment will vary widely. For vitamin C, the effect of energy adjustment appears negligible, whereas for fat the effect is large indicating that error correlation close to one can partially remove regression dilution due to measurement error. If, for fat intake, energy adjustment is performed by using energy density, the partial removal of regression dilution is achieved at the expense of substantial reduction in the true variance.

Fruit, vegetables, dietary fiber, and risk of colorectal cancer

BACKGROUND

Several recent large prospective cohort studies have failed to demonstrate the presumed protective effect of fruit, vegetable, and dietary fiber consumption on colorectal cancer risk. To further explore this issue, we have examined these associations in a population that consumes relatively low amounts of fruit and vegetables and high amounts of cereals.

METHODS

We examined data obtained from a food-frequency questionnaire used in a population-based prospective mammography screening study of women in central Sweden. Women with colorectal cancer diagnosed through December 31, 1998, were identified by linkage to regional cancer registries. Cox proportional hazards models were used to estimate relative risks. All statistical tests were two-sided.

RESULTS

During an average 9.6 years of follow-up of 61 463 women, we observed 460 incident cases of colorectal cancer (291 colon cancers, 159 rectal cancers, and 10 cancers at both sites). In the entire study population, total fruit and vegetable consumption was inversely associated with colorectal cancer risk. Subanalyses showed that this association was due largely to fruit consumption. The association was stronger, however, and the dose-response effect was more evident among individuals who consumed the lowest amounts of fruit and vegetables. Individuals who consumed less than 1.5 servings of fruit and vegetables per day had a relative risk for developing colorectal cancer of 1.65 (95% confidence interval = 1.23 to 2.20; P(trend) =.001) compared with individuals who consumed more than 2.5 servings. We observed no association between colorectal cancer risk and the consumption of cereal fiber, even at amounts substantially greater than previously examined, or of non-cereal fiber.

CONCLUSIONS

Individuals who consume very low amounts of fruit and vegetables have the greatest risk of colorectal cancer. Relatively high consumption of cereal fiber does not appear to lower the risk of colorectal cancer.

Dietary antioxidant vitamins, retinol, and breast cancer incidence in a cohort of Swedish women

Dietary antioxidant vitamins and retinol have been proposed to be protective against breast cancer on the basis of their ability to reduce oxidative DNA damage and their role in cell differentiation. Epidemiologic studies have not been convincing in supporting this hypothesis, but women with high exposure to free radicals and oxidative processes have not been specifically considered. We explored these issues in the Swedish Mammography Screening Cohort, a large population-based prospective cohort study in Sweden that comprised 59,036 women, 40-76 years of age, who were free of cancer at baseline and who had answered a validated 67-item food frequency questionnaire. During 508,267 person-years of follow-up, 1,271 cases of invasive breast cancer were diagnosed. Cox proportional hazards models were used to obtain hazard ratios (HRs) and 95% confidence intervals (CIs). There was no overall association between intake of ascorbic acid, beta-carotene, retinol or vitamin E and breast cancer incidence. High intake of ascorbic acid was inversely related to breast cancer incidence among overweight women (HR=0.61; 95% CI 0.45-0.82, for highest quintile of intake among women with body mass index>25 kg/m(2)) and women with high consumption of linoleic acid (HR=0.72; 95% CI 0.52-1.02, for highest quintile of ascorbic acid intake and average consumption of more than 6 grams of linoleic acid per day). Among women with a body mass index of 25 or below, the hazard ratio for breast cancer incidence was 1.27 (95% CI 0.99-1.63), comparing the highest to the lowest quintile of ascorbic acid intake. Consumption of foods high in ascorbic acid may convey protection from breast cancer among women who are overweight and/or have a high intake of linoleic acid.

Being breastfed in infancy and breast cancer incidence in adult life: results from the two nurses' health studies

Events during perinatal and early life may influence the incidence of breast cancer in adult life, and some case-control studies suggest that having been breastfed may reduce breast cancer risk. The authors studied this association among premenopausal and postmenopausal women by using data from the two Nurses' Health Studies, the Nurses' Health Study (using data from 1992 to 1996) and the Nurses' Health Study II (using data from 1991 to 1997). A history of being breastfed was self-reported by the study participants. During a total of 695,655 person-years, 1,073 cases of invasive breast cancer were diagnosed. The authors did not observe any important overall association between having been breastfed and the development of breast cancer later in life among premenopausal women (covariate-adjusted relative risk = 0.97, 95% confidence interval (CI): 0.78, 1.20) or postmenopausal women (covariate-adjusted relative risk = 1.12, 95% CI: 0.92, 1.37). No significant trend was observed with increasing duration of breastfeeding. The authors also used data on breastfeeding retrospectively collected from 2,103 mothers of participants of the two Nurses' Health Studies. With the mothers' reports, the covariate-adjusted odds ratio of breast cancer was 1.11 (95% CI: 0.88, 1.39) for women who were breastfed compared with those who were not. Data from these two large cohorts do not support the hypothesis that being breastfed confers protection against subsequent breast cancer.

Prospective study of fruit and vegetable consumption and incidence of colon and rectal cancers

BACKGROUND

Frequent consumption of fruit and vegetables has been associated with a reduced risk of colorectal cancer in many observational studies.

METHODS

We prospectively investigated the association between fruit and vegetable consumption and the incidence of colon and rectal cancers in two large cohorts: the Nurses' Health Study (88 764 women) and the Health Professionals' Follow-up Study (47 325 men). Diet was assessed and cumulatively updated in 1980, 1984, 1986, and 1990 among women and in 1986 and 1990 among men. The incidence of cancer of the colon and rectum was ascertained up to June or January of 1996, respectively. Relative risk (RR) estimates were calculated with the use of pooled logistic regression models accounting for various potential confounders. All statistical tests were two-sided.

RESULTS

With a follow-up including 1 743 645 person-years and 937 cases of colon cancer, we found little association of colon cancer incidence with fruit and vegetable consumption. For women and men combined, a difference in fruit and vegetable consumption of one additional serving per day was associated with a covariate-adjusted RR of 1.02 (95% confidence interval [CI] = 0.98-1.05). A difference in vegetable consumption of one additional serving per day was associated with an RR of 1.03 (95% CI = 0.97-1.09). Similar results were obtained for women and men considered separately. A difference in fruit consumption of one additional serving per day was associated with a covariate-adjusted RR for colon cancer of 0.96 (95% CI = 0.89-1.03) among women and 1. 08 (95% CI = 1.00-1.16) among men. For rectal cancer (total, 244 cases), a difference in fruit and vegetable consumption of one additional serving per day was associated with an RR of 1.02 (95% CI = 0.95-1.09) in men and women combined. None of these associations was modified by vitamin supplement use or smoking habits.

CONCLUSIONS

Although fruits and vegetables may confer protection against some chronic diseases, their frequent consumption does not appear to confer protection from colon or rectal cancer.

alpha-fetoprotein levels in maternal serum during pregnancy and maternal breast cancer incidence

BACKGROUND

A full-term pregnancy is associated with a reduced risk of breast cancer, but the underlying biologic mechanism has not been elucidated. During pregnancy, maternal serum levels of alpha-fetoprotein, an estradiol-binding protein, rise sharply. In culture, alpha-fetoprotein inhibits the growth of estrogen-sensitive cells, including estrogen-sensitive breast cancer cells. Thus, we investigated whether a high level of alpha-fetoprotein in maternal serum during pregnancy is associated with a reduced risk of breast cancer.

METHODS

From a population-based cohort of 42057 pregnant women in Denmark, enrolled in an alpha-fetoprotein-screening program from 1978 through 1996, we obtained a complete reproductive history, vital status, and a possible diagnosis of breast cancer (in 117 women) to the end of follow-up on September 1, 1998.

RESULTS

During pregnancy, women with an alpha-fetoprotein level greater than or equal to the median value had a 41% lower risk of breast cancer than women with an alpha-fetoprotein level below the median value (relative risk [RR] = 0.59; 95% confidence interval [CI] = 0.41-0. 85). RRs for breast cancer by mother's age at childbirth were as follows: 29 years or younger, RR = 0.21 (95% CI = 0.08-0.56); 30-34 years, RR = 0.61 (95% CI = 0.32-1.14); 35-37 years, RR = 0.96 (95% CI = 0.49-1.89); and 38 years or older, RR = 0.71 (95% CI = 0.29-1. 75) (P for trend =.02). Further analyses suggested that high levels of alpha-fetoprotein were associated with a reduced incidence of aggressive disease. The most striking finding was that women with high levels of serum alpha-fetoprotein, compared with women with low levels of serum alpha-fetoprotein, showed a particularly reduced incidence of large tumors (>2 cm; RR = 0.24 [95% CI = 0.11-0.50]).

CONCLUSION

A high level of alpha-fetoprotein in maternal serum during any pregnancy is associated with a low overall incidence of breast cancer and, in particular, with a low incidence of advanced breast cancer at diagnosis. This association appears particularly strong for a pregnancy occurring at a young age.

Reproducibility and validity of maternal recall of pregnancy-related events

We assessed the reproducibility and validity of a questionnaire that asks mothers to recall pregnancy-related events from thirty or more years ago. Among 146 women who completed the questionnaire twice, responses were highly reproducible for pre-pregnancy height and weight (r = 0.95), pregnancy complications (r = 0.74), substance use (r = 0.80), preterm delivery (r = 0.82), birthweight (r = 0.94), and breastfeeding (r = 0.89). Among 154 women whose questionnaire responses were compared to data collected during their pregnancies, recall was highly accurate for height (r = 0.90), pre-pregnancy weight (r = 0.86), birthweight (r = 0.91), and smoking (sensitivity = 0.86, specificity = 0.94). These findings suggest that long-term maternal recall is both reproducible and accurate for many factors related to pregnancy and delivery.

Presenting statistical uncertainty in trends and dose-response relations

When one estimates the effects of a polytomous exposure, it is common practice to express all effects relative to a baseline or reference level. Certain authors have challenged this practice and proposed alternatives, which we review here. One alternative, the "floating absolute risk" method, can supply useful statistics and trend graphs, but it does not yield valid confidence intervals for relative risks. All categorical methods have further shortcomings when the exposure is continuous, however. These shortcomings can be addressed by plotting or tabulating confidence limits for points on a flexible curve fitted to the uncategorized data.

Problems assessing nonserious adverse drug reactions: antidepressant drug therapy and sexual dysfunction

Adverse drug reactions (ADRs) pose a challenge to prescribing physicians, especially when they considerably compromise the patient's quality of life and thus affect compliance. Adverse events that do not pose a severe threat to the patient's health and are therefore considered nonserious are understudied in pharmacotherapy. Such events are seldom systematically assessed, and frequency figures are usually not reliable. An example of a nonserious ADR is sexual dysfunction associated with antidepressant therapy. This is a problem of considerable importance to patients, yet its incidence is underestimated in product information. Incidence data on sexual dysfunction would assist physicians' decision making and improve care. It is suggested that premarketing and postmarketing clinical trials and pharmacoepidemiologic studies include systematic assessment of selected and important nonserious adverse effects to provide more accurate estimates of their true incidence; and that product labeling be regularly updated to reflect postmarketing experience.

Prospective study of adult onset diabetes mellitus (type 2) and risk of colorectal cancer in women

BACKGROUND

The remarkable similarity of lifestyle and environmental risk factors for type 2 (non-insulin-dependent) diabetes mellitus and colon cancer has led to the hypothesis that diabetes may increase the risk of this cancer. We prospectively examined the relationship between diabetes and risk of colorectal cancer in a cohort of 118403 women aged 30 through 55 years who were without previously diagnosed cancer at baseline in 1976.

METHODS

The women, who were enrolled in the Nurses' Health Study, were assessed for history of diabetes at baseline and during follow-up by use of biennial questionnaires. Self-reported diabetes was validated by information obtained from a supplemental questionnaire on symptoms and treatment and was confirmed by medical record review in a sample of the participants. Incident cases of colorectal cancer were ascertained through medical record review. All reported P values are two-sided.

RESULTS

During 18 years of follow-up (201061 person-years), we documented 892 new cases of colorectal cancer. After adjustment for age, body mass index (weight in kg/height in m2), physical activity, and other covariates, relative risks (RRs) were 1.43 (95% confidence interval [CI] = 1.10-1.87; P = .009) for colorectal cancer, 1.49 (95% CI = 1.09-2.06; P = .01) for colon cancer, 1.11 (95% CI = 0.56-2.21; P = .76) for rectal cancer, 1.56 (95% CI = 1.07-2.28; P = .02) for advanced colorectal cancer, and 2.39 (95% CI = 1.46-3.92; P = .0005) for fatal colorectal cancer.

CONCLUSION

Our data provide support for the hypothesis that diabetes is associated with an increased risk of colorectal cancer in women.

Calcium channel blockers, cancer incidence, and cancer mortality in a cohort of U.S. women: the nurses' health study

BACKGROUND

Some studies have suggested that the use of calcium channel blockers may increase the risk of cancer. A possible association of the use of calcium channel blockers with cancer incidence and cancer mortality was addressed using data from the Nurses' Health Study.

METHODS

In this study, a total of 18,635 female nurses reported regularly taking at least 1 of 4 cardiovascular medications in 1988: diuretics, beta-blockers, calcium channel blockers, and/or angiotensin-converting enzyme (ACE) inhibitors. Cancer incidence and cancer deaths were ascertained until 1994.

RESULTS

During 6 years of follow-up, 852 women were newly diagnosed with cancer and 335 women died of cancer. Women who reported the use of calcium channel blockers had no increased risk of newly diagnosed cancer compared with those taking other cardiovascular drugs (relative risk=1.02; 95% CI 0.83-1.26). The relative risk of dying from cancer associated with the self-reported use of calcium channel blockers was 1.25 (95% CI 0.91-1.72). Relative risks were adjusted for the following self-reported factors: age; weight; height; cholesterol level; systolic and diastolic blood pressure; smoking; alcohol intake; physical activity; menopausal status; postmenopausal hormone use; aspirin use; and history of diabetes, cancer, stroke, myocardial infarction, coronary artery bypass graft or percutaneous transluminal coronary angioplasty, angina, and hypertension. Regarding site specific cancer incidence and mortality, only lung cancer incidence was somewhat increased (RR=1.61; 95% CI 0.88-2.96).

CONCLUSIONS

These data suggest no important increase in overall cancer incidence or cancer mortality related to the self-reported use of calcium channel blockers.

Prospective study of calcium channel blocker use, cardiovascular disease, and total mortality among hypertensive women: the Nurses' Health Study

BACKGROUND

In several observational studies, patients prescribed calcium channel blockers had higher risks of cardiovascular diseases and mortality than those prescribed other antihypertensive medications. We explored these associations in the Nurses' Health Study.

METHODS AND RESULTS

A total of 14 617 women who reported hypertension and regular use of diuretics, beta-blockers, calcium channel blockers, ACE inhibitors, or a combination in 1988 were included in the analyses. Cardiovascular events and deaths were ascertained through May 1, 1994. We documented 234 cases of myocardial infarction. Calcium channel blocker monodrug users had an age-adjusted relative risk (RR) of myocardial infarction of 2.36 (95% CI, 1.43 to 3.91) compared with those prescribed thiazide diuretics. Women prescribed calcium channel blockers had a higher prevalence of ischemic heart disease. After adjustment for these and other coronary risk factors, the RR was 1.64 (95% CI, 0.97 to 2.77). Comparing the use of any calcium channel blocker (monodrug and multidrug users) with that of any other antihypertensive agent, the adjusted RR was 1.42 (95% CI, 1.01 to 2.01). An association between calcium channel blocker use and myocardial infarction was apparent among women who had ever smoked cigarettes (covariate-adjusted RR, 1.81; 95% CI, 1.20 to 2.72) but not among never-smokers (RR, 0.94; 95% CI, 0.48 to 1.84).

CONCLUSIONS

In analyses adjusted only for age, we found a significant elevation in RR of total myocardial infarction among women who used calcium channel blockers compared with those who did not. After adjustment for comorbidity and other covariates, the RR was reduced. Whether the remaining observed elevated risk is real, or a result of residual confounding by indication, or chance, or a combination of the above cannot be evaluated with certainty on the basis of these observational data.

Does body mass index adequately capture the relation of body composition and body size to health outcomes?

Body mass index (BMI) has become the most commonly used index of body composition in epidemiologic research. It has displaced weight, height, and other measures of body composition. In this paper, the authors show that use of BMI alone does not always capture adequately the joint relation of body composition and body size to health outcomes, and that such use often represents implausible restrictions on the relation. Use of body mass index and height or weight and height will often be needed to describe this relation and to control confounding by these variables.

Birthweight as a risk factor for breast cancer

BACKGROUND

The mammary gland is largely undifferentiated before birth and may be particularly susceptible to intrauterine influences that could increase the risk of cancer through acceleration of cell proliferation or other pregnancy-related processes. Studies of migrant populations, animal data, and limited epidemiological evidence suggest that breast cancer may originate in utero. In a nested case-control study we assessed whether birthweight and other perinatal factors are associated with risk of breast cancer.

METHODS

This case-control study was nested within the cohorts of the two Nurses' Health Studies. We used self-administered questionnaires to obtain information from the mothers of 582 nurses with invasive breast cancer and the mothers of 1569 nurses who did not have breast cancer (controls). Information on risk factors for breast cancer during adulthood were obtained from the nurses; multiple logistic regression analysis adjusted for these risk factors.

FINDINGS

Birthweight was a significant predictor of breast-cancer risk. With women who weighed 4000 g or more at birth as the reference category, the adjusted odds ratios for breast cancer were 0.86 (95% CI 0.59-1.25) for birthweights of 3500-3999 g, 0.68 (0.48-0.97) for birthweights of 3000-3499 g, 0.66 (0.45-0.98) for birthweights of 2500-2999 g, and 0.55 (0.33-0.93) for birthweights below 2500 g (p for trend 0.004). Prematurity was not significantly associated with risk of breast cancer.

INTERPRETATION

Birthweight is significantly associated with breast-cancer risk, which suggests that intrauterine factors or processes affect the risk of breast cancer in the offspring. High concentrations of pregnancy oestrogens may have an important role in breast carcinogenesis, but other pregnancy hormones or intrauterine factors may also be involved.

Does induced or spontaneous abortion affect the risk of breast cancer?

The influence of induced or spontaneous abortion on breast cancer risk has been the subject of numerous epidemiologic studies over the past decades and has recently received heightened attention. Here, we review the evidence to understand better the apparent inconsistencies among studies. We considered possible biases in data collection, presentation, and analysis that could create spurious associations or obscure real relations. A particularly important issue is the sensitive nature of abortion, which is a pervasive problem that could affect the validity of many studies. Also, an incomplete pregnancy deprives the woman of a potentially protective full-term pregnancy and therefore may appear harmful when compared with the experience of a woman who did carry to term. The dual effect of parity on breast cancer risk-short-term risk increase and long-term protection-adds another dimension of complexity to the interpretation of abortion studies. Long-term influences of abortion may have been insufficiently captured in some studies, as follow-up time was too short. Studies to date are inadequate to infer with confidence the relation between induced or spontaneous abortion and breast cancer risk, but it appears that any such relation is likely to be small or nonexistent.

Prospective assessment of breastfeeding and breast cancer incidence among 89,887 women

BACKGROUND

The relation between breastfeeding and breast cancer risk has been examined in many studies; some have reported no association, and others a reduced risk, particularly among premenopausal women. In the only prospective cohort study, no association was found. We have assessed prospectively the association between breastfeeding and incidence of breast cancer among 89,887 women in the US Nurses' Health Study.

METHODS

In 1986, participants were asked about the number of months they breastfed for all their children combined. Parous women with no history of cancer were included in this analysis. During 6 years of follow-up (513,015 person-years), 1,459 invasive breast cancer cases were diagnosed.

FINDINGS

Relative to women who had never breastfed, no significant overall association was found--after adjusting for established risk factors for breast cancer--between a history of having breastfed and subsequent development of breast cancer (relative risk [RR] 0.93, 95% CI 0.83 -1.03). No inverse trend was observed with duration of breastfeeding; women who breastfed for 2 years of longer had a RR of 1.11 (0.90-1.38). Among women who had given birth only once, women who had breastfed their child experienced a lower incidence of breast cancer (RR 0.68, 0.46-1.00). Among premenopausal women, who tended to be near menopause due to the age structure of the cohort, the RR of breast cancer for those who had lactated was 1.16 (0.89-1.50). Premenopausal women who had lactated for 1 year or more had a RR of 1.10 (0.78-1.57).

INTERPRETATION

These data suggest that there is no important overall association between breast-feeding and the occurrence of breast cancer.

Self-reported birthweight and history of having been breastfed among younger women: an assessment of validity

BACKGROUND

Recent evidence suggests potential associations between birthweight and infant feeding history and risk of a variety of health outcomes during adulthood. Because studies may rely on self-reported birthweight and infant feeding history, it is important to assess the validity of this information.

METHODS

The authors compared birthweights reported by a sample of 538 women, 27-44 years of age, participating in the Nurses' Healthy Study II (NHSII) cohort, with birthweights recalled by their mothers and with those from state birth records. In addition, we compared participants' self-reported history of having breastfed with their breastfeeding history reported by their mothers.

RESULTS

For birthweight, the correlation between reports by the cohort participants and by their mothers was high (Spearman r = 0.75). Compared with weights recorded on state birth records, correlations were 0.74 for reports by cohort participants and 0.85 for reports by their mothers. When comparing NHSII participants' self-report of ever having been breastfed with their mothers' report, sensitivity was 82% and specificity was 86%. For duration of breastfeeding, the Spearman correlation between mother and daughter reports was 0.74. In analyses stratified by four ethnic groups (African-American, Asian, Caucasian, and Hispanic) we observed substantial differences in distribution of birthweight and breastfeeding patterns; however, the degree of validity in reporting them was similar.

CONCLUSION

The validity of self-reported birthweight and breastfeeding history by these middle-aged women appears to be high.

The origins of Hodgkin's disease

Despite significant advances in treatment, the aetiology of Hodgkin's disease has remained elusive. While epidemiology has uncovered the likely infectious nature of the malignancy, neither the causative agent nor the cell of origin have been identified. The available epidemiological, histological and molecular biological evidence were reviewed and the following conclusions reached. Hodgkin's disease is probably an infectious, but not contagious disease, and is compounded by immunodeficiency. The suspected role of the Epstein-Barr virus (EBV) as causative agent has been substantially weakened, although a role as co-factor is likely. A prime candidate for the cell of origin seems the interdigitating reticulum cell (IRC). Reed-Sternberg cells found in patients with Hodgkin's disease may represent in vivo hybridomas of the IRC with B- and/or T-cells. As IRC is unlikely to be susceptible to EBV, a retrovirus may be the culprit. Hybridomas may be formed when retroviral antigens expressed by a macrophage cell attract reactive B- and T-cells and, instead of an immune reaction, fusion occurs. Further research is necessary in the search for the causative agent of Hodgkin's disease.

Abortion and the risk of breast cancer: a case-control study in Greece

We have examined the association between induced or spontaneous abortion and breast cancer risk in Greece. In a hospital-based case-control study in Athens, 820 patients with confirmed breast cancer were compared with 795 orthopedic patient controls and 753 healthy visitor controls, matched to cases by age and interviewer. Logistic regression was used to analyze the data, controlling for demographic, reproductive and nutritional variables. Odds ratio (OR) patterns were similar for the 2 control series, which were therefore combined to increase precision of the estimates. The risk for breast cancer was not increased for women who had a history of abortion, compared to nulliparous women with no history of abortion. Thus ORs and 95% confidence intervals were for nulliparous women with spontaneous abortion, 1.17 (0.64-2.13); for nulliparous women with induced abortion, 0.98 (0.56-1.73); for parous women with no abortion, 0.56 (0.31-1.01); for parous women with spontaneous abortion, 0.61 (0.33-1.14) and for parous women with induced abortion, 0.99 (0.56-1.74). When the analysis was restricted to parous women, using parous women with no history of abortion as the baseline, ORs and 95% confidence intervals were for induced abortion before first full-term pregnancy, 2.06 (1.45-2.90); for induced abortion after first full-term pregnancy, 1.59 (1.24-2.04) and for spontaneous abortion, 1.10 (0.82-1.40). Our findings suggest that an interrupted pregnancy does not impart the long-term protective effect of a full-term pregnancy attributable to terminal differentiation.

Does PTCA in acute myocardial infarction affect mortality and reinfarction rates? A quantitative overview (meta-analysis) of the randomized clinical trials

BACKGROUND

Percutaneous transluminal coronary angioplasty (PTCA) is often performed after acute myocardial infarction (AMI) either as an adjuvant to thrombolytic therapy or instead of thrombolysis. The effect of PTCA in AMI on mortality and reinfarction has remained unclear, with the available randomized trials indicating inconsistent results.

METHODS AND RESULTS

A systematic overview (meta-analysis) of the randomized trials was conducted to assess the effect of PTCA in AMI on mortality and reinfarction rates. Data from 7 trials in which primary PTCA was evaluated and 16 trials in which PTCA after thrombolysis was studied were included in this overview, comprising a total of 8496 patient. The trials represented different approaches to the timing of PTCA after AMI. The trials of PTCA after thrombolytic therapy were also categorized according to the different protocols with respect to the routine or elective character of PTCA in the invasive group. A reduction in short-term (6 week) mortality (odds ratio, 0.56; 95% CI, 0.33, 0.94) and in the combined outcome of short-term mortality and nonfatal reinfarction (odds ratio, 0.53; 95% CI, 0.35, 0.80) was observed in the trials comparing primary PTCA with thrombolytic therapy. In contrast, in trials in which an approach of thrombolysis and PTCA was compared with thrombolytic therapy alone, there was no important difference in early mortality, with an apparent reduction in mortality between 6 and 52 weeks. The lower mortality between 6 and 52 weeks among 6-week survivors seemed to be restricted to the subgroup of trials in which PTCA was used as a routine strategy (odds ratio, 0.58; 95% CI, 0.39, 0.87).

CONCLUSIONS

Although the analyses of the various categories of trials suggest that primary PTCA may be more beneficial than thrombolytic therapy in AMI, these data should be interpreted cautiously unless confirmed by larger studies. In contrast, the addition of various other strategies of PTCA to thrombolytic therapy does not convincingly indicate a clinically different outcome than if a more conservative strategy is followed, in which PTCA is used only if clinically indicated. Some specific strategies, however, such as rescue PTCA in high-risk patients with occluded arteries, may be of benefit.

Abortion and breast cancer risk in seven countries

Epidemiologic studies have been inconsistent in suggesting an association between abortion and breast cancer risk. Whether the protection provided by a full-term pregnancy also results from a short-term pregnancy or whether a prematurely terminated pregnancy could increase the risk of breast cancer is unclear. Data from a large, international collaborative study were used to evaluate the association between abortions, whether spontaneous or induced, and breast cancer risk. The data from seven countries included 3,958 breast cancer cases and 11,538 hospital controls with information on abortion history obtained through interviews. Compared with nulliparous women with no abortion (baseline), the odds ratios (OR) and 95 percent confidence intervals (CI) were: for nulliparous women with a history of prior abortion, 0.86 (CI = 0.68-1.08); for parous women with no history of abortion, 0.63 (CI = 0.57-0.69); for parous women with abortion before first birth, 0.82 (CI = 0.69-0.97); and, for parous women with abortion only after first birth, 0.70 (CI = 0.63-0.79). When restricting analysis to parous women, those with a history of abortion exhibited an elevated OR suggesting a 29 percent risk increase if the incomplete pregnancy occurred before first birth (CI = 1.16-1.36) and an 11 percent risk increase for abortion only after first birth (CI = 1.02-1.20) compared with women without such history. The associations observed were stronger among the youngest women. These results do not support a large overall association between abortion and breast cancer risk.