Vegetarian Nutrition

VN: Micronutrients in Pregnancy (2007)

Citation:

North K, Golding J. A maternal vegetarian diet in pregnancy is associated with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood. BJU Int. 2000 Jan;85(1):107-13.

PubMed ID: 10619956
 
Study Design:
Prospective Cohort Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To investigate the possible role of maternal nutrition in the origin of hypospadias. Spedifically, the hypothesis that exposure in pregnancy to phytoestrogens in the maternal diet may have a marked effect on the male offspring's reproductive system.
Inclusion Criteria:
  • Pregnant women with estimated delivery date between 1 April 1991 and 31 December 1992
  • Women must live in the three Bristol-based health districts of Avon
  • Women must complete questionnaire

Identifying Hypospadias:

  • Maternal reporting in postnatal questionnaires
  • Birth notifications
  • Records of examination by the neonatal pediatrician
  • Postmortem reports
Exclusion Criteria:
  • Failure to complete questionnaire
Description of Study Protocol:

Recruitment

  • Invitation of women with delivery date between 1 April 1991 and 31 December 1992 and living in three Bristol-based health care districts of Avon.
  • 51 hypospadias cases were identified.

Design

  • Subjects completed questionnaires at weeks 8, 18, and 32 as well as after birth at various ages of the child.  Questionnaires included number of previous pregnancies and outcome, age of beginning menstruation, consumption of oral contraceptives while pregnant, duration of attempting conception, duration of oral contraceptives, symptoms of ill-health, all medications taken, general lifestyle habits.

Statistical Analysis

The results were initially assessed using chi-squared analysis to detect any differences in the proportions of boys with hypospadias or not within the factors considered.  Unadjusted logistic regression was used to calculate odd ratios for significant factors, and multivariate logistic regression identified independent associations between factors and the risk of hypospadieas.

Data Collection Summary:

Timing of Measurements

Questionnaires completed at weeks 8, 18, and 32 of gestation and after birth at various ages of child.

Dependent Variables

  • Incidence of hypospadias in infant boys

Independent Variables

  • Type of diet consumed by birth mother during pregnancy
  • Iron supplementation during pregnancy

Control Variables

Description of Actual Data Sample:

Initial N: 7928 male births; 51 hypospadias cases

Ethnicity: Not reported

Location: Bristol, United Kingdom

 

Summary of Results:

Adjusted odds ration for independent factors associated with hypospadias (considering iron supplementation and vegetarianism separately and combining iron supplementation with vegetarianism or not)

Factor (%)

Odds Ration (95% CI)

P

Vegetarian during pregnancy

Yes (5.1)

No (94.9)

 

3.88 (1.69, 8.92)

1.00 Ref

 

 

0.0014

Taken iron tablets during pregnancy

Yes (43.0)

No (57.0)

 

1.81 (0.92, 3.55)

1.00 Ref

 

 

0.0848

Vegetarianism and iron supplementation

Omnivore, no iron (74.3)

Omnivore, with iron (20.5)

Vegetarian (5.2)

 

 

1.00 Ref

2.07 (1.00, 4.32)

4.99 (2.10, 11.88)

 

 

 

 

0.0009

Categorial factors studied in relation to hypospadias cases

Factor (%)

Cases, % (n)

×2 (P)

OR (95% CI)

Vegetarian during pregnancy (n=6296)

Yes (5.1)

No (77.2)

 

2.2 (7)

0.6 (37)

 

10.45 (0.001)

 

3.53 (1.56, 7.98)

1.00 Ref

Drank soy milk during pregnancy (n=6263)

Yes (1.4)

No (98.6)

 

2.2 (2)

0.6 (38)

 

3.61 (0.058)

 

3.67 (0.87, 15.44)

1.00 Ref

Ate pulses during pregnancy

Never (76.7)

Once in 2 weeks (14.3)

1-3 times/week (8)

4+ times/week (1.1)

 

0.6 (30)

 

0.4 (4)

0.8 (4)

4.5 (3)

 

 

 

 

 

16.13 (0.001)

 

1.00 Ref

 

0.72 (0.25, 2.04)

1.28 (0.45, 3.64)

7.56 (2.25, 25.42)

 At soy "meat" during pregnancy (n=6189)

Never (92.3)

Once in 2 weeks (5.1)

1+ times/week (2.7)

 

0.6 (36)

0.6 (2)

1.8 (3)

 

 

 

 

3.51 (0.173)

 

1.00 Ref

1.01 (0.24, 4.22)

2.95 (0.90, 9.68)

 Vegetarianism and iron supplementation (n=6071)

Omnivore, no iron (74.3)

Vegetarian, no iron (3.6)

Omnivore, with iron (20.5)

Vegetarian with iron (1.6)

 

 

0.5 (22)

2.3 (5)

 

1.1 (14)

2.1 (2)

 

 

 

 

 

 

 

 

16.59 (0.001)

 

 

1.00 Ref

4.81 (1.81, 12.84)

 

2.32 (1.19, 4.55)

4.30 (0.99, 18.54)

 Vegetarianism and iron supplementation (n=6071)

Omnivore, no iron (74.3)

Omnivore, with iron (20.5)

Vegetarian (5.2)

 

 

0.5 (22)

1.1 (14)

 

2.2 (7)

 

 

 

 

 

16.54 (<0.001)

 

 

1.00 Ref

2.32 (1.19, 4.55)

 

4.65 (1.97, 10.98)

Other Findings

Supplementing the diet with iron tablets in the first three months of pregnancy was associated with a significantly higher risk for hypospadias; 1% of mothers who took iron tablets had boys born with hypospadias, compared with 0.6% of those who did not (P = 0.041).

2.2% of mothers who ate a vegetarian diet during pregnancy gave birth to hypospadiacs compared with 0.6% of omnivores (P = 0.001)

The proportion of boys born with hypospadias was higher among mothers who drank soy milk (2.2%) and who regularly consumed soy products (1.8%), although not statistically significant.

Consumption of seeds of certain pod-bearing plants (dried peas, beans, lentils, and chickpeas) four or more times a week resulted in a significantly larger proportion of cases of hypospadias (4.5%, P=0.001).

Vegetarian mothers who did not take iron supplements were significantly more likely to give birth to boys with hypospadias, while omnivores who took iron were also more likely to bear boys with hypospadias.  However, the incidence of hypospadias in vegetarians who supplemented their diet with iron did not differ significantly from that in vegetarians that did not do so, suggesting that the effect of iron supplementation was only significant among omnivores.

Author Conclusion:

There was a higher proportion of boys with hypospadias born to mothers who were vegetarian during pregnancy. It is important to note that there is biological evidence that vegetarians have a greater exposure to phytoestrogens and thus a casual link is biologically feasible. 

However, "Present tables of food contents provide inadequate information about phytoestrogen content and hence it is not possible to make substantive comments on their effects on hypospadias."

Funding Source:
Government: Medical Research Council, Dept. of Health, Dept. of the Environment, MAFF (all UK)
Industry:
Nutricia, Nestle
Food Company:
Not-for-profit
0
Reviewer Comments:
Can race of infant and birth mother play a part in incidence of hypospadias?  Race of mothers  - especially of those who were vegetarian - who participated in this study was not mentioned.  The study failed to describe in detail the serving size of soy products consumed by vegetarians (number of times per week given but nothing more detailed).  Serum lab values of phytoestrogens or urinary levels of isoflavones during the different weeks of pregnancy would have been very beneficial in supporting the author's conclusions.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? No
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? No
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? No
  4.1. Were follow-up methods described and the same for all groups? No
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? No
  4.4. Were reasons for withdrawals similar across groups? No
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? No
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? No
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? No
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes