Vegetarian Nutrition

VN: Adolescence (2009)

Citation:

Gale C, Deary I, Schoon I, Batty GD. IQ in childhood and vegetarianism in adulthood: 1970 British cohort study. BMJ. 2007; 334: 245.

PubMed ID: 17175567
 
Study Design:
Cross-Sectional Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

The purpose of this study was to examine the effect of childhood IQ on the likelihood of being a vegetarian as an adult.

Inclusion Criteria:

Inclusion criteria included those who participated in the 1970 British Cohort study, a national birth cohort, who provided information on vegetarian status at age 30 and had data on IQ score at age 10 years.

Exclusion Criteria:

No exclusion criteria were specified.

Description of Study Protocol:

Recruitment    

Participants of the 1970 British Cohort study. 

Design             

This was a prospective cohort study that assessed mental ability at age 10 via IQ, and determined vegetarianism at age 30 via self-report.

Statistical Analysis                           

  • Analysis of covariance and xwere used to examine the characteristics of the participants.
  • Logistic regression was used to examine prospectively the relation between childhood IQ score and vegetarianism as an adult.
Data Collection Summary:

Timing of Measurements

  • At age 10 years, mental ability was assessed via IQ
  • At age 30 years, vegetarianism was determined via self-report.

Dependent Variables

  • Self-reported vegetarianism 
  • Type of diet, i.e. vegan, fish or chicken consumer vegetarians.

Independent Variables

 IQ of participants at age 10.

Control Variables

Sex, parental social class, current social class and academic or vocational qualifications.

Description of Actual Data Sample:
  • Initial N: 8,170 (4,222 females; 3,948 males); Comparison groups includes 7,804 non-vegetarians and 366 vegetarians, of which nine were vegans.
  • Attrition (final N): 8,170
  • Age: 30 years
  • Ethnicity: Primarily British
  • Other relevant demographics: Various social class and educational demographics
  • Location: Great Britain. 
Summary of Results:

 

Characteristics of Study Participants in Relation to Self-reported Vegetarianism at Age 30 Years (N=8,170)

Characteristics Total Number (%) of Non-vegetarians in Each Category Number (%) of Vegetarians in Each Category
Women 4,222 3,951 (50.6) 271 (74.0)
Men 3,948 3,853 (49.4) 95 (26.0)***

Parental social  class:a

     

   Professional 

2,244 2,119 (27.2) 125 (34.2)
   Skilled non-manual

752

719 (932) 33 (9.0)
   Semiskilled 3,081 2,945 (37.7) 136 (37.2)
   Unskilled 1,205 1,165 (14.9) 40 (10.9)
   Unknown 888 856 (11.0) 32 (8.7)*
Current social class:      
   Professional or managerial 2,968 2,798(35.8) 170 (46.5)
   Skilled non-manual 2,102 1,991 (25.5) 111 (30.3)
   Semiskilled 1,649 1,611 (20.6) 38 (10.4)
   Unskilled 1,274 1,235 (15.8) 39 (10.7)
   Unknown 177 169 (2.2) 8 (2.2)***
Academic or vocational qualifications:      
   No qualifications 695 685 (8.8) 10 (2.7)
   CSE equivalent NVQ 1 647 629 (8.1) 18 (4.9)
   O level or equivalent NVQ 2 2,320 2,246 (28.8) 74 (20.2)
   A level or equivalent NVQ 3 1,708 1,638 (21.0) 70 (19.1)
   Degree, diploma, or equivalent NVQ 4 2,494 2,331 (29.9) 163 (44.5)
   Higher degree or NVQ 5 306 275 (3.5) 31 (8.5)***
Annual gross earnings:b      
  <£11,440 1,491 1,424 (24.9) 70 (26.6)

   £11,441 to £16,600

1,496 1,432 (25.0) 64 (24.3)
   £16 601 to £23 000 1,518 1,451 (25.3) 67 (25.5)
   >£23 000 1,484 1,422 (24.8) 62 (23.6)

£1.00 (€1.48; $1.89).  NVQ=national vocational qualifications.

*P<0.05; ***P<0.001.

aDerived from mother's occupation if no father was present from whom to derive occupation.

bAvailable for 5,992 participants.

  • On average, vegetarians had a higher childhood IQ score than non-vegetarians. IQ scores of vegetarians compared with non-vegetarians was 106.1 (14.7) and 100.6 (15.2) for men and 104.0 (14.1) and 99.0 (14.7) for women (P< 0.001). 
  • After controlling for sex, the OR increased to 1.42 (1.28 to 1.59)
  • Although when adjusted for social class, both in childhood and at age 30, and academic or vocational qualifications, the OR was lower but still remained statistically significant
  • OR for being vegetarian at age 30 for one standard deviation increase in childhood IQ score was 1.38 (95% CI 1.24 to 1.53)

Odds Ratios (95% CI) for Being Vegetarian at Age 30 Years for a One Standard Deviation Increase in Childhood IQ Score in 8,170 Participants of the 1970 British Cohort Study

Adjustments Odds Ratio (95% CI)
Unadjusted 1.38 (1.24 to 1.53)
Sex 1.42 (1.28 to 1.59)
Parental social class 1.35 (1.21 to 1.51)
Current social class 1.29 (1.15 to 1.45)
Academic or vocational qualifications 1.16 (1.03 to 1.30)
All 1.20 (1.06 to 1.36)

  

Author Conclusion:

Participants of the 1970 British cohort study with higher intelligence test scores in childhood were more likely to report being a vegetarian at age 30 years.

Funding Source:
University/Hospital: Department of Child Health, Bristol University; Joint Centre for Longitudinal Research
Reviewer Comments:

The high statistical power related to this study's large size, and the representativeness of the sample group enables one to generalize the study findings for Britain's population born around the same time (1970).

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
  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
  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
  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) Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. 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
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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? 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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  3. Were study groups comparable? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) 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? 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? Yes
  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.) Yes
  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.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? 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? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  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%.) Yes
  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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  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? ???
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) 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.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? 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
  5.4. 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
  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. 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
  6.1. 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
  6.2. 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
  6.3. 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? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  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? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  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? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  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
  7.4. 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? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
  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. 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
  8.1. 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
  8.2. 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
  8.3. 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
  8.4. 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
  8.5. 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
  8.6. 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
  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. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? 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. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes