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VN: Micronutrients in Pregnancy (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

The aim of the study was to compare serum vitamin B-12 and homocysteine concentrations in pregnant women consuming vegetarian and Western diets and to evaluate the adequacy of current dietary reference intakes of vitamin B-12 for these women.

Inclusion Criteria:

Subjects in vegetarian and low meat groups were included only if they had not changed their diet substantially for at least 3 years.
Exclusion Criteria:
Not described
Description of Study Protocol:

Recruitment

Recruitment and selection of subjects is described in Koebnick, C., Heins, U. A., Hoffmann, I., Dagnelie, P. C. & Leitzmann, C. (2001) Folate status during pregnancy in women is improved by long-term high vegetable intake compared with the average western diet. J. Nutr. 131: 733–739.

Subjects were recruited via announcements in health magazines and from study information handed out by their gynecologists.

Design

3 diet groups:

  1. women adhering to a plant-based diet (defined as characterized by a high consumption of raw vegetables (>100 g/d), preference of whole-grain products (ratio of refined grain products/whole-grain products <0.95) and limited meat consumption (meat <300 g/wk; meat products <105 g/wk)., subdivided into:
    • ovo-lacto vegetarians (completely omitted meat and meat products from their diets.)
    • low-meat eaters,
  2. women consuming an average Western diet (control group--similar to that of the average German population)

Data on diet and blood concentrations of erythrocyte folate, tHcy, serum vitamin B-12 gathered in each trimester.

Blinding used:

Intervention: Not applicable, observational study

Statistical Analysis

Statistical analyses were performed using SAS 8.2 (SAS Institute). All values are arithmetic means ± SEM or medians with 25th and 75th percentiles in parentheses. BMI was calculated as reported pregravid weight/height (kg/m2).

Generalized estimating equation (GEE) procedure was used. GEE models were generated to allow an appropriate analysis of longitudinal data with repeated measurement and missing values. Logistic regression analysis with repeated measurement design (GEE), and odds ratios and 95% confidence intervals were calculated.

Data Collection Summary:

Timing of Measurements

Information on dietary intake and blood samples were collected in each trimester of pregnancy (week 9–12, 20–22 and 36–38 of gestation, i.e., postmenstruation).

Dependent Variables

  • tHcy in plasma
  • Serum vitamin B-12 concentrations

Independent Variables

  • nutritional behavior (questionnaire )
  • food consumption (semi-quantitative 4 day food frequency list, considering the usual dietary intake before pregnancy)
  • dietary folate and vitamin B-12 intake (calculated using the German Food Code and Nutrition Data Base BLS II.3)

Control Variables: none

Description of Actual Data Sample:

Initial N: 109 women; 70 women consuming a plant-based diet (27 ovo-lacto vegetarians, 43 low-meat eaters) and 39 controls.

Attrition (final N): Only 60 subjects were assessed 3 times throughout pregnancy.

Age: (as Means ± SEM measured at beginning of pregnancy)

  • Lacto-ovo vegetarian 30.8 ± 0.9
  • Low Meat Eaters 30.6 ± 0.6
  • Western Diet 29.1 ± 0.6

Ethnicity: Not reported

Other relevant demographics: Ovo-lacto vegetarians and low-meat eaters had similar mean age and parity as control group, but showed lower prepregnancy BMI and marginal differences in smoking habits.

Anthropometrics (e.g., were groups same or different on important measures)

Location: Germany

Summary of Results:

B-12 Intake

Vitamin B-12 intake during pregnancy2

Ovo-lacto Vegetarians (OLV)

Low Meat Eaters (LME)

Control

Significance

Total dietary intake (micrograms per day)

2.5 (1.3–3.8)

3.8 (3.0–4.9)

5.3 (4.3–6.3)

p<0.001 (OLV v. control)

p<0.001 (LME v. control)

From milk, yogurt, cheese

2.1 (0.1–3.2)

2.3 (1.8–3.0)

2.0 (1.4–2.6)

P=0.569 (OLV v. control)

P= 0.102 (LME v. control)

From meat, fish, eggs

0.3 (0.0–0.5)

1.3 (0.7–2.0)

3.2 (2.2–4.1)

P<0.001 (OLV v. control)

P<0.001 (LME v. control)

Vitamin B-12 supplement user (%)

32.1

27.9

20.5

P=0.889 (OLV v. control)

P=0.559 (LME v. control)

The diet groups differed significantly with regard to dietary vitamin B-12 intake in all trimesters of pregnancy. Intake was lowest in the ovo-lacto vegetarian group, highest in the control group, with the low meat group falling between.

The estimated average vitamin B-12 requirement (2.2 micrograms/day) met by each group was significantly different (p<.001) throughout preganancy:

  • 60% of ovo-lacto vegetarians
  • 94% of low-meat eaters
  • 100% or the control group

Blood Values

Serum vitamin B-12 concentrations: For all groups serum vitamin B-12, holo-TC, and holo-HC concentrations decreased during pregnancy (P <0.001)

  • serum vitamin B-12 concentrations of ovo-lacto vegetarians and lowmeat eaters were lower than those of the control group (P<0.001 and P<0.050 respectively).
  • Holo-HC concentrations were lower in ovo-lacto vegetarians than in the control group (P 0.009)
  • Holo-HC concentrations in low-meat eaters and the control group did not differ significantly

  • odds ratio of having a low serum vitamin B-12 levels in at least 1 trimester was 3.9 (95% CI, 1.9–6.1) for ovo-lacto vegetarians and 1.8 (1.0 –3.9) for low-meat eaters, using the control group as a reference.

Plasma total homocysteine

  • Over the total pregnancy, plasma tHcy concentrations were higher in ovo-lacto vegetarians than in the control group (P<0.032) and tended to be higher in the low-meat eaters than in the control group (P<0.061).
  • The frequency of elevated plasma tHcy concentrations did not differ among the diet groups.
  • Elevated concentrations of plasma tHcy combined with low serum concentrations of vitamin B-12 were observed in at least 1 trimester in 25.0% of ovo-lacto vegetarians, in 10.0% of low-meat eaters, and in 2.6% of controls (P<0.003).

Relation among Vitamin B-12 Intake, Serum B-12, and tHcy

  • the strongest predictors of serum vitamin B-12 concentrations were:
    • milk and dairy products (GEE estimate ±SE for log serum vitamin B-12 (log mmol/L): 0.0190±0.0085; P=0.026)
    • supplements (0.0212±0.0101, P=0.036)
    • meat and fish (0.0016±0.0015, P=0.073)
  • the strongest predictors of plasma tHcy concentrations were:
    • intake of vitamin B-12 from meat and fish (GEE estimate ±SEE for plasma tHcy (micromol/L): -0.1778±0.0587, P=0.003)
    • supplements (-0.2610±0.0873, P=0.003)
    • vitamin B-12 from milk and dairy products only marginally predicted plasma tHcy (-0.1962±0.1191, P=0.099).
  • In ovo-lacto vegetarians, serum vitamin B-12 predicted 61% of plasma tHcy variation, in low-meat eaters 11%, and in controls 6%.
  • Serum vitamin B-12 concentrations were:
    • positively associated with total dietary vitamin B-12 (GEE estimate of log-B-12 ±SEE for (micrograms/d):1.1180±0.03098; P=0.003)
    • negatively associated with plasma tHcy concentrations (GEE estimate of tHcy ±SEE for (micrograms/d): -1.6096±0.7113; P=0.024)

There were no significant interactions between intake of vitamin B-12 from different food groups and diet group.

For all groups plasma tHcy concentrations were inversely related to both serum vitamin B-12 (GEE estimate of log-B-12 ±SEE for plasma tHcy (micromol/L): -2.6842±0.8636; P=0.002) and erythrocyte folate concentrations (-0.0016±0.0007; P=0.023).

An interaction between diet group and serum vitamin B-12, suggests a greater effect of serum vitamin B-12 concentrations on tHCY in ovo-lacto vegetarians (P=0.032).

Author Conclusion:

"The present study shows that a long-term ovo-lacto vegetarian diet resulted in lower serum vitamin B-12 and higher plasma tHcy concentrations during pregnancy and therefore in an increased risk of vitamin B-12 deficiency. The present data also suggest that the current dietary reference intakes are too low and that an optimal dietary intake of vitamin B-12 during pregnancy should be at least above 3 micrograms vitamin B-12/d."

"Since fetal and maternal serum vitamin B-12 concentrations are strongly related, low intake of vitamin B-12 may result in a vitamin B-12 deficiency in newborns."

Funding Source:
Reviewer Comments:

Strengths

  • both comparison group and control group were used

Limitations:

  • Small group sizes after dropouts
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? No
  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
  2.2. 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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
  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? Yes
  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
  3.3. 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.) N/A
  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
  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. Was method of handling withdrawals described? No
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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? No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? No
  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? No
5. Was blinding used to prevent introduction of bias? No
  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.) No
  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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  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? No
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? No
  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? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  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? Yes
  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
  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? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  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? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  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)? No
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  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