VN: Vitamin B-12 (2011)

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

To determine the role of genetic factors in the development of hyperhomocysteinemia.

Inclusion Criteria:

Not described

Exclusion Criteria:

Not described

Description of Study Protocol:


Combination of data from three study populations:

  • Lacto-/lacto-ovo vegetarians and vegans
    • N=111
    • Median age: 46±15 years
  • Healthy seniors
    • N=118
    • Mean age: 82±6.5 years
  • Healthy younger control group
    • N=98
    • Mean age: 25±8 years.



Blinding used

Not described

Statistical Analysis

Differences between genotypes tested using Kruskal-Wallis test. Multi-factorial ANOVA was used to identify the influence of confounders on homocysteine concentration. A priori alpha set at P<0.05.

Data Collection Summary:

Timing of Measurements

Not reported

Dependent Variables

  • Homocysteine
  • Serum MMA
  • Serum B12
  • Serum folate
  • Serum HoloTC-II.

Independent Variables


Control Variables

Age group (seniors vs. younger adult)

Description of Actual Data Sample:
  • Initial N: Initial N's from original studies not specified
  • Attrition (final N): 327
    • 111 lacto-/lacto-ovo vegetarians and vegans
    • 118 healthy seniors
    • 98 healthy younger controls
  • Age:
    • Lacto-/lacto-ovo vegetarians and vegans: 46±15 years
    • Healthy seniors: 82±6.5 years
    • Healthy younger control group: 25±8 years
  • Ethnicity: Not described
  • Location: Not described.
Summary of Results:

Key Findings

Median (5th, 95th percentiles) of B12, MMA and Holo-TCII by Genotype Group

B12 (pg/ml)

  • Vegetarians
    • TC C/C: 270 (154-442)
    • TC C/G: 260 (159-600)
    • TC GG: 261 (147-489)
    • COMT G/G: 287 (155-928)
    • COMT G/A: 260 (166-479)
    • COMT A/A: 227 (140-416)
  • Seniors
    • TC C/C: 409 (187-937)
    • TC C/G: 371 (235-1,152)
    • TC GG: 348 (180-775)
    • COMT G/G: 358 (226-1,008)
    • COMT G/A: 370 (204-829)
    • COMT A/A: 330 (181-495)

MMA (nmol/l)

  • Vegetarians
    • TC C/C: 311 (162-1,590)
    • TC C/G: 366 (145-2,761)
    • TC GG: 362 (143-2,036)
    • COMT G/G: 235 (121-1,767)
    • COMT G/A: 435 (145-2,278)
    • COMT A/A: 368 (166-3,072)
  • Seniors
    • TC C/C: 228 (235-1,152)
    • TC C/G: 224 (115-953)
    • TC GG: 291 (114-1,918)
    • COMT G/G: 223 (99-772)
    • COMT G/A: 236 (114-748)
    • COMT A/A: 294 (123-986)
    • HoloTC-II (μmol/L)
  • Vegetarians
    • TC C/C: 32 (2-69)
    • TC C/G:20 (2-105)
    • TC GG:24 (4-122)
    • COMT G/G:35 (4-266)
    • COMT G/A: 21 (2-97)
    • COMT A/A: 21 (2-53)
  • Seniors
    • TC C/C: 55 (4-110)
    • TC C/G:45 (16-252)
    • TC GG:53 (8-186)
    • COMT G/G: 70 (17-158)
    • COMT G/A: 43 (9-271)
    • COMT A/A: 49 (13-96).
Author Conclusion:

"Among the variants of 15 genes involved in homocysteine metabolism, the MTHFR 677C→T is the major determinant of plasma homocysteine level. In our study this effect was most obvious in vegetarians. In vegetarians vitamin B12 deficiency increased the susceptibility of hyperhomocysteinemia in mutation carriers."

Funding Source:
Other: Not reported
Reviewer Comments:
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) N/A
  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? No
2. Was the selection of study subjects/patients free from bias? 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? No
  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? No
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) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) ???
  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.) No
  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? No
  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? No
  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
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) 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
  6.8. 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
  7.1. 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
  7.3. 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
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? N/A
  7.7. Were the measurements conducted consistently across groups? N/A
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? No
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes