NSUP: Vitamin E (2014)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To study the coagulation effect of vitamin E on warfarin-induced vitamin K deficiency in rats and humans.
Inclusion Criteria:
  • 250g Sprague-Dawley male rats
  • Cardiology patients receiving warfarin on a long-term basis and who had mild to moderate prolongation of their prothrombin times (range 16 to 21.5 s)
  • Consented to take vitamin E supplement
  • No known liver disease
  • No vitamin E use.
Exclusion Criteria:
  • Rats:
    • Female rats
    • Breed other than Sprague-Dawley rats.
  • Humans:
    • Known liver disease
    • Prior or current vitamin E use.
Description of Study Protocol:


Subjects were recruited from cardiology offices.


The human studies were conducted on 12 adult cardiology patients receiving warfarin on a long-term basis. Patients were seen on a regular basis by a physician; blood was collected monthly for five months before the administration of vitamin E. The dose of vitamin E (alpha tocopherol 100 IU or 400 IU per day for four weeks) was randomly assigned by the clinical pharmacist. Blood samples were obtained weekly at the same time each week. Patients kept a diet record and warfarin doses were monitored. The control group was 50 adult patients without known liver disease or vitamin K deficiency. Prothrombin time, factor II coagulant activity and factor II antigen were measured.

In the animal studies, male rats were fed a standard rat chow diet. To induce vitamin K deficiency, rats were fasted for 24 hours, given warfarin (0.01mg to 1.0mg per 100g body weight). Blood was collected 24 hours later. Vitamin E was given in the dose of 100 IU per 100g body weight per day for seven days. Prothrombin time, factor II coagulant activity and factor II antigen were measured.


Vitamin E supplementation.

Statistical Analysis

  • T-test for non-paired experiments
  • P<0.05 was considered significant.
Data Collection Summary:

Timing of Measurements

  • Human subjects:
    • Blood collected monthly prior to vitamin E supplementation
    • Blood samples collected weekly at the same time each week during the four-week vitamin E intervention period and analyzed for prothrombin time, factor II coagulant activity and factor II antigen.
  • Rats: Blood collected prior to and after vitamin E intervention and analyzed for prothrombin time, factor II coagulant activity and factor II antigen.

Dependent Variables

  • Prothrombin time
  • Factor II coagulant activity using thromboplastin and Echis venom
  • Factor II antigen by electroimmunoassay of Laurel.

Independent Variables

Vitamin E supplementation.

Control Variables

  • Warfarin dose
  • Diet record
  • Medication use
  • Presence of clinical bleeding state.
Description of Actual Data Sample:
  • Initial N: A total of 12 human subjects (eight males, four females)
  • Attrition (final N): A total of 12 human subjects (eight males, four females).
Other Relevant Demographics
  • Cardiac diagnoses: Rheumatic heart disease in seven subjects, aortic stenosis in three subjects and atherosclerotic heart disease in two subjects
  • Warfarin use varied from two years to 17 years with mean of 6.2 years.


Arizona, United States.


Summary of Results:

Key Findings

  • Human study results:
    • Factor II antigen did not change throughout the testing period and were no different from normal adult controls
    • Factor II coagulant activity appeared to decline in both vitamin E treatment groups by the first week but differences were not significant (P>0.05)
    • The ratio of coagulant activity to antigen illustrated a significant change noted by two weeks in both treatment groups as compared to baseline.
  • Rat study results:
    • Rats were given doses of warfarin ranging from 0.01mg to 1mg per 100g body weight in order to determine the lead amount of the drug that would significantly depress the factor II coagulant, which was found to be 0.01mg
    • Rats receiving warfarin  and vitamin E demonstrated more severe reduction in factor II coagulant activity as measured with thromboplastin than those given warfarin without the vitamin (P<0.001); however, factor II activity using Echis venom was not reduced
    • Rats who were given vitamin E with and without warfarin did not have Echis factor II levels below untreated controls.

Data in Warfarin-treated Patients Receiving Vitamin E
Vitamin E (IU Day) Factor II Coagulant Activity (Percent of Normal Pool of Plasma) Factor II Antigen (Percent of Normal Pool of Plasma) Coagulant Activity:Antigen Ratio Prothrombin Time (Seconds)
None (baseline) 52±10 84±6 0.63±0.07 19±0.8
400 IU Week One 43±6 80±1.2 0.54±0.06 21±0.8
400 IU Week Two 36±2.5 85±5 0.42±0.03 
400 IU Week Three 33±4 80±4 0.41±0.04
400 IU Week Four 35±2 83±4 0.42±0.02
100 IU Week One 37±5 81±4 0.46±0.05 22±2
100 IU Week Two 36±3 83±3 43±0.03
100 IU Week Three 36±4 83±3 0.43±0.04
100 IU Week Four 37±6 83±7 0.45±0.06
Adult controls without warfarin 83±3 91±4 0.91+0.3  
Normal range 60 to 150 60 to 150 0.77 to 1.00  

Other Findings
  • No human subjects developed a clinical bleeding state
  • No human subjects had a change in diet or warfarin dose.


Author Conclusion:
Although the administration of high doses of vitamin E in animals, and possibly humans, with vitamin K deficiency potentiates the vitamin K deficiency, this effect is not clinically obvious with 400 IU day or less.
Funding Source:
Government: National Instiutes of Health
University/Hospital: University of Arizona Health Sciences Center
Reviewer Comments:
Although the author states that the diet remained consistent, an evaluation of vitamin K and Vitamin E intake was not described.
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) Yes
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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? 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
  3.2. 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? 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
4. Was method of handling withdrawals described? 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
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  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? 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.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? 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
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? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? ???
  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? Yes
  6.6. Were extra or unplanned treatments described? 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
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? ???
  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? 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
  8.1. 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)? 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
  8.7. 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? No
  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? Yes
  10.2. Was the study free from apparent conflict of interest? Yes