Cardiovascular Disease and Micronutrients
To test the effect of vitamin E and C supplements, in moderate doses, on the progression of carotid atherosclerosis in men and post-menopausal women with hypercholesterolemia.
Hypercholesterolemia (serum cholesterol at least 193mg per dL)
- Regular intake of antioxidants, acetosalicylate or other drugs with antioxidant properties
- Severe obesity (BMI above 32kg/m2)
- Type 1 diabetes
- Uncontrolled hypertension (sitting diastolic blood pressure above 105mmHg)
- Any condition limiting mobility
- Severe disease shortening life expectancy
- Pre-menopausal women
- Women taking oral estrogen therapy.
- Recruitment: Volunteers were screened over the phone and eligible persons were invited to participate
- Design: Randomized clinical trial
- Blinding used: IMT measurement technician was blinded to participant supplementation. First three years of study were double-blinded. Second three years were open study.
Intervention
First three years of study:
- 91mg per day alpha-tocopherol (corresponding to 100mg per day alpha-tocopheryl acetate and 136 IU vitamin E), twice daily
- 250mg slow-release ascorbic acid, twice daily
- Both 91mg per day alpha-tocopherol and 250mg slow-release ascorbic acid in a single tablet, twice daily
- Placebo, twice daily.
Study Years Three through Six:
- All supplemented subjects receive supplement combination (91mg per day alpha-tocopherol and 250mg slow-release ascorbic acid in a single tablet, twice daily
- Placebo subjects receive no supplementation.
Statistical Analysis
- Intention-to-treat included 440 participants for whom ultrasound examination was available at six years
- Subjects randomized in strata and a priori power calculations based on analysis in men. Statistical analysis also done in men and women separately.
- Non-parametric Mann-Whitney test to examine differences between treatment groups
- General linear modeling of SPSS 10.0 for Windows for comparisons taking into account covariates
- Two-sided P-values
- Linear regression slope of the mean CCA-IMT over all points of follow-up time was used as the primary outcome measure
- Mean CCA-IMT from the right and left side was averaged, then slope computed across time-specific means
- Simple difference between the final mean IMT at 72 months and baseline mean IMT calculated for confirmation.
Timing of Measurements
- Common carotid artery intima-media thickness was measured at baseline and follow-up visits at six, 12, 18, 24, 30, 36 and 72 months
- Ascorbic acid measured by high-pressure liquid chromatography
- Alpha-tocopherol measured by reversed phase high-pressure liquid chromatography
- Plasma F2-isoprostane concentrations measured by gas chromatography-mass spectrometry
- Concomitant diseases and medications recorded at study Years Zero, One, Three and Six.
Dependent Variables
Common carotid artery intima-media thickness measured by high-resolution ultrasonography: Severity of atherosclerosis classified using four-categorical scale separately for right and left common carotid artery.
Independent Variables
- 91mg per day alpha-tocopherol, twice a day
- 250mg slow release ascorbic acid, twice a day
- Both 91mg per day alpha-tocopherol and 250mg slow-release ascorbic acid, twice a day (the only independent variable tested in Years Three to Six)
- Placebo (unsupplemented in Years Three to Six).
Control Variables
- Gender
- Baseline mean CCA-IMT
- Classification of severity of right and left CCA
- Baseline vitamin C concentration
- Three indicator variables for summer baseline examination months.
- Initial N: 520 (256 males, 264 post-menopausal females)
- Attrition (final N): 440 (212 men, 228 women) completed the study and six-year ultrasound re-examination. Of the 390 subjects randomized to supplementation, 335 continued study after three years and 256 (76.4%) adhered to supplements for six years.
- Age: Middle-aged (45 to 69 years)
- Ethnicity: Danish, Finnish and Swedish
- Other relevant demographics: None given
- Anthropometrics: Not given except BMI above 32kg/m2 excluded
- Location: Denmark and Finland.
Mean Annual Increase of the Mean Common Carotid Artery Intima-Media Thickness (CCA-IMT) | Supplemented Subjects (vitamins C+E) | Non-supplemented Subjects | Statistical Significance |
Linear slope across study period |
0.0118±0.0136mm |
0.0156±0.0182mm |
P=0.007 |
Simple difference between 72-month and baseline |
0.0103±0.014mm
|
0.0134±0.016mm
|
P=0.007 |
Other Findings
CCA-IMT progression
- Small reduction in mean CCA-IMT during first year of study, after which CCA-IMT started to progress linearly. Lines began to diverge after first year.
- Among those who took their supplements (N=256), the CCA-IMT linear slope was 0.0111mm per year (29% treatment effect, P=0.004)
- Among those who took their supplements (N=256), the CCA-IMT simple difference between 72-month and baseline assessments was 0.0095±0.012mm per year
- In men, difference between treatment groups in slope (P=0.008) and difference (P=0.002) was statistically significant. In women, neither was statistically significant.
- In both men and women combined, there was a 26% treatment effect in slope (95% CI, 5 to 46; P=0.014) and a 30% treatment effect in those who took their supplements (95% CI, 10 to 51; P=0.003)
- In all men, treatment effect in slope was 33% (95% CI, 4 to 62; P=0.024) and in all women, 14% (95% CI, -11 to 44, not significant)
- Among compliant men, treatment effect was 39% (95% CI, 9 to 69, P=0.019).
- Among compliant women, treatment effect was 17% (95% CI, -11 to 44, P=0.235).
- IMT mean simple difference in men and women combined was 0.0137mm in the non-supplemented group and 0.0102mm in the supplemented group, a 25% treatment effect (95% CI, 2 to 49; P=0.034)
- In men, the average annual increase of CCA-IMT was 0.0162mm in the non-supplemented group and 0.0103mm in the supplemented group, a 37% treatment effect (95% CI, 4 to 69; P=0.028). Difference was not significant in women.
- Treatment effect was greater in participants who already had plaques in CCAs at baseline (54% in those who had at least one plaque obstructing greater than 20% arterial lumen)
- Treatment effect also larger in those with low baseline vitamin C plasma levels
- Six-year change in mean CCA-IMT was inversely correlated with change in plasma alpha-tocopherol concentration in men, but not women.
36-month change in F2-Isoprostane concentrations
- In men, F2-Isoprostane concentration was significantly reduced in vitamin E group, but was increased in placebo and vitamin C groups: Treatment effect of vitamin E (mean -6.2ng per L; 95% CI, -2.2 to -10.2) was statistically significant (P=0.003, N=100)
- In women, F2-Isoprostanes decreased more in placebo group than in either vitamin E or C groups.
36-month change in HDL-cholesterol
- Mean HDL-cholesterol increased more significantly at three years in men who received vitamin C supplement than placebo (P=0.025)
- Vitamin E had no effect on HDL-cholesterol in men
- Neither vitamin E nor C had any effect on HDL in women.
This trial showed that long-term vitamin E and slow-release vitamin C supplementation combined, in reasonable doses, can slow the progression of common carotid atherosclerosis, especially in men.
University/Hospital: | Academy of Finland |
In-Kind support reported by Industry: | Yes |
Quality Criteria Checklist: Primary Research
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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? | No | |
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? | No | |
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? | No | |
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? | 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? | No | |
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? | 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? | 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 | |
7.6. | 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)? | 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? | No | |
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 | |