HTN: Vitamins (2007)
- Healthy persons with hypertension; HTN defined as a history of antihypertensive tx or untreated diastolic BP>90mm Hg on at least three occasions
- Non-hypertensive healthy persons for controls.
Recruitment
Subjects were recruited by advertisement.
Design
- At baseline all subjects were fasted overnight, did not smoke for 24 hours, antihyperstensive medications were maintained before and during the study
- Subjects were randomized to tx with one treatment of two grams of vitamin C or placebo followed by a blood sample and assessment of flow mediated brachial artery dilation, subjects were then treated with daily 500mg vitamin C or placebo for one month, treatment was doubly blinded
- Compliance was measured by tablet count and plasma ascorbic acid levels
- Non-hypertensive subjects were included as controls, thus there was a non-hypertensive and a hypertensive group receiving placebo and a non-hypertensive and a hypertensive group receiving vitamin C.
Blinding Used
Double-blind treatment.
Intervention
One-time dose of two grams vitamin C at baseline, followed by daily dose of 500mg vitamin C for one month.
Statistical Analysis- Baseline characteristics were compared using unpaired Sudent's T-test, chi-square test or Fisher's exact test
- Effect of tx was compared by two-way repeated-measures ANOVA with post-hoc Student-Newman-Keuls
- P< 0.05 was used to determine significance.
Timing of Measurements
At baseline, two hours after single dose of two grams vitamin C and one month later following intervention of daily placebo or 500mg vitamin C.
Dependent Variables
- SBP and DBP measured after 10 minutes of rest in a semirecumbent position, the average of three meaures was used
- Resting arterial diameter
- Reactive hyperemic flow
- Serum total and HDL-cholesterol, triglycerides and glucose measured using automated analyzer
- LDL-cholesterol calculated using Friedewald formula
- Plasma ascorbic acid concentrations.
Independent Variables
- 500mg vitamin C per day for one month
- Two grams vitamin C
- Compliance was measured by tablet count and plasma ascorbic acid levels.
- Initial N: 127 (82 healthy, 45 hypertensive)
- Attrition (final N): 121 (82 healthy, 39 hypertensive; 40 and 20 females, respectively).
Age
- 46±4 years (mean±SD) for healthy controls
- 48±12 for hypertensive subjects
- 49±13 for placebo groups
- 48±11 for treatment groups.
- 33 African-Americans were healthy controls, 20 were hypertensive
- 13 African-Americans were in placebo groups, seven were in treatment groups.
Other Relevant Demographics
None discussed.
Anthropometrics
- BMI of 27.8±6.6 for healthy controls
- 30.2±6.0 for hypertensives
- 31.1±5.6 for placebo groups, 29.1±6.5 for treated groups
- There was no difference between groups at baseline.
Location
Boston, MA.
Effect of Treatment on Brachial Artery, Hemodynamic Parameters and Blood Pressure
|
Placebo |
Placebo |
Placebo |
Vitamin C |
Vitamin C |
Vitamin C |
Systolic BP mmHg | 156±21 | 154±23 | 153±19 | 155±22 | 156±23 | 142±16* |
Diastolic BP mmHg | 88±14 | 86±13 | 84±14 | 87±9 | 84±12 | 79±8 |
Mean BPmmHg | 110±15 | 109±15 | 107±13 | 110±12 | 108±13 | 100±8* |
Resting arterial diam., mm |
4.0±0.7 | 4.0±0.7 | 4.0±0.7 | 4.1±0.8 | 4.2±0.7 | 4.2±0.8 |
Reactive hyperemic flow, % change | 568±295 | 593±319 | 455±259 | 591±256 | 581±224 | 696±354 |
*P<0.001 vs. baseline
Other Findings
No effect of vitamin C on measures of bioavailability of endothelium derived vasodilators (cGMP) or on urinary protaglandin F (a meaure of lipid peroxidation), or on serum total cholesterol, LDL-C, HDL-C, Tgs, or glucose was seen.
- A significant reduction in systolic and mean blood pressure was seen following one month of treatment with 500mg vitamin C
- Conduit vessel endothelial dysfunction secondary to hypertension is not reversed by acute or chronic treatment with oral ascorbic acid.
Government: | NHLBI |
University/Hospital: | Boston University School of Medicine |
- BP data previously published in 1999
- Results discussed in this publication focused on endothelial dysfunction and effect on brachial artery response
- Current paper did not differentiate between changes in BP between controls and hypertensive subjects
- No discussion of dietary control, exercise, or weight change during study
- Only one month treatment period considered chronic.
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? | ??? | |
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? | ??? | |
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) | No | |
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? | 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? | Yes | |
5.1. | In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? | Yes | |
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? | ??? | |
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? | 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? | No | |
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? | No | |
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? | No | |
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? | ??? | |
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)? | 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? | No | |
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 | |