HTN: Vitamins (2007)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine the effect of vitamin C supplements on ambulatory blood pressure and plasma lipids.
Inclusion Criteria:
- 60 to 80 years old
- Non-smokers for over 10 years
- No hx of vascular disease, i.e., stroke, MY, angina, peripheral vascular disease
- Not taking prescribed medications including aspirin, non-steroidal anti-inflammatory drugs or vitamin supplements
- Normotensive, hx of borderline HTN or newly diagnosed HTN, but never having received treatment.
Exclusion Criteria:
None specified.
Description of Study Protocol:
Recruitment
Subjects were recruited from general practice lists.
Design- Randomized placebo-controlled crossover study
- Baselne measures of weight, BP, plasma ascorbic acid and lipids were conducted
- Subjects were randomized to treatment or placebo for three months
- After a one-week washout period, subjects were crossed over to the alternative treatment for three more months.
Blinding Used
Treatment was doubly-blinded.
Intervention
250mg vitamin C twice daily for three months.
Statistical Analysis
- A power analysis was conducted to obtain a power of 80% at the 5% significance level to detect changes in systolic BP of at least three mm Hg and HDL-C of at least 0.1mmol per L
- Regression analysis was used to determine the effect of vitamin C on difference in BP and lipid levels between placebo and active phases of the study
- Treatment periods, sex, weight change and baseline BP were variables included in the analysis.
Data Collection Summary:
Timing of Measurements
- Measurement of weight, BP and serum lipids were taken at baseline
- BP was measured monthly during the study including at the end of each three-month study period
- Plasma lipids and ascorbic acid were measured at the end of each three-month study period.
Dependent Variables
- Systolic and diastolic BP measured in sitting position with a sphygomanometer
- Systolic and diastolic BP measured using home 24-hour ambulatory method with measures every 15 minutes
- Plasma lipids including TC, LDL-C, and HDL-C.
Independent Variables
- 250mg vitamin C taken as capsules twice daily (500mg total daily)
- Matched placebo.
Description of Actual Data Sample:
- Initial N: 40 (20 men)
- Attrition (final N): 40; data from two participants demonstrated <10% change in plasma ascorbic acid from placebo to vitamin C phases of the study, however analysis with and without this data was not different.
- Age: 72±4 years (mean±SD)
- Ethnicity: Not discussed
- Other relevant demographics: None discussed.
- Anthropometrics: Weight decreased from baseline to intervention phases by 0.47kg (P=0.06), but there was no change beween placebo and vitamin C phases (73.2±12.7 vs. 73.2±12.9kg).
- Location: UK.
Summary of Results:
Mean BP During Each Phase of the Study (mean±SD)
All Subjects (N=40)
|
|
Baseline
|
Placebo
|
Vitamin C
|
BP Measured in Clinic
|
SBP
|
142±15
|
143±15
|
142±16
|
|
DBP
|
88±9
|
87±8
|
86±8
|
Ambulatory Day-time BP
|
SBP
|
135±15
|
136±18
|
134±14*
|
|
DBP
|
79±9
|
79±9
|
78±6
|
Night-time BP
|
SBP
|
122±15
|
122±14
|
122±14
|
|
DBP
|
68±9
|
68±7
|
68±7
|
HTN Subjects (N=17)
Ambulatory Day-time |
SBP
|
149±10
|
150±7
|
146±8*
|
|
DBP
|
84±10
|
83±8
|
81±7
|
Normotensive Subjects (N=23) Ambulatory Night-time
|
SBP
|
125±9
|
125±8
|
125±9
|
|
DBP
|
75±6
|
75±5
|
76±4
|
*P≤0.05
Other Findings
- Sitting clinic BP did not change between vitamin C and placebo phases
- Daytime ambulatory SBP decreased by 2.0±5.2 mm Hg, 95% CI 0.0-3.9 mm Hg, following vitamin C supplementation
- Plasma ascorbate levels during placebo and treatment phases or change in ascrobate between the phases was not associated with change in SBP
- Increased baseline daytime BP was associated with greater decreases in BP following vitmain C supplementation (coefficient for SBP: 0.19, P=0.03, R2=15% and DBP coefficient: 0.20, P=0.02, R2=14%)
- There was no difference between placebo and treatment groups for serum lipids , with the exception of an increase in HDL for women, following vitamin C supplementation, 0.08±0.11mmol, P=0.007.
Author Conclusion:
In older adults high intakes of vitamin C for three months may lower elevated systolic BP.
Funding Source:
University/Hospital: | University of Leicester, Glenfield Hospital, University of Surrey (all UK) |
Reviewer Comments:
- Smoking, exercise, diet, ethnicity were not discussed
- Measurement of compliance with the vitamin C supplement took place at baseline and completion of the three-month intervention phase by plasma ascorbic acid levels
- Pill-counting was used, however this did not determine if the vitamin C was taken regularly during the entire treatment phase
- A strength is the crossover design.
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? | ??? | |
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? | 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? | 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? | 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? | 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? | 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? | 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? | Yes | |
9. | Are conclusions supported by results with biases and limitations taken into consideration? | Yes | |
9.1. | Is there a discussion of findings? | Yes | |
9.2. | 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? | ??? | |
10.2. | Was the study free from apparent conflict of interest? | Yes | |