HTN: Fiber (2007)
- Healthy participants from a primary-care health center
- Aged 25 - 64 years
- Without serious illnesses
- Cardiovascular diseases other than HTN
- GI disease
- Cancer
- Serious psychiatric disorders
- Hypercholesterolemia
- Patients who had undergone a recent traumatic event such as bereavement
- Those unable to give consent
- Using dietary supplements
- Pregnant or trying to conceive
Recruitment
Patients recruited from lists of 2 general practices based in a health center. Letters were sent out to patients from August 1997 - September 1998.
Design
Randomized Controlled Trial. Randomized using computer-generated randomization list.
Blinding used (if applicable)
Not possible - lab tests.
Intervention (if applicable)
Negotiation method to encourage an increase in fruit and vegetable consumption to at least 5 daily portions.
Statistical Analysis
Power calculation based on previous antioxidant data. Modified intention-to-treat analysis in which patients who were assigned but did not attend initial appointment were excluded. Comparisons between proportions were made with chi-square and between means with t test. Adjustment for covariates done with multiple regression analysis. Differences in outcome between intervention group and controls are shown with 95% confidence intervals.
Timing of Measurements
Participants attended 2 appointments at baseline and at 6 months with trained nurse. 2 weeks after initial intervention, research nurse telephoned to reinforce message. Letter sent at 3 months.
Dependent Variables
- Blood pressure taken by research nurses using electronic automatic sphygmomanometer
- Height and weight using stadiometer and scales
- Blood samples analyzed for antioxidant vitamins and total cholesterol concentrations
-
Fruit and vegetable intake assessed by DINE food frequency questionnaire
-
Overall intake assessed by Eating Pattern Assessment Questionnaire
Independent Variables
-
Negotiation method to encourage an increase in fruit and vegetable consumption to at least 5 daily portions.
-
Controls received intervention after 6 months
Control Variables
- Baseline antioxidant concentrations
- Sex
Initial N: 1045 of 2302 responded. 729 assigned to groups.
Attrition (final N): 690 healthy participants
Age: mean age Intervention Group: 45.7 +/- 10.1 years, Controls: 46.0 +/- 10.1 years
Ethnicity: Practices had few patients from ethnic minorities
Other relevant demographics:
Anthropometrics: There were substantially more men in the intervention group than controls, but groups were similar in age, social class and BMI.
Location: Thame, Oxfordshire, United Kingdom.
Variable | Between-Group Difference in Change | Adjusted Difference in Change | P for Adjusted Differences |
Alpha-carotene | 0.007 | 0.009 | 0.027 |
Beta-carotene |
0.027 |
0.031 |
0.005 |
Lutein | 0.018 | 0.018 | 0.032 |
Lycopene | -0.010 | -0.013 | 0.29 |
Beta-cryptoxanthin | 0.047 | 0.050 | 0.0002 |
Retinol | 0.001 | -0.008 | 0.73 |
Ascorbic Acid | 1.91 | 2.38 | 0.023 |
Alpha-tocopherol | 0.117 | 0.093 | 0.76 |
Alpha-tocopherol adjusted for cholesterol | 0.034 | 0.036 | 0.49 |
Gamma-tocopherol | -0.038 | -0.023 | 0.63 |
Gamma-tocopherol adjusted for cholesterol | -0.005 | 0.001 | 0.91 |
Total cholesterol | 0.018 | 0.010 | 0.86 |
Self-reported daily intake of fruits and vegetables | 1.3 | 1.4 | <0.0001 |
SBP | 3.4 | 4.0 | <0.0001 |
DBP | 1.4 | 1.5 | 0.02 |
Weight |
0.0 |
0.1 |
0.68 |
Other Findings
Plasma concentrations of alpha-carotene, beta-carotene, lutein, beta-cryptoxanthin, and ascorbic acid increased by more in the intervention group than in controls (significance ranging from p = 0.032 to 0.0002).
Groups did not differ for changes in lycopene, retinol, alpha-tocopherol, gamma-tocopherol, or total cholesterol concentrations.
Self-reported fruit and vegetable intake increased by a mean of 1.4 +/- 1.7 portions in the intervention group and by 0.1 +/- 1.3 portion in the control group (between group difference of 1.4, 95% CI: 1.2 - 1.6, p < 0.0001).
SBP fell more in the intervention group than in controls (difference of 4.0 mm Hg, 95% CI: 2.0 - 6.0, p < 0.0001) as did DBP (1.5 mm Hg, 95% CI: 0.2 - 2.7 mm Hg, p = 0.02).
Not-for-profit |
|
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? | 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? | Yes | |
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? | 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? | 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? | Yes | |
10.2. | Was the study free from apparent conflict of interest? | Yes | |