EAL

HTN: Potassium (2015)

Citation:

Berry SE, Mulla UZ, Chowienczyk PJ, Sanders TAB. Increased potassium intake from fruit and vegetables or supplements does not lower blood pressure or improve vascular function in UK men and women with early hypertension: A randomised controlled trial. Br J Nutr. 2010; 104: 1,839-1,847.

PubMed ID: 20673378

Study Design:

Randomized Crossover Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To test the effects on BP and vascular function of increasing potassium intake from usual levels by increased intake of fruit and vegetables or by supplementation in subjects with high-normal or elevated BP who were not receiving BP-lowering medication.

Inclusion Criteria:

Seated DBP higher than 80mm Hg and less than 100mm Hg on two occasions.

Exclusion Criteria:

Clinical history of:
- Myocardial infarction
- Diabetes
- Renal disease
- Gastrointestinal disease
- Pancreatitis
- Cholestatic liver disease
- Cancer.
Current use of:
- Systemic corticosteroids
- Androgens
- Phenytoin
- Erythromycin
- Thyroid hormones
- Lipid-lowering, BP-lowering or anticoagulant medication
Cigarette smoking
History of substance abuse or alcoholism
Alcohol intake of more than 24g to 36g per day
Pregnancy or baby within the last year
Allergy or intolerance to intervention foods
Unwillingness to refrain from use of dietary supplements
Weight loss of more than 3kg in the preceding two months
BMI less than 20kg/m² or more than 35kg/m²
BP and other risk factors making them eligible for drug treatment.

Description of Study Protocol:

Recruitment

Recruited in three cohorts between October 2004 and November 2005
Advertisements and flyers at higher educational institutions.

Design

Randomized crossover trial.

Blinding Used

Implied with measurements
Participants blinded to potassium capsules or placebo
Staff conducting vascular measurements blinded to treatment allocation.

Intervention

Three experimental treatments and control treatment
Three-week run-in on control level of fruit and vegetable intake, providing 15mmol per day
Each treatment was six weeks long, each separated by five-plus weeks of usual diet
Compliance to the intervention was corroborated by food intake records and increased urinary potassium excretion
Study provided fruit and vegetables during treatment periods:
- 20mmol per day potassium as fruit and vegetables
- 40mmol per day potassium as fruit and vegetables
- 40mmol per day potassium citrate
- Placebo capsules and intake of fruit and vegetables similar to average UK intake.

Statistical Analysis

Sample size calculation to detect 4mm Hg change in SBP in sample of 32 subjects
Intention to treat analysis on 48 participants who completed study
Repeated measures ANOVA of four treatments, with run-in as covariate
Post hoc comparisons made between treatment levels when overall F indicated a significant between-treatment effect
Change from control value shown with 95% CI corrected for multiple comparisons (Bonferroni)
Non-parametric tests to analyze CRP
Spearman's correlations between five within-subject measures.

Data Collection Summary:

Timing of Measurements

Baseline and last week of each study period.

Dependent Variables

Change in 24-hour ambulatory BP recorded at 30-minute intervals during the day and one-hour intervals at night
Mediated dilatation of brachial artery measured in right arm
Endothelial independent dilation measured in response to 25mcg trinitrate
Total cholesterol, HDL-C, TAG, glucose, insulin, CRP, carotenoids, tocopherols, folate, homocysteine
Urinary sodium and potassium.

Independent Variables

Four treatment periods for six weeks each, with compliance to the intervention corroborated by food intake records and increased urinary potassium excretion:

20mmol per day potassium as fruit and vegetables
40mmol per day potassium as fruit and vegetables
40mmol per day potassium citrate
Placebo capsules and intake of fruit and vegetables similar to average UK intake.

Description of Actual Data Sample:

Initial N

N=57 (gender not specified).

Attrition (Final N)

N=48 (23 males, 25 females):

Grade One hypertension: N=23
High-normal BP: N=18
Normal BP: N=7.

Age

Males: 45.5±10.6 years
Females: 44.8±8.2 years.

Ethnicity

Males: 70% white European, 4% Black African, 26% Asian
Females: 52% white European, 36% Black African, 1% Asian.

Anthropometrics

Baseline BP (mm Hg):
- Males:
  - SBP: 139.4±9.7
  - DBP: 88.0±6.6.
- Females:
  - SBP: 136.0±9.1
  - DBP: 89.2±5.7.
BMI (kg/m²):
- Males: 27.7±3.2
- Females: 29.2±4.3.

Location

United Kingdom.

Summary of Results:

Key Findings

There were significant increases in urinary potassium during intervention periods compared with control. The increments with 40mmol fruit and vegetables and 40mmol potassium citrate were not significantly different.
Changes in ambulatory BP, arterial stiffness and endothelial function during intervention periods were not significantly different from the control period
Analysis of those with Stage One hypertension only did not result in significant differences.

Author Conclusion:

These results do not provide support for dietary advice to increase potassium intake above levels habitually consumed in the UK for subjects with early hypertension.

Funding Source:

Government:

Food Standards Agency (UK)

Not-for-profit

Guy's and St. Thomas' NHS Foundation Trust in partnership with King's College, London

Other non-profit:

Reviewer Comments:

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?	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?		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