EAL

HTN: Diet Patterns (2015)

Citation:

Huggins CE, Margerison C, Worsley A, Nowson CA. Influence of dietary modifcations on the blood pressure response to antihypertensive medication. Br J Nutr. 2011;105:248-255.

PubMed ID: 20807467

Study Design:

Randomized Crossover Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

NEUTRAL: See Quality Criteria Checklist below.

Research Purpose:

To examine whether the low sodium and high potassium diet (LNAHK) and the DASH-type diet (OD) lowered blood pressure in subjects on antihypertensive therapy compared with those not on antihypertensive therapy.

Inclusion Criteria:

Over the age of 25 years
Systolic blood pressure of 120mm Hg or more or 80mm Hg or more for diastolic blood pressure at their second visit, or home systolic blood pressure 116mm Hg or higher or 78mm Hg or higher
Participants who were taking antihypertensive medication, provided they were willing to maintain their current level of antihypertensive therapy
Provided written informed consent.

Exclusion Criteria:

Systolic blood pressure higher than 160mm Hg and 90mm Hg for diastolic blood pressure
Cardiovascular event in the past six months
Insulin-dependent diabetes
On medications such as Warfarin or Dilantin
Ate their main meal outside the home more than twice per week
Planning to quit smoking or change smoking habits or were unwilling to cease taking dietary supplements, including vitamins, for the duration of the study.

Description of Study Protocol:

Recruitment

Subjects were part of a long-term prospective cohort study that was previously described.

Design

Sub-analysis of a prospective cohort study.

Statistical Analysis

Data were analyzed using SPSS for Windows (v 17.0)
ANOVA was used to assess the difference in blood pressure between the control diet and test diet phases (within-group factor) across the medication groups (between group factor)
A Sidak's T-test was used for post-hoc analysis
One-way ANOVA was used to evaluate the difference in changes in BP between the OD and LNAHK diet phases
P<0.05 was considered to be significant
Data are expressed as means and standard deviations.

Data Collection Summary:

Timing of Measurements

24-hour urine collections every two weeks
Blood pressure measured at same time every day using an automated BP monitor.

Dependent Variables

Blood pressure (BP):

Home BP was measured using an automated BP monitor on the left arm and data were either directly downloaded via a computer or recorded manually
Subjects were trained to correctly apply the cuff and instructed to take their BP measurements alone at the same time of the day after five minutes rest in a quiet room, taking three measurements in one-minute intervals.

Independent Variables

Control diet: A low-potassium and low-calcium diet
OD diet: Higher in potassium, magnesium and calcium and lower in saturated fat, with a moderate reduction in sodium together with increased fish intake. This diet was based on the United States DASH study and was rich in vegetables, fruits and reduced-fat dairy products.

Description of Actual Data Sample:

Initial N: 94 (38 female, 56 male) (N=52 on no therapy, 15 on RAS therapy and 27 on other antihypertensive therapy)
Attrition (final N): 94
Age:
- Mean age in no-therapy group: 52.1
- Mean age in RAS therapy group: 58.7
- Mean age in other therapy group: 61.7.
Anthropometrics: Mean BMI (kg/m²) in no-therapy group: 28.2 vs. 31.1 in RAS therapy group vs. 29.5 in other-therapy group.

Summary of Results:

Key Findings

The LNAHK diet produced a greater fall in systolic BP (SBP) in those on antihypertensive therapy (-6.2mm Hg) than in those not on antihypertensive therapy (-2.8mm Hg) (P=0.036); this was greatest for those on renin-angiotensin system (RAS) blocker therapy (-9.5mm Hg) (interaction P=0.007)
The fall in DBP on the LNAHK diet was not significantly different between those on therapy and those not on therapy
The fall in systolic blood pressure on the DASH-type diet in those on therapy was not as marked as that observed on the LNAHK diet (overall -1.1mm Hg vs. renin therapy -4.2mm Hg).

Author Conclusion:

Dietary modifications are an important part of all hypertension management regimens and a low-sodium and high-potassium diet enhances the blood pressure-lowering effect of antihypertensive medications, particularly those targeting the renin angiotensin system (RAS).

Funding Source:

Other:

Dairy Research and Development Corporation

Reviewer Comments:

Limitation:

Participants were classified post-hoc and therefore the sample size across the groups was unbalanced.

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?		No
	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?	No
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?	Yes
	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?		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.)	No
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	No
	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?	Yes
	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?	Yes
	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)?	No
	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?	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