EAL

DLM: Diet Composition (2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To evaluate the (independent) effect of sodium intake on dietary lipids.

Inclusion Criteria:

Adults ages 22 or more years
Hypertensive (average of three visits):
- BP systolic: 120 to 159mm Hg
- BP diastolic: 80 to 95mm Hg
Target was to enroll 50% women and 50% African Americans.

Exclusion Criteria:

History of CVD or renal insufficiency
Total cholesterol higher than 260mg per dL
Insulin dependency or poorly controlled T1DM or T2DM
Special dietary requirements
Current EtOH intake more than 14 drinks a week.

Description of Study Protocol:

Recruitment

Participant in the DASH diet study (Svetkey FM, Vollmer WM et al, N Engl J MEd. 2001; 344: 3-10).

Design

Two diets with varying amounts of sodium were studied:

A typical American control diet (higher fat, saturated fat and cholesterol; lower in fiber, calcium, potassium, magnesium)
The Dietary Approaches to Stop Hypertension (DASH) diet (abundant in fruits, vegetables, low-fat dairy products), which is associated in prior published research with significant reduction in blood pressure.

All subjects had an initial two-week "washout" period on the high-sodium control diet followed by randomization for 90 days to the control or DASH diets, each prepared with three levels of sodium (targeted at 50, 100, and 150mmol per day per 2,100kcal).

In total there were six participant groups:

Control (with 50mmol per day Na+ per 2,100kcal)
Control (with 100mmol per day Na+ per 2,100kcal)
Control (with 150mmol per day Na+ per 2,100kcal)
DASH (with 50mmol per day Na+ per 2,100kcal)
DASH (with 100mmol per day Na+ per 2,100kcal)
DASH (with 150mmol per day Na+ per 2,100kcal).

Intervention

Dietary modulation of Na+ intake as discussed above.

Statistical Analysis

A generalized estimating equations (GEE) model was used for data analysis. Authors state that the GEE model allows for interrelation among outcome measures on the same individual as occurs in crossover designs, and was the same model used to evaluate the effect of Na+ on blood pressure.

Authors reported an 85% power to detect 0.05 (two-sided) differences between the higher and lower concentrations of Na+ for outcomes of interest as follows:

Total cholesterol differences of 3% to 4%
TG differences of 12%
HDL/LDL ratio differences of 3%.

Data Collection Summary:

Timing of Measurements

Blood samples were drawn after a 12-hour fast at baseline (prior to the two-week run-in period) and during the final week of each 30-day period of defined diets.

Dependent Variables

Blood lipid values (total cholesterol, LDL, HDL and TGs) were all analyzed on a Hitachi 917 analyzer, except LDL, which was estimated by the Friedewald equation.

Independent Variables

Diet (control or study): Total energy intakes and intakes of key individual nutrients, which were calculated (total fat, types of fat and cholesterol, fiber, potassium, calcium, sodium, magnesium) from diet records.
Dietary sodium intake.

Control Variables

Body size (height and weight)
Physical activity level.

Description of Actual Data Sample:

Initial N

412 (56% women).

Attrition (Final N)

390 (triglyceride values only), but only 379 subjects reported LDL and triglyceride values
Analyses were performed with a N=390 where applicable (170 males, 220 females).

Age

Mean age = 48 to 49 years (±9.6 or 10.3 years in intervention and control group respectively).

Ethnicity

54% and 59% female subjects in the control and DASH groups respectively, with 59% African-American subjects in both groups.

Demographics

57% African American.

Anthropometrics

Mean BMI: 28.8 to 29.5
Mean diastolic blood pressures: 85.5 to 85.7
Mean systolic blood pressure: 134.0 to 135.5.

Location:

Multicenter trial, US.

Summary of Results:

Variables

Study Group

Mean and 95% CI

Control Group

Mean and 95% CI

Total cholesterol

(sodium effect)

0.01 (-0.07, 0.09)

P=0.8

0.05 (-0.03, 0.13)

P=0.12

HDL-Cholesterol

(sodium effect)

0.00 (-0.02, 0.03)

P=0.7

-0.02 (-0.04, 0.00)

P=0.10

LDL-Cholesterol

(sodium effect)

0.00 (-0.07, 0.08)

P=0.9

0.04 (-0.03, 0.11)

P=0.3

Triglyceride

(sodium effect)

0.03 (-0.04, 0.10)

P=0.4

0.06 (-0.01, 0.13)

P=0.07

TChol/HDL

(sodium effect)

-0.01 (-0.10, 0.08)

P=0.8

0.10 (0.00, 0.19)

P=0.04*

*Changing sodium levels between the higher and lower level and between the intermediate and lower levels resulted in a significant (P=0.04) increase in the total cholesterol-to-HDL ratio of 0.10, but authors remark that this change was not likely to be clinically relevant.

Author Conclusion:

Sodium intake at 50 to 150mmol per day had no effect on blood lipid concentrations.

Funding Source:

Government:

NIH, NHLBI

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?	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?	No
	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?	Yes
	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?	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?	N/A
	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)?	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?	N/A
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