EAL

NA: Sodium or Sodium Chloride (2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the effects of an 18-month lifestyle modification intervention aimed at either weight loss or dietary sodium reduction on the incidence of hypertension during six to eight years of follow-up.

Inclusion Criteria:

Age between 30 and 54 years
Average DBP between 80mm and 89mm Hg
SBP under 160mm Hg.

Exclusion Criteria:

Evidence of hypertension or other cardiovascular disease
Extreme obesity (BMI over 36.1)
Heavy alcohol use (over 21 drinks per week).

Description of Study Protocol:

Recruitment: Men and women who had participated in the Trials of Hypertension Prevention, phase I
Design: Multi-center, randomized controlled trial
Blinding used: Measurements taken by blinded observers
Intervention: Subjects randomized to one of two 18-month lifestyle modification interventions aimed at either weight loss or dietary sodium restriction or a usual care control group.

Statistical Analysis

Baseline characteristics compared between intervention and control groups, using Student's T-tests for continuous variables and chi-square tests for categorical variables
Changes from baseline in weight, 24-hour urinary excretion of sodium, SBP and DBP, compared with use of Student's T-tests
Incidence of hypertension compared between intervention and control groups, with the use of chi-square tests
Logistic regression analysis used to compare risk of hypertension between intervention and control groups after adjustment for age, gender, baseline physical activity, alcohol consumption, education, weight, SBP and urinary excretion of sodium.

Data Collection Summary:

Timing of Measurements

Subjects randomized to 18-month interventions at baseline (1987-1988)
Baseline and follow-up data at three, six, 12 and 18 months
Measurements taken at post-trial follow-up (1994-1995).

Dependent Variables

Blood pressure measured using random-zero sphygmomanometer
Body weight
Urinary sodium and creatinine.

Independent Variables

Weight loss or sodium reduction intervention delivered by nutritionists and consisted of 90-minute group educational sessions, conducted weekly for the first 14 weeks of weight loss intervention and first 10 weeks for sodium reduction intervention, then held semi-monthly and monthly over 18 months' duration
Usual care control group.

Control Variables

Baseline age
Gender
Race
Physical activity
Alcohol consumption
Education
Body weight
SBP
Urinary sodium excretion.

Description of Actual Data Sample:

Initial N: 208 randomized into weight loss, sodium reduction or control groups

Attrition (Final N)

181 subjects (87.0%) participated in follow-up in 1994-1995

57% men

Among 27 non-respondents, one had died, one was seriously ill, 25 refused to participate.

Age

Subjects were 30 to 54 years old at baseline in 1987-1988.

Ethnicity

58% white.

Anthropometrics

There were no significant differences between groups at baseline.

Location

Baltimore, Maryland.

Summary of Results:

After 18 Months Active Control Active - Control P-Value

Weight Loss - Change in Weight (kg) -2.4±5.0 1.1±3.5 -3.5 <0.001

Weight Loss- Change in Na excretion (mmol/d)

-21.0±72.1

-26.3±67.5

-5.2
0.74

Weight Loss - Change in SBP (mm Hg) -6.9±6.4 -1.2±7.6 -5.8 <0.001

Weight Loss - Change in DBP (mm Hg) -8.6±4.7 -5.5±5.9 -3.2 0.005

Na Reduction - Change in weight (kg) 0.6±2.9 0.5±3.2 0.2 0.78

Na Reduction - Change in Na excretion (mmol/d) -53.5±63.3 -20.2±65.1 -33.3 0.008

Na Reduction - Change in SBP (mm Hg) -5.7±6.5 -2.4±8.5 -3.3 0.01

Na Reduction - Change in DBP (mm Hg)

-7.2±4.6

-5.6±5.9

-1.7
0.08

After Seven Years Active Control Active - Control P-Value

Weight Loss - Change in Weight (kg) 4.9±7.1 4.5±4.9 0.4 0.75

Weight Loss - Change in SBP (mm Hg) 2.0±12.4 3.7±13.4 -1.8 0.52

Weight Loss - Change in DBP (mm Hg) -6.5±7.5 -5.2±8.3 -1.3 0.42

Weight Loss - Use of antihypertensive medication (%) 13.2 28.6 -15.4 0.06

Na Reduction - Change in weight (kg) 10.8±61.0 0.3±75.0 10.4 0.41

Na Reduction - Change in SBP (mm Hg) -1.6±11.3 2.2±12.4 -3.8 0.08

Na Reduction - Change in DBP (mm Hg)
-7.5±7.5 -5.3±7.6 -2.3 0.097

Na Reduction - Use of antihypertensive medication (%) 19.0 24.3 -5.3 0.47

Other Findings

Body weight and urinary sodium were not significantly different among the groups at the post-trial follow-up

After seven years of follow-up, the incidence of hypertension was 18.9% in the weight-loss group and 40.5% in its control group. The incidence was 22.4% in the sodium reduction group and 32.9% in its control group.

Adjusted logistic regression analysis showed the odds of hypertension was reduced by 77% (odds ratio 0.23; 95% CI: 0.07 to 0.76, P=0.02) in the weight loss group and by 35% (odds ratio 0.65; 95% CI: 0.25 to 1.69, P=0.37) in the sodium reduction group, compared with their control groups.

Author Conclusion:

These results indicate that lifestyle modification such as weight loss may be effective in long-term primary prevention of hypertension

Our findings have important public health implications

Hypertension is a common and important modifiable risk factor for cardiovascular disease and total deaths

Lifestyle modifications such as weight loss and sodium reduction should be recommended as a principal component of strategies to prevent hypertension and its complications in the US general population.

Funding Source:

Government: NHLBI, NIH

Not-for-profit

0

Foundation associated with industry:

Reviewer Comments:

87% follow-up after seven years

Authors note that mechanisms for long-term benefit are uncertain.

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? N/A

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? ???

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)? 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? 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

After 18 Months	Active	Control	Active - Control	P-Value
Weight Loss - Change in Weight (kg)	-2.4±5.0	1.1±3.5	-3.5	<0.001
Weight Loss- Change in Na excretion (mmol/d)	-21.0±72.1	-26.3±67.5	-5.2	0.74
Weight Loss - Change in SBP (mm Hg)	-6.9±6.4	-1.2±7.6	-5.8	<0.001
Weight Loss - Change in DBP (mm Hg)	-8.6±4.7	-5.5±5.9	-3.2	0.005
Na Reduction - Change in weight (kg)	0.6±2.9	0.5±3.2	0.2	0.78
Na Reduction - Change in Na excretion (mmol/d)	-53.5±63.3	-20.2±65.1	-33.3	0.008
Na Reduction - Change in SBP (mm Hg)	-5.7±6.5	-2.4±8.5	-3.3	0.01
Na Reduction - Change in DBP (mm Hg)	-7.2±4.6	-5.6±5.9	-1.7	0.08

After Seven Years	Active	Control	Active - Control	P-Value
Weight Loss - Change in Weight (kg)	4.9±7.1	4.5±4.9	0.4	0.75
Weight Loss - Change in SBP (mm Hg)	2.0±12.4	3.7±13.4	-1.8	0.52
Weight Loss - Change in DBP (mm Hg)	-6.5±7.5	-5.2±8.3	-1.3	0.42
Weight Loss - Use of antihypertensive medication (%)	13.2	28.6	-15.4	0.06
Na Reduction - Change in weight (kg)	10.8±61.0	0.3±75.0	10.4	0.41
Na Reduction - Change in SBP (mm Hg)	-1.6±11.3	2.2±12.4	-3.8	0.08
Na Reduction - Change in DBP (mm Hg)	-7.5±7.5	-5.3±7.6	-2.3	0.097
Na Reduction - Use of antihypertensive medication (%)	19.0	24.3	-5.3	0.47

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?	N/A
	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?	???
	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)?	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?	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