EAL

NA: Effect on Blood Pressure (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine if elevated sodium and nitrate levels in drinking water affects blood pressure in schoolchildren.

Inclusion Criteria:

Fourth and fifth graders
Residing in one of three regions:
- Israeli coastal plain area
- Central Golan Heights
- Southern Golan Heights.
No history of parental hypertension
Pre-pubertal children of Tanner stages zero to one (sex maturity rating).

Exclusion Criteria:

Undisclosed.

Description of Study Protocol:

Recruitment: Fourth and fifth graders matched for age, weight and height were assembled from the Israeli coastal plain area, central Golan Heights, or the southern Golan Heights
Design: Participants were assembled into three groups:
- Group One: Consisted of 452 children residing in the Israeli coastal plain area with high sodium and high nitrate levels in the drinking water
- Group Two: Had 418 children from the central Golan Heights with low sodium and high nitrate levels in the drinking water
- Group Three: Had 86 children from the southern Golan Heights with low sodium and low nitrate levels in the drinking water.
Intervention: Sodium and nitrate levels in the drinking water
- Group One: 196 and 49mg per L, respectively
- Group Two: 25 and 40mg per L, respectively
- Group Three: 35 and 15mg per L, respectively.

Data Collection Summary:

Timing of Measurements

Urine sample to measure sodium-to-creatinine ratio
Systolic blood pressure, diastolic blood pressure, heart rate and mean arterial blood pressure.

Dependent Variables

Systolic blood pressure, diastolic blood pressure, mean arterial blood pressure, heart rate and urinary sodium/creatinine levels.

Independent Variables

Sodium and nitrate levels in drinking water.

Component	Group One	Group Two	Group Three
Sodium (mg per day)	196	25	35
Nitrate (mg per L)	49	40	15

Description of Actual Data Sample:

Initial N: N=956
Attrition (final N): N=956
Age:
- Group One: 10.6±1.2
- Group Two: 10.5±1.2
- Group Three: 10.8±1.1.
Ethnicity: Undisclosed
Other relevant demographics: All children resided in Israel.

Anthropometrics

Group	N	Age (Years)	Weight (kg)	Height (cm)	Sodium (mg/L)	Nitrates (mg/:)
One	452	10.6±1.2	35.6±7.6	143±9.2	196	49
Two	418	10.5±1.2	34.9±8.6	141.7±9.5	25	40
Three	86	10.8±1.1	33.6±7.2	141.2±9.1	35	15

Location

Israel.

Summary of Results:

Group	HR Beats per Minute	SBP mm Hg	DBP mm Hg	MAP mm Hg	UNa/Cr
One	91±13	116±12	66±7	86±9	2.9±0.5
Two	85±13	111±11*	66±6	83±8***	1.1±0.7***
Three	88±10	107±8**	63±8	81±7***	1.2±0.3***

*P<0.05 vs. Group One
**P<0.05 vs. Groups One and Two
***P<0.05 vs. Group One.

Author Conclusion:

Drinking water containing a high concentration of sodium and nitrate leads to an increase of blood pressure (at least SBP and MAP) in fourth and fifth graders. The influence of sodium and nitrate appears to be independent of each other while at the same time being additive. Further long-term studies are needed to ascertain whether these effects are sustained or aggravated through adult life.

Funding Source:

Reviewer Comments:

Chloride which was not studied could have played a role in the studies results
Lack of high-sodium, low-nitrate group
The determination of sodium intake from just one urine sample has the potential of being an inaccurate estimate.

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?		???
	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?	???
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	No
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
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)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	???
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	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?		N/A
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	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?		N/A
	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.)	N/A
	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?	N/A
	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?	N/A
	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?	No
	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?	N/A
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	???
	7.5.	Was the measurement of effect at an appropriate level of precision?	???
	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?		???
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	???
	8.2.	Were correct statistical tests used and assumptions of test not violated?	???
	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)?	???
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	???
	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?		???
	10.1.	Were sources of funding and investigators' affiliations described?	No
	10.2.	Was the study free from apparent conflict of interest?	???