EAL

NA: Dietary Factors and Effect on Sodium and Blood Pressure (2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine differences in dietary intake and blood pressure and their associations in four different ethnic Chinese populations, the Han, the Uygur, the Kazak and Tibetan subjects.

Inclusion Criteria:

Men and women aged 48 to 56 years.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment

This study used a sub-database of the Chinese sample of the WHO-Cardiovascular Disease and Alimentary Comparison (CARDIAC) Study
In each center, 100 men and 100 women were randomly selected from the population.

Design

Multicenter cross-sectional study.

Intervention

Participants invited to have a free physical exam and blood tests.

Statistical Analysis

Analysis of covariance method was used to estimate the adjusted mean values of BMI and other factors
Relative risks for hypertension posed by obesity and increased salt intake (assessed using elevated sodium excretion) were estimated using logistic regression models
Obesity and elevated sodium excretion were independent variables with adjustments for age, sex and potassium.

Data Collection Summary:

Timing of Measurements

Participants invited to free physical exam and blood tests.

Dependent Variables

Blood pressure measured using automated sphygmomanometer, average of three readings
24-hour urine samples for urinary sodium, potassium, magnesium, 3-methylhistidine and taurine excretion levels, urine sample collection lower in three ethnic groups (41.5% to 60.3%) than in the Han (79.3%)
Blood samples.

Independent Variables

Structured questionnaire used to collect data on demographic variables, medical history of hypertension and lifestyle
Obesity (defined as BMI over 26)
Elevated sodium excretion (over 244mmol per day).

Control Variables

Age
Sex
Potassium.

Description of Actual Data Sample:

Initial N: 775 Han (367 male, 408 female), 510 Uygur (264 male, 246 female), 204 Kazak (99 male, 105 female) and 125 Tibetan (52 male, 73 female) subjects
Attrition (final N): See above, total of 1,614 subjects (782 male, 832 female)
Age: 48 to 56 years
Ethnicity: Chinese
Anthropometrics: There were significant differences between the groups
Location: China.

Summary of Results:

24-Hour Urinary Excretion

	Han	Uygur	Kazak	Tibetan
BMI	21.9±0.1	23.6±0.3	25.9±0.4	20.7±0.4
Na (mmol/day)	193.0±3.5	173.5±6.0	213.1±9.6	253.7±10.2
K (mmol/day)	30.4±0.8	48.2±1.3	47.0±2.0	40.1±2.3
Na/K ratio	7.2±0.1	3.9±0.2	5.2±0.4	7.7±0.4
Mg (mg/day)	105.1±2.2	109.5±3.8	114.6±5.8	85.7±6.6

Other Findings

There were significant differences in mean BP and prevalence rates of hypertension, with both being higher in the Kazak and Tibetan subjects than in Han and Uygur subjects
The highest BMI was observed in the Kazak subjects, while the highest 24-hour urinary sodium and sodium to potassium ratio excretion were observed in the Tibetan subjects
There was a significant positive association between BMI and SBP and DBP in the Han, Uygur and Kazak subjects, but not Tibetan subjects
Increased sodium excretion or sodium-to-potassium ratios showed a significant positive association with SBP in Han, both SBP and DBP in Uygur and Tibetan, but not Kazak subjects
There were also significant differences in other factors, such as magnesium, 3-methylhistidine (3MH) and taurine excretion levels among the four ethnic peoples
In general, BMI, sodium or sodium-potassium ratios were positively and 3MH-creatinine and taurine-creatinine ratios were negatively associated with BP
After adjustment for age, sex and potassium, subjects with obesity (BMI over 26) had significantly higher relative risk of being hypertensive than those with BMI under 26 in the Han, Uygur and Kazak populations and subjects with elevated sodium excretion (sodium over 244mmol per day) had significantly higher relative risk of being hypertensive than those with sodium under 244mmol per day in the Han, Uygur and Tibetan populations
After adjustment for, age, sex and potassium, there was a significant negative association between magnesium excretion level and DBP in the Han subjects (R=-0.11, P<0.05) and in the Tibetan subjects (R=-0.21, P<0.05).

Author Conclusion:

In conclusion, the present study showed that the Kazak and Tibetan people had higher mean BP and prevalence of hypertension than the Han and Uygur people
These differences could be partly explained by the differences in several diet-related factors associated with cultural and environmental differences
Different health promotion strategies should thus be emphasized in different populations.

Funding Source:

University/Hospital:

Kyoto University (Japan), Chinese Academy of Medical Sciences (China), National Yang-Ming University (China),Tibet Institute of Medical Science (Tibet), Shanghai Institute of Hyperstension (China), Hebei Academy (China), University of East Asia (Japan), University of Tokyo

Reviewer Comments:

Excretion values of sodium, potassium and magnesium measured
Large sample sizes
Associations between groups not consistent, hard to draw conclusions
Did not control for alcohol consumption, physical activity or smoking
Urine samples not evenly distributed among groups.

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)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	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?		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?	N/A
	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?	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?	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?		No
	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?	No
	7.7.	Were the measurements conducted consistently across groups?	No
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