The Effect of a Reduction in Sodium Intake on Blood Pressure asModified by the Control Group's Sodium Level: A Meta-analysis Open Access

Abstract

Background: The link between sodium reduction and decreased blood pressure (BP) has been established through previous studies and meta-analyses. However, the link between usual sodium intake level and its effect on BP has not been investigated.

Objectives: To assess whether the sodium to blood pressure association is different according to initial level of sodium intake and BP status.

Search methods: The Cochrane Central Register of Controlled Trials (January 2005 to August 2011), MEDLINE (January 2005 to June 2011), EMBASE (January 2005 to June 2011), WHO ICTRP, LILACS, and reference lists of articles were searched.

Selection criteria: Randomized controlled trials which allocated at least one group of participants to reduced sodium intake and one to regular sodium intake for a minimum of four weeks and reported results on BP.

Data collection and analysis: Two authors independently assessed trial quality, extracted data, and entered it into the Cochrane Collaboration Review Manager 5.1. Study authors were contacted to obtain missing information.

Main results: Thirty-six studies with 3304 participants in the reduced sodium group and 3432 in the usual sodium group were included in the meta-analysis. The pooled estimates for changes in BP using a random effects model were -3.39 mmHg (95% CI: -4.31, -2.46) [systolic] and -1.55 mmHg (95% CI: -2.11, -0.98) [diastolic]. When studies were divided into quartiles based on the level of sodium intake in the control group (lowest sodium intake in the first quartile and highest sodium intake in the fourth quartile), no statistically significant relationship was found between the control group's sodium intake level and blood pressure reduction. When stratified status, a larger decrease in BP was noted in hypertensives compared to the normotensives. There were no observable patterns when the groups were divided by study design. Sensitivity analysis where three low quality studies were removed showed no difference in the overall estimate.

Authors' conclusions: This meta-analysis of randomized controlled trials illustrates that individuals at both higher and lower initial sodium intake levels benefit in terms of BP reduction when sodium intake is decreased and that those with hypertensive BP status benefit more than normotensives.

Table of Contents

Introduction ..................................................................................................................................................... 1

Methods ........................................................................................................................................................... 5

Results ........................................................................................................................................................... 19

Figure 1: PRISMA Diagram ..................................................................................................................... 21

Table 1: Characteristics of Included Studies ............................................................................................. 23

Table 2: Overall Pooled Estimates of Changes in Blood Pressure Using the Random Effects Model ..... 37

Table 3: Characteristics of Studies by Type of Study Design ................................................................... 38

Table 4: Overall Pooled Estimates of Changes in Blood Pressure by Study Design ................................ 38

Table 5: Characteristics of Studies by Participants' Blood Pressure Status .............................................. 39

Table 6: Overall Pooled Estimates of Changes in Blood Pressure by Participants' Blood Pressure Status40

Discussion ..................................................................................................................................................... 42

Table 7: Risk of Biases Among Studies Included in the Meta-Analysis ................................................... 46

Appendix A: Search Strategy ........................................................................................................................ 50

Appendix B: Data Extraction Form Template ............................................................................................... 52

Appendix C: Characteristics of Excluded Studies ......................................................................................... 57

Appendix D: Characteristics of Studies Awaiting Classification .................................................................. 58

Appendix E: Characteristics of Ongoing Studies .......................................................................................... 59

Appendix F: References to Included Studies ................................................................................................ 60

Appendix G: References to Excluded Studies ............................................................................................... 64

Appendix H: References to Studies Awaiting Classification ........................................................................ 66

Appendix I: References to Ongoing Studies ................................................................................................. 67

Appendix J: Risk of Bias Graph .................................................................................................................... 68

Appendix K: Risk of Bias Summary ............................................................................................................. 69

Appendix L: Forest Plot of Changes in Systolic Blood Pressure Using the Random Effects Model ............ 70

Appendix M: Forest Plot of Changes in Diastolic Blood Pressure Using the Random Effects Model ......... 71

Appendix N: Division of Cohorts into Quartiles for Overall Analysis ......................................................... 72

Appendix O: Funnel Plot - Systolic Blood Pressure ..................................................................................... 73

Appendix P: Funnel Plot - Diastolic Blood Pressure ..................................................................................... 74

References ..................................................................................................................................................... 75

About this Master's Thesis

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School	Rollins School of Public Health
Department	Hubert Department of Global Health
Degree	MS
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health
Keyword	blood pressure sodium
Committee Chair / Thesis Advisor	Ali, Mohammed, Emory University
Committee Members	Aburto, Nancy Jennings, Emory University

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