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Advice to reduce dietary salt for prevention of cardiovascular disease

  1. Lee Hooper1,*,
  2. Christopher Bartlett2,
  3. George Davey Smith3,
  4. Shah Ebrahim4

Editorial Group: Cochrane Hypertension Group

Published Online: 26 JAN 2004

Assessed as up-to-date: 25 NOV 2003

DOI: 10.1002/14651858.CD003656.pub2


How to Cite

Hooper L, Bartlett C, Davey Smith G, Ebrahim S. Advice to reduce dietary salt for prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2004, Issue 1. Art. No.: CD003656. DOI: 10.1002/14651858.CD003656.pub2.

Author Information

  1. 1

    University of East Anglia, School of Medicine, Health Policy & Practice, Norwich, UK

  2. 2

    North Swindon District Centre, Swindon Primary Care Trust, Swindon, Wiltshire, UK

  3. 3

    University of Bristol, Department of Social Medicine, Bristol, UK

  4. 4

    London School of Hygiene & Tropical Medicine, Department of Epidemiology & Population Health, London, UK

*Lee Hooper, School of Medicine, Health Policy & Practice, University of East Anglia, Norwich, NR4 7TJ, UK. l.hooper@uea.ac.uk.

Publication History

  1. Publication Status: Edited (no change to conclusions)
  2. Published Online: 26 JAN 2004

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Characteristics of included studies [ordered by study ID]
Alli 1992

MethodsRCT: GPs were 'selected at random' (GPs were randomised, not participants, 9 gave dietary advice and 10 did not).


ParticipantsUntreated hypertensives, Italy, mean age 48 years, 42% male, ?% white, BMI<30.
Inclusion criteria: DBP 90-104 mmHg over 6 weeks, not on AHTM.


InterventionsLS: received low sodium dietary advice (individual counselling by GP, reinforced at each clinic visit. Main messages (leaflet) don't add salt at table or in cooking, restrict salty processed foods, eat more fresh/ frozen foods and seasoning advice), USE Target: <=80,
C maintained usual diet


OutcomesBP & USE at 1,3,6, 9 & 12 mo


NotesPB: no.
OAB: no
AL: Losses excluded.
Assigned: LS 40, C 37
Follow up: LS 26, C 30 (12 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?NoC - Inadequate

Arroll 1995

MethodsRCT: 'factorial type RCT design'.


ParticipantsTreated hypertensives, New Zealand, mean age 55 years, 52% male, ?% white.
Inclusion criteria: AHTM treated hypertension (DBP >70 to 105 mmHg or SBP >155 to 180 mmHg).


InterventionsLS: on medication, asked to reduce use of high salt foods, salt added at table and in cooking (led by whom?, group or individual?). Each given an article on BP and salt restriction, a leaflet and a book with the Na content of common foods , USE Target: Not specified,
C: on medication, no intervention


OutcomesBP & AHTM levels following withdrawal of AHTM at 0 and 6 mo, USE at 6 mo


NotesPB: no
OAB: yes
AL: Losses excluded from BP measurement. No adjustment made for those who decreased or stopped medication
Assigned: LS 51, C 49
Follow up: LS 44, C 43 (6 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

Costa 1981

MethodsRCT: 'randomly divided into 2 groups'.


ParticipantsUntreated hypertensives, Italy, age range 16-31 years, ?% male, ?% white.
Inclusion criteria: untreated borderline hypertension


InterventionsLS: given a low salt diet (no data on who gave advice, group or individual counselling, materials used, or main messages), Target: 3 g NaCl/day,
C: advised on diet with free salt intake


OutcomesBP & intra-lymphocytic sodium at 0 & 12 mo


NotesPB: no.
OAB: unclear.
AL: Not specified.
Assigned: LS 21, C 20
Follow up: LS 20, C 21 (sic)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

HPT

MethodsRCT: randomisation code 'centrally generated by computer'.


ParticipantsNormotensives, USA, mean age 39 years, 62% male, 84% white.
Inclusion criteria: high normotensive, DBP 78-89, not on AHTM


InterventionsLS: on dietary and behavioural change programme (led by personnel trained and experienced in effecting behaviour change related to food, group sessions with individual counselling if sessions missed, newsletter between sessions, self assessment, goal setting, participant manual, food counter, cookbook, food demonstrations and tasting, team building exercises, tokens of accomplishment), USE Target: </=70,
C: no dietary counselling


OutcomesBP & USE at 0, 6, & 36 mo, % on anti-hypertensive medication


NotesPB: no
OAB: yes
AL: Participants with no follow-ups excluded; others given reading from last visit (or treated BP if higher).
Assigned: LS 196, C 196
Follow up: LS 174, C 191 (6 mo), LS 175, C 178 (36 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?YesA - Adequate

Morgan 1978

MethodsRCT: 'were divided randomly into 4 subgroups'.


ParticipantsUntreated hypertensives, Australia, >50 years, 100% male, ethnicity not stated.
Inclusion criteria: borderline hypertension, no AHTM (DBP 95-109 mmHg as a mean of 2 or 4 readings)


InterventionsLS: instructed to reduce their dietary sodium chloride intake, advice repeated at 3 months (no data on who gave advice, group or individual counselling, materials used, or main messages), DSI Target: 70-100,
C: no dietary treatment, reviewed 6 monthly as LS group


OutcomesBP & USE at 0, 6, 12, 18, 24 mo


NotesPB: no.
OAB: yes
AL: Those with no follow-up excluded. Reading at last visit used for remainder.
Assigned: LS 34, C 33 for BP (LS 35, C 42 for mortality)
Follow up: LS 26, C 21 (24 mo) (all followed re mortality)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

Morgan 1987

MethodsRCT: 'randomised in blocks of 4'


ParticipantsTreated hypertensives, Australia, mean age 61 years, 100% male, ?% white.
Inclusion criteria: hypertension (DBP <85 mmHg) while on AHTM (DBP >100 uncontrolled).


InterventionsLS: withdrawal of AHTM after 3 months on low sodium diet (led by whom?, no details of programme), DSI Target: 50-75,
C: withdrawal of anti-hypertensives after 3 months, maintained normal diet


OutcomesNecessity to restart AHTM following withdrawal, USE at 0 & 9 mo


NotesPB: no.
OAB: yes
AL: Last BP reading before reinstatement was used; all had at least one follow-up.
Assigned: LS 10, C 10
Follow up: LS 10, C 10 (9 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

Silman 1983

MethodsRCT: 'randomisation after stratification by practice'.


ParticipantsUntreated hypertensives, UK, aged 50 to 64, ?% male, ?% white.
Inclusion criteria: hypertension (DBP 95 - 104 mmHg over one year).


InterventionsLS: general health education group package with spouses (eating sensibly, stopping smoking, regular exercise, stress avoidance) plus taught diet (diet sheet given) lead by researcher, USE Target: 100,
C: general health education group package only


OutcomesBP & USE at 0, 1, 2, 3, 6 & 12 mo


NotesPB: no,
OAB: unclear.
AL: Losses excluded. Baseline readings for "excluded" compared with those for "included".
Assigned: LS 12, C 16
Follow up: LS 10, C 15 (12 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

Thaler men 1982

MethodsRCT: index subjects were subdivided into two groups in such a way that the following factors were kept balanced: sex, decade of age, SBP, AHTM, number of index persons per family, number of other persons in family. The two groups were randomly assigned to control and salt restriction respectively'.


ParticipantsUntreated hypertensives, New Zealand, mean age 41 years, 48% male, ethnicity not stated.
Inclusion criteria: For index subjects, SBP 137-180 mmHg, some (21%) on AHTM. Family members also included.


InterventionsLS: salt restriction programme for the whole family (led by a nutritionist, gradually introduced, individual counselling, some at the family home, main messages to stop adding salt, cut out salt in cooking and restrict high sodium foods, low sodium baking powder and baking soda were provided and a local baker made low sodium bread, cookbook provided), USE Target: not stated,
C: asked to eat usual diet


OutcomesUSE at 0 & 8 mo


NotesPB: no.
OAB: unclear.
AL: losses excluded.
Assigned: LS 80 (38 index + 42 family), C 84 (39 index + 45 family) .
Follow up: LS 69 (37 index, 19 men & 18 women), C 67 (35 index, 17 men & 18 women) (8 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

Thaler women 1982

Methodsas Thaler men


Participantsas Thaler men


Interventionsas Thaler men


Outcomesas Thaler men


Notesas Thaler men


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?UnclearB - Unclear

TOHP phase I

MethodsRCT: 'randomisation assignments were obtained from the co-ordinating center by telephone... when telephone contact not possible sealed opaque envelopes were used'.


ParticipantsNormotensives, USA, mean age 43 years, 71% male, 77% white.
Inclusion criteria: High normal (DBP 80 to 89 mmHg over 9 readings), not on AHTM.


InterventionsRegimen: LS group nutrition and behavioural counselling programme (led by nutritionists, including food tasting and samples, problem solving exercises, shopping lists and guides, peer support and family involvement, field trips to shops and restaurants, motivational activities, food diaries and self assessment of sodium intake), USE Target: 80,
C: no intervention


OutcomesBP & USE at 0, 6, 12 & 18 mo


NotesPB: no
OAB: yes
AL: Participants with no follow-up reading taken as zero change; others given reading from last visit.
Assigned: LS 327, C 417
Follow up: LS 301, C 392 (12 mo),
LS 304, C 395 (18 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?YesA - Adequate

TOHP phase II

MethodsRCT: by telephone to TOHP co-ordinating center or sealed, opaque envelope.


ParticipantsNormotensives, USA, mean age 44 years, 67% male, 81% white.
Inclusion criteria: High normal (DBP 83 to 89 mmHg, SBP<=140 mmHg), not on AHTM. (People unwilling to comply with intervention excluded.)


InterventionsLS: dietary and behavioural change programme (led by dietitians, psychologists and health counselors, programme as TOHP I with individual counselling as well as group sessions) intensive early on, contact maintained later, USE Target: 70,
C: no active intervention


OutcomesBP & USE at 0, 6, 18 & 36 mo (42 or 48 mo sometimes)


NotesPB: no.
OAB: yes
AL: Those with no follow-up reading given random value from range of results; others given reading from last visit.
Assigned: LS 594, C 596
Follow up: LS 529, C 538 (6 mo), LS 515, C 514 (36 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?YesA - Adequate

TONE

MethodsRCT: 'using a computer program each participants elegibility was confirmed prior to enrollment in the trial, randomisation was stratified by clinic and weight status'.


ParticipantsTreated hypertensives, USA, mean age 67 years, 49% male, 76% white.
Inclusion criteria: AHTM-treated HT (DBP <85 mmHg, SBP <145 mmHg).


InterventionsLS: attempted withdrawal of AHTM, group plus individual nutrition and behavioural counselling programme (led by nutritionists), USE Target: <80,
C: attempted withdrawal of anti-hypertensives, no counselling but invited to meetings on unrelated topics


OutcomesCombined BP, use of AHTM & CV events. USE at 0, 9, 18 & 30 mo


NotesPB: no.
OAB: yes
AL: Used survival analysis with censoring to project proportions free of endpoints.
Assigned: LS 340, C 341
Follow up: LS 310, C 314 (30 mo)


Risk of bias

ItemAuthors' judgementDescription

Allocation concealment?YesA - Adequate

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Aberg 1989Multifactorial management programme (dietary changes, stress management and increased physical activity)

Ambard 1904Not randomised.

Ambrosioni 1982Less than 6 months follow up from initial intervention

Anderson 1990Less than 6 months follow up from initial intervention

Berglund 1989Multifactorial management programme, less than 6 months follow up from initial intervention

Bompiani 1988Less than 6 months follow up from initial intervention

Cappuccio 1997Less than 6 months follow up from initial intervention

Carney 1975Not randomised.

Corcoran 1951Not randomised.

Dahl 1958Not randomised.

DASHLess than 6 months follow up from initial intervention

DISHMultifactorial, reduces sodium intake, but also increases potassium intake

Dole 1951Not randomised.

Dubbert 1995Less than 6 months follow up from initial intervention

Erwteman 1984Less than 6 months follow up from initial intervention

Evers 1987Multifactorial management programme

Fagerberg 1984Less than 6 months follow up from initial intervention

Geleijnse 1995Multifactorial, reduces sodium intake, but also increases potassium intake

Gillum 1983Less than 6 months follow up from initial intervention, no control group

Grimm 1990All on salt restriction, no 'usual diet' control

HCPMultifactorial management programme, reduction of sodium with weight loss and alcohol reduction

Henningsen 1980Less than 6 months follow up from initial intervention (follow up between 4 and 8 months of intervention) - suggests that later results will be published but none found and contact not established with the author

Holly 1981Less than 6 months follow up from initial intervention

Iwaoka 1994Less than 6 months follow up from initial intervention

Jula 1990Multifactorial management programme (sodium reduction with fat reduction)

Jula 1992aMultifactorial management programme (sodium reduction with weight and fat reduction)

Jula 1992bMultifactorial management programme (sodium reduction with weight and fat reduction)

Jula 1994Multifactorial management programme (sodium reduction with weight and fat reduction)

Koopman 1990The randomised part of the study only lasted 3 months, multifactorial intervention

Korhonen 1999Less than 6 months follow up from initial intervention

Logan 1986Compares an intensive intervention with a less intensive intervention to restrict sodium intake, but no 'usual diet' control group used. (This is a randomised clinical trial lasting 6 months).

MacGregor 1982aNot randomised.

MacGregor 1982bLess than 6 months follow up from initial intervention

MacGregor 1989All on salt restriction, no 'usual diet' control

Magnani 1976No 'usual diet' control

McDonald 1988Multifactorial management programme (sodium reduction with weight and alcohol reduction)

Morgan 1988Less than 6 months follow up from initial intervention

Muhlhauser 1993Multifactorial management programme

Myers 1989Less than 6 months follow up from initial intervention

Nestel 1993Less than 6 months follow up from initial intervention

Neyses 1985Children included

Nicholson 1986Less than 6 months follow up from initial intervention

Nicholson 1987Less than 6 months follow up from initial intervention

Nowson 1988Less than 6 months follow up from initial intervention

Nugent 1984Comparison of two different methods of salt restriction, no 'usual diet' control

ODESMultifactorial management programme

Omvik 1986All on salt restriction, no 'usual diet' control

Omvik 1995All on salt restriction, no 'usual diet' control

Parijs 1973Not randomised.

Perera 1947Not randomised.

Priddle 1962Not randomised.

Rissanen 1985No 'usual diet' controls

Roca-Cusachs 1991Multifactorial management programme, reduces sodium and also reduces weight, fat and alcohol.

Sagnella 1987Less than 6 months follow up from initial intervention

Shibata 1979Not randomised.

Singer 1984Less than 6 months follow up from initial intervention

Singer 1995Less than 6 months follow up from initial intervention

Stamler 1989Multifactorial management programme, reduces sodium as well as weight and alcohol with increased exercise

TAIMMultifactorial, reduces sodium intake, but also increases potassium intake

TOMHSAll on salt restriction, no 'usual diet' control

Velloso 1991Less than 6 months follow up from initial intervention

Watt 1983Less than 6 months follow up from initial intervention

Watt 1986Less than 6 months follow up from initial intervention

Weinberger 1988All on salt restriction, no 'usual diet' control. Less than 6 months follow up from initial intervention.

Wing 1984Less than 6 months follow up from initial intervention

Zoccali 1993Less than 6 months follow up from initial intervention

 
Comparison 1. Mortality and cardiovascular morbidity

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Mortality42393Risk Ratio (M-H, Random, 95% CI)0.90 [0.36, 2.24]

 2 Cardiovascular morbidity2748Risk Ratio (M-H, Random, 95% CI)0.82 [0.56, 1.21]

 
Comparison 2. Systolic blood pressure

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Trials with 6 to 12 months of follow up72303Mean Difference (IV, Random, 95% CI)-2.51 [-3.82, -1.21]

    1.1 Normotensives
32124Mean Difference (IV, Random, 95% CI)-2.31 [-3.06, -1.55]

    1.2 Hypertensives
4179Mean Difference (IV, Random, 95% CI)-8.01 [-15.78, -0.24]

 2 Trials with 13 to 60 months of follow up42347Mean Difference (IV, Random, 95% CI)-1.12 [-1.83, -0.41]

    2.1 Normotensives
32285Mean Difference (IV, Random, 95% CI)-1.09 [-1.92, -0.26]

    2.2 Hypertensives
162Mean Difference (IV, Random, 95% CI)-1.50 [-12.60, 9.60]

 3 Trials with more than 60 months of follow up1128Mean Difference (IV, Random, 95% CI)-3.80 [-7.91, 0.31]

    3.1 Normotensives
1128Mean Difference (IV, Random, 95% CI)-3.80 [-7.91, 0.31]

   3.2 Hypertensives
00Mean Difference (IV, Random, 95% CI)Not estimable

 
Comparison 3. Diastolic blood pressure

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Trials with 6 to 12 months of follow up52211Mean Difference (IV, Random, 95% CI)-1.21 [-1.84, -0.59]

    1.1 Normotensives
32124Mean Difference (IV, Random, 95% CI)-1.16 [-1.77, -0.56]

    1.2 Hypertensives
287Mean Difference (IV, Random, 95% CI)-4.65 [-9.33, 0.04]

 2 Trials with 13 to 60 months of follow up42347Mean Difference (IV, Random, 95% CI)-0.62 [-1.54, 0.31]

    2.1 Normotensives
32285Mean Difference (IV, Random, 95% CI)-0.52 [-1.05, 0.01]

    2.2 Hypertensives
162Mean Difference (IV, Random, 95% CI)-7.0 [-12.53, -1.47]

 3 Trials with more than 60 months of follow up1128Mean Difference (IV, Random, 95% CI)-2.2 [-4.83, 0.43]

    3.1 Normotensives
1128Mean Difference (IV, Random, 95% CI)-2.2 [-4.83, 0.43]

   3.2 Hypertensives
00Mean Difference (IV, Random, 95% CI)Not estimable

 
Comparison 4. Urinary sodium excretion

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Urinary sodium excretion at different times following intervention7Mean Difference (IV, Random, 95% CI)Subtotals only

    1.1 6-12 months following initiation of intervention
72166Mean Difference (IV, Random, 95% CI)-48.94 [-65.42, -32.46]

    1.2 13 to 60 months following initiation of intervention
42787Mean Difference (IV, Random, 95% CI)-35.53 [-47.22, -23.85]

    1.3 More than 60 months following initiation of intervention
1120Mean Difference (IV, Random, 95% CI)10.5 [-13.83, 34.83]

 
Comparison 5. Dropouts

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Comparison of dropouts at longest follow up103463Risk Ratio (M-H, Random, 95% CI)1.04 [0.86, 1.25]

 
Table 1. Data - total deaths and cardiovascular events (including cardiovascular deaths)

TrialDeaths, CDeaths, LSCV events, CCV events, LS

TOHP phase I1 (pancreatic cancer)0

TOHP phase II2 (causes not specified)3 (causes not specified)

HPT1 (no cause specified)1 (no cause specified)'no differences among the treatment groups in gross morbidity, as indicated by periods of hospitalization, or in deaths'

Morgan 19785 (causes of death: 1 arthritis, 1 congestive cardiac failure, 1 cerebrovascular accident, 1 pulmonary oedema and 1 unknown)4 (causes of death: 1 cerebrovascular accident bronchospasm, 1 myocardial infarction, 1 congestive cardiac failure, 1 cardiorespiratory failure)During first 2 years of study 3 were treated for congestive cardiac failure and 0 died of CV causes, 2 died from CV causes during the next 3 years.During the first 2 years of study 2 were treated for congestive cardiac failure and 1 person died (of CVA bronchiospasm), 3 died from CV causes during the next 3 years.

TONE46 people (2 stroke, 7 TIA, 4 MI, 17 angina, 1 congestive heart failure, 3 arrhythmia and 19 other cardiovascular (further 21 CV events (no. of people unclear) in the weight loss only group))36 people (1 stroke, 7 TIA, 2 MI, 9 angina, 2 congestive heart failure, 6 arrhythmia and 12 other cardiovascular (further 23 CV events (no. of people unclear) in the combined low sodium and weight loss group))

Alli 1992(1 case of ischaemic heart disease in the dropouts, but not clear from controls or low salt, or whether fatal)

Total986250

 
Table 2. Data - BP & urinary sodium ('mean (sd)' for control / 'mean (sd)' for low salt)

Trial nameinitial SBP, mmHgSBP ch, 6-12 moSBP ch, 13-60 moinitial DBP, mmHgDBP ch, 6-12moDBP ch, 13-60moinitial urinary NaNa ch, 6-12moNa ch, 13-60mo

HPT123.9 /124.06 months:-2.1 (8.3) / -3.8 (7.9) (adjusted)36 months: -2.9 (9.3) / -2.8 (9.2) (adjusted)83.0 /82.66 months: -3.0 (6.9) /-3.4 (6.6) (adjusted)36 months: -3.0 (6.7) / -2.8 (6.6) (adjusted)164.9 /162.6 (corrected from 8 hour overnight urine samples)6 months:-14.8 (67.2) / -35.7 (63.5) (corrected from 8 hour overnight urine samples)36 months: 0.0 (71.1) / -16.0 (68.0) (corrected from 8 hour overnight urine samples)

TOHP phase I125.1 (8.1) / 124.8 (8.5)12 months:-3.9 (7.4) / -5.8 (7.5)18 months: -3.16 (8.1) / -4.9 (7.8)83.9 (2.8) /83.7 (2.7)12 months:-3.4 (5.7) / -4.4 (5.4)18 months: -3.3 (5.7) / -4.1 (5.7)156.4 (60.5)/ 154.6 (59.9)6 months:+2.8 (80.3) / -55.7 (76.1)18 months: -11.3 (77.7) / -55.2 (76.9)

TOHP phase II127.3 (6.4) /127.7 (6.6)6 months:-2.2 (8.1) /-5.1 (8.6)36 months:+0.3 (8.9) /-0.7 (9.2)85.8 (1.9) /86.1 (1.9)6 months:-2.8 (6.1) /-4.4 (6.7)36 months: -2.4 (7.1) / -2.9 (6.8)188.0 (80.9) /186.1 (80.7)6 months: -27.6 (108.0) / -78.0 (86.2)36 months: -10.5 (88.5) / -50.9 (86.3)

Morgan 1978165 (16.7) /160 (22.3)12 months:-3 (22.3) /-3(22.3)24 months:-4 (22.3) /-5.5 (22.3)97 (8.6) /97 (8.7)12 months: +1 (11.1) /-3 (11.1)24 months: +2 (11.1) / -5 (11.1)191 (35) /195 (55.0)Not given24 months: -11 / -38

Costa 1981143.4 (13) /143.3 (15)12 months:4.3 (18.8) /-14.0 (18.5) (sd imputed)84.1 (7) /84.2 (9)12 months: -0.2 (32.6) /-6.1 (31.7) (calculated sd)Not givenNot given

Thaler 1982, index men139 (12) / 137 (14)12 months:+3.4 (17.4) / -5.0 (8.3) (levels of medication altered in some participants through trial)90 (12) /86 (9)12 months:+0.8 (9.2) /+0.6 (9.2) (levels of medication altered in some participants through trial)159.5 (72.5) / 178.1 (76.5)12 months:+49.3 (67.7) / -64.9 (97.9)

Thaler 1982, index women148 (25) /145 (18)12 months:+1.1 (14.4) /-11.1 (24.2) (levels of medication altered in some participants through trial)83 (12) /86 (11)12 months:+2.8 (8.5) /-6.8 (11.9) (levels of medication altered in some participants through trial)120.1 (41.5) /118.0 (39.9)12 months:+8.4 (63.0) / -31.6 (55.1)

Silman 1983160.5 /165.312 months:-20.0 (24.0) /-28.7 (26.6)98.3 /98.812 months: -11.4 (10.5) /-17.7 (11.4)146.5 /150.812 months:26.4 (39.8) / -26.4 (30.2)

Alli 1992148.3 (10.6) / 150.8 (8.7)12 months:-0.3 (16.4) /-6.6 (13.6) (sd imputed)97.2 (3.8) /97.0 (3.1)12 months: -2.7 (16.6) / -6.4 (18.5) (sd calculated)177.3 (61.7) /177.3 (61.0)12 months:-4.2 /+8.6 (data measured off graph)

Morgan 1987143 (15.8) /143 (15.8)9 months:+35 (25.7)/+12 (21.5) (sd imputed, levels of medication altered in some participants through trial)81 (6.3) /83 (6.3)9 months:+17 (28.7) /+7 (22.2) (sd calculated, levels of medication altered in some participants through trial)163 (50.6) /168 (37.9)-8 / -93

Arroll 1995145.3 (15.7) /145.4 (15.9)6 months:-6.2 (21.0) /-9.1 (21.7) (sd imputed, levels of medication altered in some participants through trial)94.0 (9.8) /86.4 (9.9)6 months: -4.8 (36.1) / -1.7 (34.9) (sd calculated, levels of medication altered in some participants through trial)Not givenNot given

TONE128 (9) / 129 (9)Not given71 (7) /72 (7)Not given146.2 / 145.39 months: +1.4 (132) / -45.2 (132) (data include those in weight loss group with control, and weight loss plus sodium reduction with intervention)30 months:-0.3 (132) /-39.8 (143) (data include those in weight loss group with control, and weight loss plus sodium reduction with intervention)


 
Table 3. Meta-analysis, sugrouping and sensitivity analysis results

OutcomeTimeType of analysisDescriptionNumber of studiesWMD95% CIp for heterogeneity

Systolic blood pressure (mmHg)6 to 12 monthsOverall meta-analysis7-2.5-3.8 to -1.20.08

Systolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisDrop imputed standard deviations5-2.3-3.0 to -1.70.57

Systolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisSmallest calculated standard deviations7-3.1-4.8 to -1.3<0.01

Systolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisAllocation concealment3-2.3-3.1 to -1.60.31

Systolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisIncluding weight arms7-1.6-3.0 to -0.2<0.01

Systolic blood pressure (mmHg)6 to 12 monthsSubgroupingNormotensives3-2.3-3.1 to -1.60.31

Systolic blood pressure (mmHg)6 to 12 monthsSubgroupingUntreated hypertensives4-8.0-15.8 to -0.20.15

Systolic blood pressure (mmHg)13 to 60 monthsOverall meta-analysis4-1.1-1.8 to -0.40.46

Systolic blood pressure (mmHg)13 to 60 monthsSensitivity analysisAllocation concealment3-1.1-1.9 to -0.30.28

Systolic blood pressure (mmHg)13 to 60 monthsSensitivity analysisIncluding weight arms4-0.5-1.4 to 0.40.10

Systolic blood pressure (mmHg)13 to 60 monthsSubgroupingNormotensives3-1.1-1.9 to -0.30.28

Systolic blood pressure (mmHg)13 to 60 monthsSubgroupingUntreated hypertensives1-1.5-12.6 to 9.6-

Systolic blood pressure (mmHg)> 60 monthsOverall meta-analysis1-3.8-7.9 to 0.3-

Diastolic blood pressure (mmHg)6 to 12 monthsOverall meta-analysis5-1.2-1.8 to -0.60.31

Diastolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisDrop imputed standard deviationsimputed standar deviations no longer used for diastolic blood pressure

Diastolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisSmallest calculated standard deviationsimputed standar deviations no longer used for diastolic blood pressure

Diastolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisAllocation concealment3-1.2-1.8 to -0.60.28

Diastolic blood pressure (mmHg)6 to 12 monthsSensitivity analysisIncluding weight arms7-0.7-1.5 to 0.10.05

Diastolic blood pressure (mmHg)6 to 12 monthsSubgroupingNormotensives3-1.2-1.8 to -0.60.28

Diastolic blood pressure (mmHg)6 to 12 monthsSubgroupingUntreated hypertensives2-4.7-9.3 to 0.00.67

Diastolic blood pressure (mmHg)13 to 60 monthsOverall meta-analysis4-0.6-1.5 to 0.30.08

Diastolic blood pressure (mmHg)13 to 60 monthsSensitivity analysisAllocation concealment3-0.5-1.1 to 0.00.48

Diastolic blood pressure (mmHg)13 to 60 monthsSensitivity analysisIncluding weight arms4-0.3-1.0 to 0.40.06

Diastolic blood pressure (mmHg)13 to 60 monthsSubgroupingNormotensives3-0.5-1.1 to 0.00.48

Diastolic blood pressure (mmHg)13 to 60 monthsSubgroupingUntreated hypertensives1-7.0-12.5 to -1.5-

Diastolic blood pressure (mmHg)> 60 monthsOverall meta-analysis1-2.2-4.8 to 0.4-

Sodium excretion (mmol Na/ 24 hours)6 to 12 monthsOverall meta-analysis6-48.9-65.4 to -32.5<0.01

Sodium excretion (mmol Na/ 24 hours)6 to 12 monthsSensitivity analysisAllocation concealment4-43.6-62.6 to -24.6<0.01

Sodium excretion (mmol Na/ 24 hours)6 to 12 monthsSensitivity analysisIncluding weight arms6-44.3-58.4 to -30.2<0.01

Sodium excretion (mmol Na/ 24 hours)13 to 60 monthsOverall meta-analysis4-35.5-47.2 to -23.90.04

Sodium excretion (mmol Na/ 24 hours)13 to 60 monthsSensitivity analysisAllocation concealment4-35.5-47.2 to -23.90.04

Sodium excretion (mmol Na/ 24 hours)13 to 60 monthsSensitivity analysisIncluding weight arms4-33.3-42.0 to -24.60.05

Sodium excretion (mmol Na/ 24 hours)> 60 monthsOverall meta-analysis110.5-13.8 to 34.8-

DropoutsLatest follow upOverall meta-analysisDropouts in low sodium vs control groups10Relative risk = 1.040.86 to 1.250.55

 
Table 4. Meta-regression results, effects on SBP at 6 to 12 months

Explanatory variableSlope coef (95% CI)ConstantNo. of RCTs

Trials on normotensives and hypertensives

Mean baseline SBP-0.173 (-0.356 to 0.010)19.57

Mean change in urinary sodium excretion (6 to 12 months)0.013 (-0.049 to 0.075)-1.684

Mean age of participants at baseline0.118 (-0.188 to 0.424)-7.467

Trials of normotensives only

Mean baseline SBP-0.362 (-0.826 to 0.102)43.33

Mean change in urinary sodium excretion (6 to 12 months)0.013 (-0.057 to 0.084)-1.633

Mean age of participants at baseline-0.213 (-0.630 to 0.203)6.813



 
Table 5. Characteristics of systematic reviews on salt and blood pressure

ReviewInclusion criteriaRCTs only?Normo/ hyper tensiveMedian durationNo. trials (n)Fall in Na excretionWMD SBP (95%CI)WMD DBP (95%CI)Quality assessment

Graudal 1998Population: mean age >15 years, Intervention: low sodium or high sodium diet, no confounding, Outcome: urinary sodium excretion measured, systolic, diastolic or mean BP reportedYes, random allocation, parallel or crossoverNormotensive8 (4-1100) days56 (2581)weighted mean 160-1.2 (-0.6 to -1.8)-0.26 (+0.3 to -0.9)QA: subgrouping by open/ single blind or double blind method did not affect results. Notes: Statistical heterogeneity noted.

Graudal 1998Hypertensive28 (4-365) days58 (2161)weighted mean 118-3.9 (-3.0 to -4.8)-1.9 (-1.3 to -2.5)

Midgley 1996Population: human, not on antihypertensive drugs, Intervention: dietary sodium intervention, Outcome: diastolic and systolic BP measurement, urinary sodium excretionDesign: English language, full-length journal articlesYes, randomised controlled trials (crossover or parallel design).Normotensive14 (4-1095) days28 (2374)weighted mean 125 (95% CI 95-156)-1.6 (-2.41 to -0.89)-0.5 (-1.18 to 0.11)QA: Significant heterogeneity seen, reduced but not eliminated when studies sub-grouped according to quality characteristics.Notes: Evidence of publication bias provided.

Midgley 1996Hypertensive29 (4 - 730) days28 (1131)Weighted mean 95 (95% CI 71-119)-5.9(-7.77 to -4.12)-3.8 (-4.78 to -2.9)

Law 1991Population: not on antihypertensive drugs, Intervention: dietary sodium restriction, not confounded, Outcome: 24 hour urine collection, systolic and/or diastolic BPNo.Normotensive1.5 (0.7 to 16) weeks15 (?)Not statedNot statedNot statedQA: Quality not assessed.Notes: Individual trial data compared with pooled observational data, rather than pooled together

Law 1991Hypertensive5 (0.7 to 104) weeks63 (?)Not statedNot statedNot stated

Law 1991The review estimates that in people aged 50-59 a reduction in 50mmol Na /24 hours would lead to a fall of 5mmHg in systolic and 2.5mmHg in diastolic BP in normotensives, and a fall of 7 and 3.5mmHg respectively in hypertensives.

Cutler 1997Population: adult human, Intervention: sodium goals 28-273 mmol/24 hours, no confounding allowed, Outcome: lab-based measure of sodium intake, systolic and/or diastolic BP measuredYes, randomised controlled trials (crossover or parallel design), published onlyNormotensive1 (0.5 to 36) months12 (1689)Median ˜90 (range 16 to 210)-1.5 (-2.1 to -1.0)-0.8 (-1.3 to -0.3)QA: subgrouping by double blind or not had no significant effect on overall outcome.Notes: regression analyses used for publication bias failed to reject the null hypothesis.

Cutler 1997Hypertensive2 (1-24) months22 (1043)Median ˜71 (range 27 to 171)-3.8 (-4.9 to -2.8)-2.1 (-2.8 to -1.5)

Alam 1999Population: human elderly (>50 years), Intervention: changes in dietary NaCl, Outcome: blood pressureYes, published English-language randomised controlled trials, crossover or parallelNormotensive (2 trials) or with essential hypertension (9 trials)14 (9-104) weeks11 (485)Median 80 (range 23 to 260)-5.6(-6.9 to -4.3)-3.5 (-4.4 to -2.6)QA: quality assessment score tended to be high (average score >70%)

Ebrahim and Davey Smith 1998Ebrahim and Davey Smith 1998Population: adult humans, Intervention: dietary sodium reduction vs. control, Outcome: diastolic and systolic BP measurement, urinary sodium excretionYes, randomised controlled trials of at least 6 months durationNormotensiveNot stated2 (1095)Not stated-1.3 (-2.7 to +0.1)-0.8 (-1.8 to +0.2)QA: Quality not assessed.

Ebrahim and Davey Smith 1998HypertensiveNot stated6 (466)Not stated-2.9(-5.8 to 0.0)-2.1 (-4.0 to -0.1)

This review, 6 to 12 monthsPopulation: adult human, Intervention: sodium reduced diet vs. usual diet, Outcome: urinary sodium excretion, systolic and/or diastolic BP measurements taken 6 to 12 months or more than 12 months after interventionYes, parallel randomised controlled trialsNormotensive6 (6 to 12) months3 (2124)Weighted mean 43 (95% CI 16 to 70)-2.3 (-3.1 to -1.6)-1.2 (-1.8 to -0.6)QA: Sensitivity analysis (removing trials where allocation concealment is poor or unclear) had no effect on direction or significance of results

This review, 6 to 12 monthsHypertensive12 (12 to 12) months4(179)weighted mean 48 (95% CI 33 to 63)-8.0 (-15.8 to -0.2)-4.5 (-8.7 to -0.4)

This review, 13 to 60 monthsNormotensive36 (18 to 36) months3 (2285)weighted mean 34 (95% CI 19 to 50)-1.1(-1.9 to -0.3)-0.5 (-1.1 to 0.0)

This review, 13 to 60 monthsHypertensive24 months1(62)weighted mean 40 (95% CI 22 to 57)-1.5 (-12.6 to 9.6)-7.0 (-12.5 to -1.5)