Cardiovascular Journal of Africa: Vol 32 No 4 (JULY/AUGUST 2021)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 32, No 4, July/August 2021 AFRICA 217
consumption (as reference) for the incidence of CVD events
reported in the included studies, we computed the log of RR and
the matching standard error for the overall pooled RR (95% CI)
for the incidence of CVD events and by subgroup stratification
[cerebral infarction, cerebral haemorrhage, coronary heart disease
(CHD), etc.] using an inverse-of-variance method for weighting
in all quantitative estimations for dichotomous outcomes.
The degree of heterogeneity was assessed using I2 statistics
assuming a fixed-effect model (where I2 < 50%) or a random-
effect meta-analysis model if I2 > 50%. The fixed-effect model
presupposes the effect size is likely relatively similar across
studies in the meta-analysis.37,38 However, a random-effect model
ideates the difference in effect estimates across studies are valid
but follows a normal distribution. Publication bias for the likely
effect estimate of GLV intake on CVD events was tested using
funnel plots.
The constancy of the pooled RR (95% CI) was tested using
the leave-one-study-out method (carrying out the meta-analysis
several times, excluding a study at a time). All quantitative
analyses were conducted at p < 0.05 using the RevMan 5.4
software.39
Results
Over 3 000 records were retrieved from the literature search in
Google Scholar, EMBASE, MEDLINE, HINARI and Cochrane
Library but 1 021 duplicates were excluded. Also, 2 011 records
were excluded after screening the titles and abstracts (Fig. 1). On
full-text assessment, 65 records were excluded and 17 prospective
reports (five reports on composite CVD events,10,25-27,40 five reports
on coronary heart disease,28,41-44 one report on heart failure45 and
Table 1. Characteristics of prospective reports included in the meta-analysis
First author
Study characteristics
GLV intake
Baseline/outcomes evaluation
Year Country Incidence Total CVD event(s) Assessment Ascertainment
Gaziano JM 1995 United States < 1 s/d* vs ≥ 1 s/d 161 1 299 CVD Relative-reported deaths ‡† Not reported
Joshipura KJ 1999 United States Increment of 1 s/d 3 366W
204M
75 596W
38 683M
Ischaemic
stroke
Self/relative report ‡ National Stroke Soci-
ety (NSS) criteria
Joshipura KJ 2001 United States Increment of 1 s/d2,3 1 127W
1 063M
84 251W
42 148M
CHD Self/relative report ‡ World Health Organ-
isation (WHO) criteria
Johnsen SP 2003 Denmark 1.4 g/d* vs 28.00 g/d 266 54 506 Ischaemic
stroke
Self/relative report ‡ WHO criteria
Sauvaget C 2003 Japan ≤ 1 s/week* vs 1 s/d2 1 926 40 349 Stroke Stroke mortality‡ WHO criteria
Hung HC 2004 United States Increment of 1 s/d 3 3 864 109 635 CVD Self/relative report ‡ NSS criteria
Takachi R 2007 Japan Not reported 1 386 77 891 CVD MI or stroke diagnosis using CT
scan/MRI‡
WHO and NSS
criteria
Joshipura KJ 2009 United States Not reported 1 852W
2 040M
70 870W
38 918M
Ischaemic
CVD
Self/relative report ‡ WHO and NSS
criteria
Bendinelli B 2010 Italy ≤ 17.60 g/d* vs > 50.80 g/d1 144 29 689 CHD ©Self/relative report‡ Minnesota Code
Oude Griep LM 2011A Netherlands 34 g/d* vs 105 g/d2,3 233 20 069 Stroke Population and hospital discharge
register
Dutch guidelines
Oude Griep LM 2011B Netherlands 34 g/d* vs 105 g/d2,3 245 20 069 CHD ©Population and hospital
discharge register
WHO criteria
Larsson S 2013 Sweden < 2.3 s/d* vs > 6.0 s/d1,2,3 4 089 74 961 Stroke Self report‡ Not reported
Bhupathiraju SN 2013 United States 0.22 s/d* vs 1.50 s/day1,2 6 189 71 141 CHD Self/relative report ‡ WHO criteria
Rautiainen S 2015 Sweden < 0.2 s/d* vs > 1 s/d1,2,3 3 051 34 319 Heart failure Heart failure diagnosis and related
deaths ‡
ESC criteria
Wang JB 2016 China Increment of twice/week 355 2 445 Stroke Case, pathology, cytology, X-rays,
biochemical, ultrasound, endos-
copy and surgery reports
Team of reviewers
Buil-Cosiales P 2016 Spain 32·16 g/d* vs 113.00 g/d1 342 7 216 CVD Self/relative report ‡ Team of reviewers
Blekkenhorst LC 2017 Australia Intake per 10 g/d 238 1 226 CHD CHD diagnosis and related death ‡ Not reported
*Reference group for comparison; 1energy-adjusted dietary intakes of GLV; 2 additionally adjusted for other intakes, etc; 3 using median values of quintiles; Mmen; Wwom-
en; ©MI events, coronary revascularisation, or both not preceded by any other CHD event; ‡authenticated via vital statistics or medical records or designated registry;
†validated death certificate.
g/d – grams per day; s/d – servings per day; GLV – green leafy vegetables; ESC – European Society of Cardiology; CVD – cardiovascular disease; CHD – coronary heart
disease; CT – computed tomography; MI – myocardial infarction; MRI – magnetic resonance imaging.
Table 2. Methodological assessment of prospective studies
using the Newcastle–Ottawa scale
Study Year
Selection
Compa-
rability Outcome Total
Scores
Risk of bias
of included
studies S1 S2 S3 S4 C1 O1 O2 O3
Gaziano et al. 1995 1 1 1 1 1 1 6 High
Joshipura et al. 1999 1 1 1 1 2 1 1 1 9 Low
Joshipura et al. 2001 1 1 1 1 2 1 1 8 Moderate
Johnsen et al. 2003 1 1 1 1 2 1 1 8 Moderate
Sauvaget et al. 2003 1 1 1 2 1 1 1 8 Moderate
Hung et al. 2004 1 1 1 1 2 1 1 1 9 Low
Takachi et al. 2007 1 1 1 2 1 1 7 Moderate
Joshipura et al. 2008 1 1 1 1 2 1 1 8 Moderate
Bendinelli et al. 2010 1 1 1 1 2 1 1 1 9 Low
Oude Griep et al. 2011A 1 1 1 1 2 1 1 1 9 Low
Oude Griep et al. 2011B 1 1 1 1 2 1 1 1 9 Low
Larsson et al. 2013 1 1 1 1 2 1 1 1 9 Low
Bhupathiraju et al. 2013 1 1 1 1 2 1 1 1 9 Low
Rautiainen et al. 2014 1 1 1 1 2 1 1 1 9 Low
Buil-Cosiales et al. 2016 1 1 1 1 2 1 1 1 9 Low
Wang et al. 2016 1 1 1 2 1 1 1 8 Moderate
Blekkenhorst et al. 2017 1 1 1 1 2 1 1 1 9 Low
Risk of bias of included studies: high risk of bias: ≤ 6; moderate risk of bias: 7–8;
low risk of bias: 9 and empty cells indicate a score of 0.
S1 – representativeness of the exposed cohort; S2 – selection of the non-exposed
cohort; S3 – ascertainment of exposure; S4 – demonstration that outcome of interest
was absent at the start of the study; C1 – comparability of the cohort based on the
design or analysis; O1 – assessment of outcome; O2 – was follow up long enough for
outcomes to occur?; O3 – adequacy of follow up of cohorts.