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

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 32, No 4, July/August 2021

216

AFRICA

Apromising preventative strategy for CVD is diet.

10-13

However,

studies on the potential association of diet and CVD events have

focused on the effect of red meat,

14,15

salt intake,

alcohol,

saturated fats/oils and dairy products.

Prior reviews and meta-

analyses

19-24

investigating the effect of fruit and vegetables on the

risk profile for CVD have focused on broad categories of the

nutritional modalities. For example, Deng

et al.

and Kwok

in two reviews of meta-analyses assessed the effect of fruit

and vegetable intake, in general, on the burden of diseases and

all-cause mortality without providing information on the specific

effect(s) of green leafy vegetables (GLV) on the incidence of

distinct CVD events.

The information provided by individual studies on the

effect of GLV intake remains inconclusive. While some studies

reported a reduction in the incidence of CVD events with

higher consumption of GLV,

10,25,26

others observed statistically

insignificant relationships.

27,28

The pooled effect of GLV intake

on incident CVD is currently unknown.

GLV are widely available in LMIC.

The vegetables are rich

in phytochemicals and micronutrients known to be essential for

health.

13,30-32

Also, GLV contain folic acid, vitamins A, C, E and K,

as well as high amounts of calcium, iron, potassium, phosphorous

and zinc,

33,34

which may be protectively associated with CVD

risk.

This systematic review and meta-analysis investigated the

pooled effect of GLV intake on incident CVD events.

Methods

The systematic review was registered in the international

prospective register of systematic reviews and is accessible

via

https://www.crd.york.ac.uk/prospero/display_record.

php?ID=CRD42020181050. Google Scholar, EMBASE,

MEDLINE, HINARI and Cochrane Library were searched

(in December 2020 using specific search terms independent

of language and publication dates) for previously published

epidemiological reports on consumption of GLV and CVD. The

following search terms were used.

EMBASE, Google Scholar and Cochrane Library search

terms: ‘vegetables’ OR ‘chlorophyll-containing vegetables’ OR

‘green leafy vegetables’ OR ‘broccoli’ OR ‘cabbage’ OR ‘celery’

OR ‘collard green’ OR ‘green pea’ OR ‘lettuce’ OR ‘spinach’ OR

‘swiss chard’ OR ‘turnip green’ AND ‘cardiovascular disease’ OR

‘cerebrovascular disease’ OR ‘cerebral infarction’ OR ‘cerebral

haemorrhage’ OR ‘coronary heart disease’ OR ‘heart failure’ OR

‘subarachnoid haemorrhage’.

MEDLINE and HINARI search terms using PubMed

interphases:

‘vegetables (Title/Abstract)’ OR ‘green leaves (Title/

Abstract)’ OR ‘edible green leaves (Title/Abstract)’ OR ‘green

vegetables (Title/Abstract)’ OR ‘leafy vegetables (Title/Abstract)’

OR ‘green leafy vegetables (Title/Abstract)’ OR ‘chlorophyll-

containing vegetables (Title/Abstract)’ OR ‘broccoli (Title/

Abstract)’ OR ‘cabbage (Title/Abstract)’ OR ‘celery (Title/

Abstract)’ OR ‘collard green (Title/Abstract)’ OR ‘green pea

(Title/Abstract)’ OR ‘lettuce (Title/Abstract)’ OR ‘spinach (Title/

Abstract)’ OR ‘swiss chard (Title/Abstract)’ OR ‘turnip green

(Title/Abstract)’ AND ‘stroke (MesH terms)’ OR ‘transient

ischemic attack (MeSH terms)’ OR ‘haemorrhagic stroke (MeSH

terms)’ OR ‘ischaemic stroke (MeSH terms)’ OR ‘cardiovascular

disease (MeSH terms)’ OR ‘cerebrovascular disease (MeSH

terms)’ OR ‘cerebral infarction (MeSH terms)’ OR ‘cerebral

haemorrhage (MeSH terms)’ OR ‘coronary heart disease (MeSH

terms)’ OR ‘heart failure (MeSH terms)’ OR ‘subarachnoid

haemorrhage (MeSH terms)’. Details of the literature search are

in the PRISMA flow chart (Fig. 1).

Study assessment for inclusion and exclusion criteria and

data extraction were conducted by two independent assessors

(AO and APO) based on the descriptions in the original

article. Only studies with usable data and appropriate analytical

techniques were included in the meta-analysis. The following

information was extracted from each included study: first author

name, publication year, sample size, average follow-up time, the

incidence of CVD, adjusted relative risk (RR)/hazard ratio and

95% confidence interval (CI), etc.

Studies included in this meta-analysis were prospective cohort

reports (where the primary exposure was GLV consumption and

outcomes were CVD events) only. Where there are significant

levels of data overlap among published studies, the study with

complete evidence was included in the quantitative synthesis.

A methodological assessment for risk of bias of included

studies was conducted (independently by two members of the

review team) using the Newcastle–Ottawa scale for quality

assessment of observational reports

following the Cochrane

Collaboration guidelines.

Statistical analysis

Using the RR and 95% CI for highest quintile/category of GLV

consumption compared to the lowest quintile/category of GLV

Records retrieved via electronic catalogue search

Google Scholar, EMBASE, MEDLINE, HINARI and

Cochrane Library (

= 3 132)

Full-text articles appraised for eligibility (

= 85)

Identification

68 full-text articles exempted, with reasons:

• 29 without data on GLV

• 18 animal and

in vitro

studies

• 14 reviews, abstract, letters and case report

• 6 cross-sectional reports

• 1 registered trial

Articles eligible for inclusion (

= 17)

Prospective studies (17)

Eligibility

Included

Screening

Records after excluding duplicates (

= 2 102)

1 030 duplicates excluded

2 017 records excluded after

examining titles and abstracts

Fig. 1.

PRISMA flowchart describing selection of the stud-

ies for the meta-analysis