Green leafy vegetables are edible leaves of plants and are important components of a balanced. They are consumed alone or alongside other dishes as sauces or soups. Green leafy vegetables are packed with nutrients predominantly bioactive compounds that have been reported to promote a healthy state and ameliorate disease conditions. These bioactive compounds exert antioxidant, anti-inflammatory and other biological activities. Non-communicable diseases including cancers, cardiovascular and metabolic diseases have been reported to be aggravated by inflammation and oxidative stress. This paper, therefore, aimed to provide the scientific validation for the selected green-leafy vegetables as anti-inflammatory and anti-cancer agents. Databases including PubMed, Google Scholar and ScienceDirect were used to perform the search. The reviewed vegetables include Vernonia amygdalina, Corchorus olitorius, Talinum triangulare, Telfairia occidentalis, Gongronema latifolium, Moringa oleifera and Celosia argentea. Although the antioxidant, anti-inflammatory and cytotoxic properties of these vegetables were presented, detailed studies from multiple researchers were scanty. Therefore, further studies on these vegetables are encouraged to have sufficient data to ascertain scientific validation for anti-inflammatory and anti-cancer claims.

Oxidative stress is a global phenomenon that describes the imbalance between the number of pro-oxidants and antioxidants in favour of pro-oxidants [1]. Pro-oxidants notably reactive oxygen species and reactive nitrogen species such as nitric oxide, singlet oxygen, lipid peroxides are elevated in the state of oxidative stress in contrast to reduced levels of endogenous antioxidant defence molecules such as superoxide dismutase, glutathione peroxidase, catalase, etc. [2]. A lot of the natural processes that take place in the human body generate free radicals which are the culprits of oxidative stress. Free radicals are necessary for some biological processes that are essential for life, acting as signal molecules at low concentrations in cellular pathways [3], however, excessive generation of free radicals causes the damage of tissue macromolecules (proteins, lipids and DNA) leading to structural modifications as well as cellular dysfunctions [4,5].

High amounts of free radicals have been implicated in the outset of many diseases including cancer; a disease that has been reported to result from DNA damage thus affecting the cell cycle6. The development of cancer is an intricate process that implicates oxidative stress, inflammation and genetic makeup, which are triggered by both exogenous and endogenous factors [7,8]. Elevated oxidative stress in cancer cells is aggravated by metabolic changes and mitochondrial dysfunctions, thereby enhancing the expression of the cell survival protein - nuclear factor erythroid 2-related factor 2 (NRF-2) which encourages the progression of cancer [6].

About 25% of all cancers have been associated with inflammatory reactions [9]. Cancer cells are in a hyperactive state of oxidative stress as a result of increased metabolism and ROS [10]. Reactive oxygen and nitrogen species within the inflammatory microenvironment, damage tissue macromolecules including proteins, DNA and lipids. Accumulation of the damaged cells leads to the generation of cancer stem cells [10]. This process facilitates the recruitment of inflammatory cytokines such as interleukin-6, which in turn aggravates the generation of superoxide (O2•−) and nitric oxide radicals through the inducible nitric oxide synthase (iNOS) and nicotinamide adenine dehydrogenase (NADH) pathways. Furthermore, at the level of gene expression, reactive oxygen/nitrogen species and pro-inflammatory cytokines stimulate the expression of DNA methyltransferase-1 protein leading to DNA methylation of tumour suppressor genes [11].

Free radicals are degraded by the body’s natural defence system, supported by exogenous antioxidant compounds such as vitamins, minerals, and some phytochemicals including polyphenols, flavonoids and others [6]. Plants are beneficial to humans for the management of diseases owing to the presence of phytochemicals (bioactive compounds) present in them [12]. There are epidemiological shreds of evidence for the role of bioactive compounds in combating human diseases such as cancer, diabetes, cardiovascular diseases and others [13]. Green-leafy vegetables are important components of a balanced diet and they are rich in many beneficial bioactive compounds including terpenoids and polyphenols. The anti-inflammatory and anticancer properties of seven green-leafy vegetables including Vernonia amygdalina, Corchorus olitorius, Talinum triangulare, Telfairia occidentalis, Gongronema latifolium, Moringa oleifera and Celosia argentea were reviewed in this paper. The objective of this review is to provide scientific validation for the selected green-leafy vegetables as anti-inflammatory and anti-cancer agents, with the hope of promoting their cultivation, utilisation and consumption.

Scientific databases including ScienceDirect, PubMed and Google Scholar were used to search for available literature on the selected green-leafy vegetables for anti-inflammatory and anti-cancer properties. Keywords including “anticancer”, “anti-inflammatory”, “green-leafy vegetables”, “Nigeria”, “Vernonia amygdalina”, “Corchorus olitorius”, “Talinum triangulare”, “Telfairia occidentalis”, “Gongronema latifolium”, “Moringa oleifera” and “Celosia argentea” were used for the search. 

Information about the plants presented includes; family, scientific and common names, phytochemicals present and biological activities reported. Seven green leafy vegetables commonly consumed in soups or sauces along with staple meals whose anti-inflammatory and anticancer properties have been reported were identified. These vegetables include Vernonia amygdalina, Corchorus olitorius, Talinum triangulare, Telfairia occidentalis, Gongronema latifolium, Moringa oleifera and Celosia argentea.

Vernonia amygdalina: Vernonia amygdalina is a shrub popularly grown in Africa both for its medicinal and culinary properties. It belongs to the family- Asteraceae, and is commonly called ‘bitter leaf’. As the name implies, the shrub has a characteristic bitter taste which can be reduced by washing and discarding the water several times before use for culinary purposes, but for medicinal purposes, the bitter extract is consumed rather than being discarded. In Nigeria, extracts of bitter-leaf are used to manage many diseases including diabetes, malaria, hypertension, cough, blood tonic, etc14. Phytochemicals present include flavonoids, saponins, tannins, oxalates, sesquiterpene lactones, phenolic acids, xanthones, etc. [15]. Biological activities reported for V. amygdalina include antibacterial, antimalarial, antifungal, anticancer, antioxidant, hypoglycaemic, hepatoprotective, analgesic, antihypertensive, etc [16]. The cytotoxicity of V. amygdalina against 4T1 breast cancer cells showed that the n-hexane, ethyl acetate and ethanol fractions exerted an inhibition concentration of 1860.54±93.11, 25.04±0.36 and 1940.84±96.37 µg/ml respectively [16]. Furthermore, Johnson et al. reported that methanol extract of V. amygdalina exerted a cytotoxic effect on PC-3 Human Prostate Carcinoma cells, using the trypan blue test, cell morphology analysis and the MTT assay [17]. In an earlier report, extract of V. amygdalina exerted apoptotic effects on MCF-7 breast cancer cells [18]. The ability of extract of V. amygdalina to modulate oxidative stress in cancer cells has also been reported.

Corchorus olitorius: Corchorus olitorius is a popular vegetable in Nigeria and West Africa, it is commonly called ‘ewedu’ by the Yoruba people. The plant belongs to the Malvaceae family and its English name is ‘Jute’ [19]. The leaves serve as a vegetable in a variety of soups and are slimy. Traditionally, the leaves of Corchorus olitorius are used to treat headaches, stomach problems, general pains, fevers, gonorrhoea, tumours and chronic cystitis [20,21]. It has also been used as a diuretic, purgative, and is employed to ease labour pains and delivery. Jute leaf contains good amounts of antioxidants like vitamin E, A, and C; and its antioxidant potential is highly employed in the management of many diseases including diabetes, heart disease as well as hypertension [22]. Phytochemicals present include alkaloids, saponins, cardiac glycosides, phenols and flavonoids, chlorogenic acids, phytol and monogalactosyldiacyl glycerol [21,23]. The biological activity carried out on the extract of Corchorus olitorius against cancer cell lines HeLa (cervical), HL460 (lung) and PC-3 (prostate), showed mild cytotoxicity at ≥800µM [21]. Ethanol extract of Corchorus olitorius exerted a reductive effect on viable cells based on results obtained from MTT assay carried out on MCF-7 breast cancer cell line [24].

Moringa oleifera: Moringa oleifera L of the family- Moringaceae, is a perennial angiosperm plant. The plant is native to the Himalayan region but is however currently domesticated in most tropical and sub-tropical countries of the world including Saudi Arabia [25]. Moringa leaves are edible and can be added to salads, rice or pasta or other dishes, soups. The leaves can be juiced, fried or steamed. Moringa leaf powder can also be used as a tea, added to beverages, sprinkled on food or taken in capsules. In folklore, various parts of the plant are employed in the treatment of diseases including ear and dental infections, hypertension, anaemia, cancer, diabetes, skin infections, respiratory infections and others [26]. Moringa leaves are a rich source of both micro-and macro-nutrients including digestible proteins, minerals, vitamins and phytochemicals such as alkaloids, cyanogenic glycosides, oxalates, saponins, phytates and tannins [27]. Some bioactive compounds reported conferring anticancer benefits including isopropyl isothiocynate, eugenol, D-allose, and hexadecenoic acid ethyl ester [28], have been identified in the ethanol extract of the leaves. Biological activities reported for moringa leaves include antioxidant, anticancer/antitumor, antidiabetic, antilipidemic, hepatoprotective and anti-inflammatory effects [29].  Cytotoxicity studies carried out on breast and colorectal cancer cell lines (MDA-MB-231 and HCT-8 respectively) using ethanol extract of leaves of moringa showed significant anticancer effect28. Treatment of both cancer cell lines with ethanol extract of moringa leaves showed a 90

Leafy vegetables are valuable food materials that supply enormous nutrients to humans. They contain numerous phytonutrients that can be harnessed to combat diseases associated with oxidative stress and inflammation. The growing rate of cancer incidence cannot be overemphasised and currently, there is no cure for cancer. Promoting the consumption of these vegetables can help to reduce the risk of these diseases. Furthermore, promoting the consumption of these vegetables will enhance their cultivation and increase revenue generation for farmers.

Conflict of interest

There is no conflict of interest among the authors.