Nigella: benefits, dosage, contraindications

Antiallergic

Antihistaminic effects have been demonstrated in human and animal studies. A decrease in the synthesis of pro-inflammatory leukotrienes via an inhibitory action on the arachidonic pathway has been described. Immunomodulatory effects have also been reported. The intake of nigella (black seeds) improves the ability of immune cells, polymorphonuclear leukocytes, to engulf and destroy pathogens in patients undergoing immunotherapy for allergies.

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Anticancer

It has been shown that thymoquinone, the main active constituent of black seed, possesses a number of anticancer properties mediated by different mechanisms. In vitro and in vivo studies have identified antiproliferative actions, induction of apoptosis, cell cycle arrest, generation of reactive oxygen species, and antimetastatic/antiangiogenic effects.nnThymoquinone interacts with several key molecular elements (p53, p73, PTEN, STAT3, PPAR-g and caspase activation), which contribute to inhibiting the growth of various types of cancer cells. These cells include those from several cancers such as neuroblastoma, pancreatic, breast, ovarian, colorectal, bone, lung and certain forms of leukemia.nnFurthermore, laboratory models have shown that a combination of thymoquinone and chemotherapeutic agents, such as doxorubicin or cisplatin, has a greater effect than chemotherapy alone. Encapsulation of thymoquinone in nanoparticles could enhance the antiproliferative, anti-inflammatory and chemosensitizing effects of thymoquinone, according to the results of one study. While thymoquinone appears to be the most promising anticancer constituent of Nigella sativa, other constituents such as α-hederin and derivatives of these two compounds have also been identified as having therapeutic potential.nn

Anti-inflammatory

Anti-inflammatory effects of certain constituents of Nigella sativa likely play a role in its potential clinical effects. It has been shown that dithymoquinone, thymohydroquinone, thymol, carvacrol, and thymoquinone induce anti-inflammatory effects by inhibiting cyclooxygenase-1 (COX-1) and/or cyclooxygenase-2 (COX-2) in laboratory research. Some evidence also suggests that they reduce the production of certain inflammatory cytokines. In addition, clinical research shows that consumption of black seeds reduces levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, or C-reactive protein (CRP). In a meta-analysis, CRP was reduced compared with placebo in patients with conditions associated with a low-grade chronic inflammatory state, such as obesity, non-alcoholic fatty liver disease (NAFLD), metabolic syndrome, and rheumatoid arthritis.

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Respiratory effect

Nigella is traditionally used for respiratory disorders. Laboratory research suggests that nigella can relax the smooth muscle of the trachea. Nigella essential oil acts on various receptors in the body. It opposes the action of a receptor linked to muscle contraction (muscarinic), reduces the activity of a receptor associated with allergic reactions (histamine H1), and influences calcium channels. Additionally, it activates receptors that help relax smooth muscle. Thymoquinone, a component of the oil, may contribute to these anti-inflammatory effects.

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Neurological

Black seed oil is an inhibitor of acetylcholinesterase, reduces tumor necrosis factor-α (TNF-α) and increases brain-derived neurotrophic factor. In one study, the thymohydroquinone was identified as a compound with the strongest AChE inhibitory effect. By increasing acetylcholine, AChE inhibitors have been found useful for treating apathy, autism, dementia, Alzheimer's disease, schizophrenia and Parkinson's disease. Alzheimer's disease is a slowly progressive neurodegenerative disorder of the central nervous system, characterized by a profound impairment of cognitive functions and memory. Pathologically, it is marked by progressive brain atrophy, accumulation of cortical senile plaques and neurofibrillary tangles. A fibrillar amyloid substance is deposited in the senile plaques, formed by aggregation of the beta-amyloid peptide (Aβ). A study in rats suggests that thymoquinone has neuroprotective potential against Aβ in rat hippocampal and cortical neurons and may therefore be a promising candidate for the treatment of Alzheimer's disease. In other animal models, the oil or seed extract was found to improve learning and memory and may protect against cell loss and neurodegeneration.

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Antioxidant

Antioxidant effects have been reported in several in vitro and animal studies, mainly attributed to the constituent thymoquinone. Cold-pressed Nigella seed oil has been shown to yield higher levels of thymoquinone than oil extracted by other techniques. A preliminary clinical study of 30 postmenopausal women reported that Nigella oil, at 3 g/day for 12 weeks, increased levels of the enzymes superoxide dismutase and glutathione peroxidase. Another study suggested that the majority of thymoquinone's beneficial effects are primarily related to modulation of the Nrf2 signaling pathway. Thymoquinone stimulates its activity, encouraging Nrf2 gene expression and promoting its translocation to the cell nucleus. This process plays an important role in protecting cells against stress and damage. Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that, in humans, is encoded by the NFE2L2 gene. According to preliminary research, NRF2 may regulate the expression of antioxidant proteins that protect against oxidative damage triggered by injury and inflammation. Several drugs that activate the NFE2L2 pathway are under investigation for the treatment of diseases caused by oxidative stress.

Antimicrobial

Antibacterial actions have been observed in vitro against Staphylococcus aureus, Helicobacter pylori, and Streptococcus spp. Antiparasitic effects have been identified in animal and human studies against Schistosoma mansoni, which may be due to antioxidant and immunomodulatory effects. It has also been shown that the extract and the black seed oil have antifungal effects, particularly against species of Candida and Aspergillus, probably by inhibiting germination of dermatophyte arthrospores, supporting the traditional use of black seeds for fungal skin infections.

Hypoglycemic

Animal and preliminary human studies on Nigella (black seed) and its constituent thymoquinone have shown improvements in glucose tolerance, antioxidant status, and renal function, and decreases in blood glucose, serum insulin, and glycated hemoglobin levels. Proposed mechanisms of action include reduced hepatic glucose production and inhibition of nitric oxide pathways.

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Hepatoprotective

Animal studies indicate that Nigella has protective effects on the liver, acting against various toxic agents. Among its components, thymoquinone plays a key role in reducing liver fibrosis, notably by acting on specific cellular pathways (such as Toll-like receptor 4 and phosphatidylinositol 3-kinase). A meta-analysis of clinical research shows that taking Nigella seeds in the form of oil or powder has beneficial effects on alkaline phosphatase (ALP) and aspartate aminotransferase (AST) levels when used for at least 12 weeks. No effect was observed on alanine aminotransferase (ALT) levels. The potential hepatoprotective effects are likely due to a decrease in oxidative stress.

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Immunomodulatory

Nigella seed is considered for its beneficial effects on the immune system. Preliminary studies indicate it may help reduce drops in hemoglobin and leukocytes often observed after chemotherapy. It also appears to stimulate the production of certain human interleukins and influence macrophage activity. Animal research has suggested that Nigella essential oil can affect the number and activity of neutrophils and other lymphocytes, and may even reduce antibody production.

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Analgesic

Black seeds are traditionally used orally or topically to treat arthritis, headaches and other pains. nnExtracts, the oil and constituents of Nigella have all shown analgesic effects in animal models. This is likely due to the anti-inflammatory or central nervous system (CNS) depressant constituents of Nigella.nn

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Gastroprotective

Gastroprotective mechanisms have been observed in an animal study. Thymoquinone has been reported to inhibit proton pump activity and acid secretion, while increasing mucin secretion and nitric oxide production.nnFurthermore, nigella seeds are used to reduce ulcers. Potential mechanisms of action appear to include the antioxidant or anti-inflammatory effects of black seed constituents such as thymoquinone, antibacterial effects against H. pylori, or protection of the stomach lining against acid. nn

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Hypotensive

Some animal and human research suggests that nigella and its constituents may reduce blood pressure. Potential mechanisms of action include diuresis, regulation of endothelial function, or inhibition of calcium channels. nn

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Antiparasitic

Black seeds have historically been used against parasites. Black seed extract has shown antiparasitic effects against various types of parasites, probably by inhibiting egg-laying.