Effects of Black Seed on Cardiovascular and Other Diseases
Black seed has been one of the most important medicinal plants used throughout history. Modern studies have demonstrated that black seed and its bioactive components possess antioxidant, antidiabetic, antibacterial, anticancer, antifungal, antitumoral, anticonvulsant, anti-inflammatory, anti-ulcer, hypoglycemic, and immune-enhancing properties.
Belonging to the Ranunculaceae family, black seed is widely cultivated in North Africa, Central Asia, Southern Europe, and in Turkey—particularly in the provinces of Isparta, Konya, Afyonkarahisar, Kütahya, Burdur, and the Çukurova region. Depending on the region where it is grown, it is known by different names: black cumin in the United Kingdom, black caraway seed in the United States, and black seed or black grain in Arabic-speaking countries.
In Turkey, the plant flowers in June–July, and its fruit is a multi-seeded capsule. When mature, the capsule opens and the seeds turn black. The seeds—oval, triangular, and 2–3 mm in size—are the most widely used part of the plant. Of the 20 known Nigella species, 13 grow naturally in Turkey. The most commonly cultivated and commercially traded species is Nigella sativa. The name Nigella derives from the Latin word nigellus, meaning “blackish,” referring to the color of the seeds.
The major bioactive constituents of black seed include thymoquinone, thymohydroquinone, and dithymoquinone, with thymoquinone recognized as the primary active compound. It has been reported that thymoquinone should constitute no less than 18% of the oil for optimal biological activity. Black seed contains carbohydrates, fats, vitamins, minerals, and all eight essential amino acids. It is also rich in fatty acids such as oleic, linolenic, linoleic, arachidonic, palmitoleic, and stearic acids. Additionally, it contains carotene, saponins, flavonoids, indazole-type alkaloids, cardiac glycosides, potassium, phosphorus, calcium, and iron.
Black seed has a remarkable historical significance. Originating in Anatolia, it later spread to Egypt, Syria, India, Africa, and Europe. Archaeological studies have identified black seed in the tomb of Pharaoh Tutankhamun (1325 BC), believed to have been placed there as a symbol of health and well-being in the afterlife. Cleopatra reportedly used black seed oil for beauty and health, it was used as a spice in Roman times, and it was known in ancient Mesopotamia. Hippocrates recommended its use for digestive complaints and liver strengthening. Ancient Egyptian and Greek physicians used it for toothaches, migraines, nasal congestion, intestinal parasites, menstrual regulation, and to promote lactation. In the works of Hippocrates and Dioscorides, it appears under the name Melanthion.
The saying of Prophet Muhammad (PBUH), “Black seed is a remedy for every disease except death,” emphasizes its perceived healing potential. Ibn Sina (Avicenna) described it in The Canon of Medicine (1031) as a plant that stimulates metabolism and alleviates fatigue and weakness.
Cardiovascular and Metabolic Effects
Oxidative stress caused by free radicals plays a key role in the pathogenesis of many diseases, including atherosclerosis, diabetes, hypertension, and cancer. Studies have shown that thymoquinone in black seed oil prevents lipid peroxidation in liposomes, thereby inhibiting oxidative stress. Black seed oil has been shown to reduce lipid peroxidation in conditions such as cerebral and cardiac ischemia, arteriosclerosis, rheumatism, and cancer.
Diabetes is an inflammatory disease that predisposes individuals to various cardiovascular conditions. In experimental studies, thymoquinone administered to diabetic mice for four weeks significantly reduced blood glucose levels. It is suggested that thymoquinone decreases hepatic gluconeogenesis, contributing to this effect. Other studies have shown that black seed oil lowers blood glucose in diabetic animals without causing side effects, likely due to increased insulin secretion by the pancreas.
Kaatabi et al. repeated their previous three-month study to investigate long-term effects and administered black seed (2 g/day) for one year to individuals with type 2 diabetes using oral hypoglycemic agents. Compared with the control group, the intervention group showed significant reductions in fasting blood glucose and HbA1c levels. Insulin resistance decreased and β-cell activity increased significantly throughout treatment. Another study evaluating cardiac function in type 2 diabetics using black seed supplements for one year found no change in HbA1c in the non-supplemented group, whereas the supplemented group had a significant reduction.
Thymoquinone in black seed has been shown to lower arterial blood pressure and heart rate. Part of the antihypertensive effect is believed to result from its diuretic properties.
The essential oils in black seed may reduce blood cholesterol levels by inhibiting or diminishing hepatic HMG-CoA reductase activity. In a study by Najmi et al., participants with insulin resistance were given black seed oil (2.5 mL twice daily) in addition to atorvastatin and metformin for six weeks. Compared with the group receiving only atorvastatin and metformin, the group receiving black seed showed a significantly greater reduction in total cholesterol and LDL cholesterol. However, changes in triglycerides and HDL cholesterol were similar between groups. Elevations in liver enzymes were noted in the statin-only group.
Safety and Toxicity
Although toxicity studies indicate a wide margin of safety, case reports in the literature describe acute kidney injury and allergic reactions caused by black seed. Changes in hemoglobin metabolism, reductions in serum cholesterol, triglycerides, glucose levels, leukocyte count, and platelet count have also been reported. These effects are thought to be associated with thymoquinone, although the exact mechanism is unclear. Researchers emphasize the need to monitor changes in hemoglobin metabolism and alterations in leukocyte and platelet levels during use.While black seed offers numerous reported health benefits, it must be remembered that it is not a medication. Individuals wishing to use it as a supplement should do so under medical supervision, taking into account existing health conditions, medications, and laboratory findings. It is advisable to use standardized preparations sold in pharmacies and to maintain regular follow-up.
