Rosemary: benefits, dosage, contraindications

Hepatoprotective

The hepatoprotective effect of rosemary is linked both to the presence of carnosic acid, carnosol, and rosmarinic acid. The hepatoprotective action of carnosic acid and carnosol is thought to be due in part to their ability to maintain and increase the enzymatic activity of glutathione peroxidase and superoxide dismutase, whose activity is reduced in the presence of toxic agents. In vivo, rosemary has shown a protective effect against hepatic steatosis by decreasing hepatic triglyceride levels in rats fed a high-fat diet.

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Antioxidant

The antioxidant activity of rosemary is due to a variety of compounds, particularly phenolic diterpenes and phenolic acids such as rosmarinic acid. These antioxidant effects can contribute to membrane stabilization and to the reduction of free radical production, which may help the electron-donating capacity of rosemary diterpenes to protect membranes against oxidative damage.nnRosemary leaf extract has been shown to increase superoxide dismutase activity and has an effect stronger than that of vitamin E in trapping oxygen radicals.nnIn cell culture studies, rosemary extract at concentrations of 1/2000 and 1/1000 significantly inhibited nitric oxide (NO) production. It is suggested that carnosol and carnosic acid account for more than 90% of its antioxidant properties. Carnosic acid has been shown to have a photoprotective action on human dermal fibroblasts exposed to ultraviolet rays in vitro, and rosemary extract inhibits oxidative alterations of surface skin lipids both in vitro and in vivo, and enhances cell-mediated immunity in rats subjected to oxidative stress.nnRosmarinic acid has also been studied for its antioxidant activities and plays an important role in the antioxidant capacities of extracts containing very similar concentrations of diterpenes.nnIn one study, extracts with a lower concentration of rosmarinic acid (50:50) showed poorer antioxidant capacity, and the antioxidant activity was further enhanced by the presence of carnosol as the major diterpene content. Antioxidant activity was also studied in a model of macular degeneration. Sprague-Dawley rats received a test solution of rosemary intraperitoneally 1 hour before the start of the light exposure tests. Rosemary powder extract (34 mg/kg) alone and when combined with zinc (1.3 mg/kg) effectively reduced the extent of retinal light lesions. Treatment with rosemary (17 mg/kg) and zinc (1.3 mg/kg) reduced the expression of protein markers of oxidative stress and improved the survival of visual cells, as shown by improved photoreceptor cell morphology and decreased degradation of retinal DNA.nn

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Anti-inflammatory

In vitro research shows that rosemary extract can inhibit the activity of human leukocyte elastase, which plays a role in inflammation. Research indicates that rosemary may be able to induce a beneficial mechanism in cellular protection and the resolution of inflammation. Rosemary, and more particularly carnosol and carnosic acid, act by inhibiting the activation of 5-lipoxygenase and thus reduce pro-inflammatory responses in stimulated leukocytes. The ursolic acid from rosemary would inhibit the activation of the nuclear transcription factor kappa B (NF-κB). Some animal studies suggest that rosemary extract may prevent allergic airway inflammation by inhibiting the expression of interleukin (IL)-13.

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Cholagogue

A lyophilizate of an ethanolic tincture of rosemary dissolved in a perfusate was injected at doses corresponding to the crude drug of 0.5 g, 1 g or 2 g/kg body weight into the jugular vein of rats, under constant perfusion with a sodium taurocholate solution. A significant and rapid increase in bile flow was observed; it reached a maximum at 30 minutes then returned to baseline within 2 hours after 1 g or 2 g/kg, and within 1 hour after 0.5 g/kg. Intravenous administration of a lyophilized 15% alcohol extract of rosemary flowering tops to biliary-cannulated guinea pigs, at 100 mg/kg body weight, caused a 138% increase in bile flow at 30 minutes, followed by a slower period of activity, but which reached a second peak of 218% after 105-120 minutes. The results indicate both cholagogue and choleretic activity of the extract.

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Choleretic

The lyophilized ethanolic tincture of rosemary, dissolved in a perfusion fluid, at doses of 0.5 g, 1 g and 2 g/kg of drug, when administered into the jugular vein of rats treated with sodium taurocholate, causes a rapid increase in biliary flow, reaching a maximum at 30 minutes, then returning to a baseline flow.

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Antiallergic

In humans, rosmarinic acid would significantly improve the symptoms of seasonal allergies compared with a placebo. These effects would occur by inhibiting the induction of certain adhesion molecules and cyclooxygenase-2 (COX-2)1.

Anticancer

Animal research suggests that rosemary extract may decrease the incidence of carcinogen-induced tumors, tumor burden, and tumor yield. Rosemary extract and certain constituents, such as carnosic acid, appear to inhibit proliferation and may even induce apoptosis of leukemic cells. Other in vitro research suggests that rosmarinic acid, a constituent of rosemary, reduces expression of the pro-inflammatory gene cyclooxygenase-2 (COX-2). This gene could be a risk factor for cancer development. Rosemary extract and rosemary essential oil may also reduce cancer development by protecting DNA against oxidative damage; this is attributed to rosemary's phenolic constituents. In addition, rosemary polyphenols may reduce activation of procarcinogens and increase detoxification pathways. Other cell culture research suggests that carnosol, a constituent of rosemary, inhibits cancer cell metastasis by decreasing the activity of matrix metalloproteinase-9 (MMP-9).

Antimicrobial

Various cell culture studies show that rosemary essential oil and rosemary extract have antibacterial activity against Gram-negative and Gram-positive bacteria, including some drug-resistant strains and foodborne pathogens, as well as activity against certain yeast and fungal species, notably Candida albicans. Rosemary essential oils that contain higher amounts of camphor, borneol, and verbenone appear to exert the greatest antimicrobial activity. Rosemary extract containing carnosic acid, carnosol, and rosmarinic acid appears to have the highest antimicrobial activity. However, other research suggests that rosemary does not exhibit antifungal activity against Candida species.

Neurological

Rosemary shows promising potential for brain protection and the prevention of neurodegenerative diseases. It can inhibit certain brain enzymes, protect dopamine-producing neurons, and possess antidepressant and analgesic properties. Cell culture studies indicate that rosemary may promote nerve growth and protect against oxidative stress thanks to carnosic acid, which has neuroprotective effects by activating the brain's antioxidant defenses.nnThe effectiveness of carnosic acid depends on its ability to reach the brain. Research has shown that after oral administration in mice, carnosic acid crosses the blood-brain barrier well, suggesting potential application in the treatment of neurodegenerative diseases. Carnosic acid also increases antioxidant levels in the brain, which could contribute to its neuroprotective capacity. However, further studies are needed to better understand these mechanisms and their applicability in humans.nn

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Dermatological effect

It is thought that rosemary polyphenols — rosmarinic acid, carnosic acid, and carnosol — induce these photoprotective effects. In addition, rosemary essential oil has been shown to increase blood circulation at the hair follicles and help combat hair loss.nn

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Gastroprotective

Rosemary has potential antiulcer activity. A rosemary extract has demonstrated in vitro antibacterial activity against Helicobacter pylori (Mahady et al 2005). Dias and colleagues (2000) studied the antiulcerogenic activity of the crude hydroalcoholic rosemary extract in an experimental rat model. The extract was prepared from the treated, dried aerial parts of rosemary. In the ethanol-induced ulcer model, doses of 100 and 200 mg/kg of this extract showed no antiulcerogenic activity, whereas doses of 500 and 1000 mg/kg inhibited the ulcer lesion index by 70% and 74.6%, respectively. In the indomethacin-induced ulcer model, the extract (1000 mg/kg) inhibited the ulcer lesion index by 44%. Antiulcerogenic activity was also maintained in the ethanol-induced ulcer model with prior administration of indomethacin, inhibiting the ulcer lesion index by 70%. The results of this study suggest that the hydroalcoholic rosemary extract contains active substances that increase the content of non-protein sulfhydryl groups in the mucosa.