Introduction

Rosemary (Rosmarinus officinalis, now known as Salvia Rosmarinus) is a well known plant commonly found in gardens and parks around the world. Its strongly aromatic leaves and prolific flowers are a magnet to bees and other pollinating insects, and its traditional culinary applications are widely embraced.

Medicinal properties of rosemary are of course also substantial, and ancient texts extol many virtues.  In The Physicians of Myddfai, a compilation of medieval recipes written in the 13^th century at Myddfai in south Wales, it says of rosemary: “by washing each morning with the decoction and allowing it to dry naturally, the aged will retain a youthful look as long as they live”.

These appealing claims reflect rosemary’s antioxidant actions and multiple influences on cellular degradation and aging processes, and indicate the likely presence of other benefits when taken internally on a regular basis. In fact research is increasingly revealing its protective effects against many negative influences on health.

Protection against environmental toxins

Rosemary’s rich content of triterpene and other phenolic acid constituents such as rosmarinic, olenolic and ursolic acids contribute to its antioxidant and many antimicrobial activities. These help protect meat^{(1, 2)}, dairy products⁽³⁾, fish^(4,5) and other foods against spoilage and vegetable oils against oxidation⁽⁶⁾. Apart from being a flavour enricher, these are longstanding traditional uses.

Toxic compounds released or deposited within the soil, air or waterways by human activities are now being revealed by more and more science, as having harmful outcomes on living organisms and their environment.

Heavy metals such as cadmium and lead are amongst these, and are widely distributed in the environment as a result of mining and combustion emissions. Rosemary protects against liver damage due to both of these, and against kidney damage from lead exposure^{(7, 8)}. Addition of rosemary to fresh water reduces cadmium accumulation in the tissues of freshwater fish, and associated oxidative stress⁽⁹⁾. Washing fish in a rosemary solution, has been reported to reduce lead content⁽¹⁰⁾. Applications to remove lead from wastewater, have also been suggested⁽¹¹⁾.

Such protective actions against toxic environmental contaminants have recently been extended to a remediation ability for rosemary against accumulation of cadmium and lead in a busy urban environment.  Rosemary plants inoculated with a mycorrhizal fungus (Funneliformis mosseae) thrived in cadmium and lead contaminated soils, and mitigated urban traffic pollution in dense traffic conditions⁽¹²⁾.

Carnosic acid, another polyphenolic compound found in rosemary, shows a dose-related protective effect against neurotoxicity induced by dieldrin, an organochlorine pesticide implicated in neurological conditions such as Parkinson’s disease⁽¹³⁾.

Antispasmodic, anti-histaminic and anti-allergic actions on the respiratory tract, have recently been demonstrated for several rosemary constituents, including rosmarinic, carnosic and ursolic acids, rosmanol and carnosol⁽¹⁴). Airborne environmental pollutants are becoming increasingly linked with a diverse array of chronic health conditions in humans, and these actions are therefore relevant.

Given its many chemopreventive properties against harmful environmental toxins, it is hardly surprising that rosemary constituents such as rosmarinic and carnosic acids have demonstrated effective anti-proliferative properties against various cancers, and are the subject of research to develop new cancer treatments^{(15, 16)}. Potential synergistic effects with certain anti-cancer drugs, have also been suggested from in vitro and pre-clinical studies⁽¹⁷⁾.

Reducing harm from lifestyle factors

Many diets and lifestyles in the 21^st century are associated with conditions such as liver disorders, weight gain, cardiovascular disease and diabetes type 2. As such, plant-based interventions to help reduce some of the negative health impacts of a poor diet or sedentary lifestyle, and provide an element of prevention against these highly prevalent medical conditions, are of interest.

Many benefits were reported following administration of a rosemary extract to young rats feed a high fat western style diet⁽¹⁸⁾. These included reduced liver fat, liver cholesterol and triglycerides and increased plasma levels of HDL cholesterol.  Rats fed high doses of rosemary extract also had increased fasting plasma concentrations of Glucagon-like peptide-1 (GLP-1), suggesting possible benefits in weight management and diabetes. Modulation of the gut microbiota composition also occured.

Amelioration of the neurotoxic effects of the food flavour enhancer monosodium glutamate, has been reported in animal studies⁽¹⁹⁾.

The various pharmacological effects of rosemary and its key constituents, also  align well with a potential role in the management of metabolic syndrome, a constellation of complex coexisting cardiometabolic risk factors such as hyperglycemia, dyslipidemia, inflammation, abdominal obesity, vascular disorders and hypertension that raise the risk of diabetes mellitus and cardiovascular disease⁽²⁰⁾. Protection against nephropathy in diabetic rats, and enhancement of the nephroprotective effects of insulin, has been reported following supplementation with rosemary oil⁽²¹⁾.

Many studies have now shown hepatoprotective effects for rosemary^(22-24). A combination of rosemary with hawthorn protected against alcoholic liver disease, in a rat model⁽²⁵⁾.

Collectively, these studies suggest protective effects on several common conditions related to obesity, excess alcohol or poor diets.

Protecting male fertility

Declining human fertility is a growing concern in recent decades. While reasons for this are numerous, exposure to airborne pollutants and environmental toxins such as microplastics and nanoplastics and synthetic insecticides, are known contributory factors^{(26, 27)}.

Recent research showing that a forty five day pretreatment with rosemary leaf extract alleviated the damaging effects on the adrenal glands and testes following exposure to the synthetic pesticide cypermethrin, are promising. Restoration of spermatogenesis (sperm cell production) was also reported⁽²⁸⁾. Previous work found co-administration of rosemary with etoposide reduced the extent of testicular injury and DNA damage induced by this antineoplastic drug in male rats⁽²⁹⁾. These studies suggest a potential by rosemary to guard against infertility, as an outcome of chemotherapy or environmental toxin exposure.

References:

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