Introduction

With small, pointed leaves that are 2-4 cm in length, rosemary is a dense, evergreen, hardy, perennial herb that grows to a height of 60-200 cm. The leaves are resinous, with a dark green or blue upper surface and a white underside. The brown, square, and woody stems, are accompanied by stiff branches with cracked bark. Cymose inflorescence flowers are whitish, blue, or purple.¹ Native to the Mediterranean region, which stretches from Spain to the Balkans and into North Africa, is the rosemary (Rosmarinus officinalis L.), also known as the compass plant (Family Lamiaceae). It is widely grown in China, Spain, Morocco, Tunisia, France, Algeria, Portugal, and, to a lesser degree, Nilgiris and Bangalore in India.²

Humans have used rosemary, the memory herb of the mint family, since prehistoric times. Cuneiform records about the utilisation of rosemary can be found on Sumerian stone tablets dating back to the fifth millennium BC. The Greeks, who wore wreaths of rosemary in their hair, also believed that rosemary strengthened the brain and improved memory. The Chinese used rosemary as a health conditioner. The plant was interred in Egypt alongside the pharaohs. It is believed that Hungary water a rosemary infusion in spirits of wine was originally made for Queen Izabella of Hungary in 1235 to help heal her paralysed limbs. The word Rosmarinus originates from the Latin term rosmarinus, meaning "sea dew."³

Chemical composition of rosemary

The detailed content description of dried rosemary leaves is as follows: 5.7% moisture, 4.5% protein, 17.7% fat, 19.0% crude fibre, 47.4% carbohydrates, 6.0% ash, 1.5% calcium, 0.7% phosphorus, 0.03 % iron, 0.004% sodium, 1.0% potassium, 1.5% vitamin A, 0.75 IU/100 g, 0.51 mg/100 g vitamin B, and 61.3% vitamin C. The energy content is 440 calories/100 g. 1,8-cineol (15–20%), camphor (15–25%), borneol (16–20%), bornyl acetate (up to 7%), and α-pinene (25%) make up the majority of the oil.

Additional components include small amounts of β-pinene, linalool, camphene, subinene, myrcene, α-phellandrene, α-terpinene, limonene, p-cymene, terpinolene, thujene, copalene, terpinen-4-ol, α-terpineol, caryophyllene, methyl chavicol, and thymol. α-thujene, α-pinene, camphene, β-pinene, and 1,8-cineol make the majority of the first distillation fraction, while bornyl acetate and camphor make the majority of the second distillation.³ 

Depending on the growing location and/or additional factors like fertilisers, phenology, and source population, rosemary oil can vary in composition, both in terms of profile and percentage of each component.⁴

Mechanisms of action

Commercial products that use rosemary as an antioxidant in Europe and the USA. Antioxidative chemicals, like epirosmarinol, isopropanol, rosmaridiphenol, rosmariquinone, and rosmarinic acid, as well as carnosic acid, 12-methoxy carnosic acid, and carnosol, are the primary antioxidant components of rosemary. The scavenging of superoxide radicals, lipid antioxidation, metal chelating, and other processes are the reasons for rosemary's antioxidant qualities.⁵

Anti-inflammatory activity

It has been shown that rosemary extract inhibits the activation of NF-κB, a group of proteins vital for inflammation. By suppressing NF-κB pathways and lowering the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), R. officinalis exhibits anti-inflammatory properties.

The primary phenolic diterpenoid components of rosemary, carnosic acid and carnosol, have been shown to suppress the synthesis of nitric oxide (NO), with carnosic acid achieving this through the suppression of iNOS and COX-2 expression, lowering NO and TNF-α production.

Additionally, this prevents NF-κB from translocating to the nucleus. Further reducing inflammation. Similarly, carnosol inhibits both NF-κB and iNOS levels, further contributing to rosemary’s overall anti-inflammatory activity.⁶

Antioxidant activity

The antioxidant activity of rosemary is primarily attributed to phenolic diterpenes, which include isopropanol, carnosic acid, romano, epirosmanol, and carnosol. Strong antioxidant rosmanol inhibits the formation of superoxide anion and scavenges free radicals and lipid peroxidation.

The herb rosemary showed the greatest capacity to prevent lipid peroxidation. It has been demonstrated that the antioxidant properties of rosemary rely on the phenolic compounds that make up the plant's capacity to chelate metals and scavenge free radicals.⁷

Antimicrobial activity

Gomez-Estaca et al. discovered the common food-deteriorating bacteria inhibited by rosemary oil. Additionally, it has been shown that rosemary essential oil effectively inhibits Staphylococcus aureus, Bacillus cereus, and Escherichia coli, as well as Brochothrix thermosphacta and Enterobacteriaceae. 

The components of R. officinalis extract (RE) work synergistically by interacting with the bacterial cell membrane, disrupting essential cellular functions, such as electron transfer, fatty acid transport, genetic material production, and cellular component leakage.

Furthermore, it also resulted in a protein-membrane interaction that destroyed the structure and functionality of the membrane.⁸

Effect on gut microflora and growth

Gut microbial homeostasis is essential to an animal’s growth and maturation, influencing key physiological functions, such as the ability to digest nutrients, grow, produce, and fight off infections and oxidative stress. Under stressful conditions, RE has demonstrated the ability to modify gut microflora in mice, and rosemary leaf meal has been shown to boost Lactobacillus populations while lowering E. coli and Salmonella populations.⁹

Benefits of rosemary for digestive health

Rosemary is a traditional remedy for digestive issues such as indigestion and bloating. It may improve the symptoms of irritable bowel syndrome (IBS) and act as a muscle relaxant in the gastrointestinal (GI) tract.¹⁰

The skin and digestive tract both effectively absorb rosmarinic acid, a caffeic acid derivative found in rosemary. In human polymorphonuclear leukocytes, Rosemary inhibits the complement system and increases prostaglandin E₂ production while decreasing leukotriene B4 (LTB4) production.

Research suggests that rosmarinic acid and other constituents of rosemary may aid in the treatment or prevention of: 

• Bronchial asthma
• Spasmogenic disorders
• GI ailments (e.g. peptic ulcers, flatulence, dyspepsia, renal and biliary colic)¹¹
• Inflammatory diseases
• Hepatotoxicity
• Atherosclerosis
• Ischemic heart disease
• Cataracts
• Cancer
• Low sperm motility

Due to its anti-inflammatory properties, RE has shown efficacy in in vivo colitis models. Additionally, in vitro studies on RAW 267.4, macrophages demonstrated that lipopolysaccharide (LPS) stimulation alone significantly increased TNF-α, IL-6, and nitrite levels, whereas RE administration lowered these markers.

Furthermore, applying 5 and 10 μg/mL of RE reduced the nuclear translocation of the redox-sensitive transcription factor NF-κB, which reduced the expression of COX-2 and iNOS.¹²

Methods of consumption

Numerous ways thereby Rosemary is consumed are as follows.

Culinary applications

• Rosemary may be used as a seasoning for: soups, casseroles, salads, and stews.
• It also enhances flavour in meats such as chicken, game, lamb, hog, steaks, and fish, particularly oily varieties.
• It pairs well with grains, peas, potatoes, onions, mushrooms, and spinach. 

Medicinal uses and safety

When taken as directed, rosemary is generally regarded as safe. It is available in various forms, including:¹³

• Dried whole herb
• Dried powdered extract (in capsule form)
• Alcohol tinctures, teas, and liquid extracts made from fresh or dried leaves
• Volatile oil (for external use only)

For most individuals, Rosemary leaves (up to 8 weeks) are safe to use for short-term (up to 8 weeks). However, consuming large amounts of rosemary leaves or undiluted oil may induce sun sensitivity, nausea, and skin flushing.

Risks and precautions

• Allergy reactions have been reported on occasion
• Large amounts of rosemary leaves may lead to vomiting, spasms, seizures, coma, and in certain cases, pulmonary edema (fluid in the lungs) 
• Pregnant and nursing women should not take rosemary supplements as higher doses may cause miscarriage. However, culinary use is safe 
• Individuals with ulcerative colitis, Crohn's disease, high blood pressure, or ulcers should also avoid rosemary supplements 
• It is never advisable to take rosemary oil orally as it can be toxic if consumed¹⁴

Interaction with other medications

Rosemary may interact with several drugs including:

• Blood-thinning medications (aspirin, clopidogrel, and warfarin)
• Angiotensin-converting enzyme (ACE) inhibitors (captopril, enalapril, lisinopril, and fosinopril)
• Diuretics (hydrochlorothiazide and furosemide), increase the risk of dehydration
• Diabetes medications to alter blood sugar levels 

Due to its diuretic properties, rosemary may result in excessive water loss, and accumulation of lithium within the body, which can be harmful.¹⁵

Summary

In a nutshell, Rosemary is a herb that possesses a wide range of health benefits, attributed to its rich chemical constituents. It exhibits antimicrobial, anti-inflammatory, antioxidant, immune booster, cognitive and digestive health properties. It is beneficial to include a controlled amount of rosemary in the diet to seek benefits. However, precaution is necessary as excessive consumption of rosemary has certain side effects including vomiting, seizures, oedema, and spasms.  Pregnant individuals and those with underlying medical conditions should exercise caution due to drug interactions. Further research is needed to explore rosemary’s therapeutic potential and its unwinded benefits.