Garlic

The garlic's scientific name is Allium sativum L. (Liliaceae)¹. It can also be found as camphor of the poor, nectar of the gods, majo, poor's molasses, rustic molasses, smelly rose². However, the common name by which it is known in Costa Rica is garlic. The bulb is used for medicinal effects. Alliin and allicin are usually used as active ingredients in different formulations¹.

Garlic is one of the oldest medicinal foods and one of the most researched plants in the world. Due to its wide recognition and cultivation, there is little chance of adulteration with other species. However, garlic used in dietary supplements is handled more carefully than garlic used in commodity spices, it is to preserve the activity of allinase, and subsequently, allicin performance since allinase is sensitive to heat and bruise decomposition³. Likewise, garlic has a strong smell and a pungent flavor that characterizes it².

Garlic is a herbaceous plant with bulbs composed of numerous fibers divided and wrapped in whitish skin. In addition, it contains 4-6 segments with a characteristic spicy flavor. This perennial herb has a cylindrical stem 50 cm high and sparse, flat leaves 2-3 cm wide. It has sparse flowers in a lilac / pink corsage, and in some cases, the flowers are replaced by bulbs^1,4. It should be noted that the flowers are rarely open and can wilt in the bud. The flowers are on thin pedicels, consisting of six-segment perianth approximately 4-6 mm long. The fruit is a small loculicidal capsule, and the seeds are rarely produced².

Garlic is from Siberia and was domesticated in Central Asia. Nomadic tribes have spread it, as it has been cultivated and used in all cultures for more than 5,000 years. It was introduced in America in the XV century¹.

Garlic is grown in loose, rich, silty-sandy, humid, deep, drained soil; mountainous areas with the temperate or cold climate at 1,000-2,400 meters above sea level. It is propagated by bulbils that are sown in full sun; requires abundant water and fertilization. As they mature, the bulbs are dug up and stored in a cool, ventilated place, often cured with smoke that decreases weight loss and partially inhibits germination; teeth become dehydrated ground or flaked¹.

Taxonomy⁵

Kingdom: Plantae

Subkingdom: Viridiplantae

Infrakingdom: Streptophyta

Division: Tracheophyta

Subdivision: Spermatophytin

Class: Magnoliopsida

Superorder: Lilianae

Order: Aspargales

Family: Amaryllidaceae

Gender: Allium

Species: A. sativum

Composition

Allium savitum bulb contains sulfur compounds such as ajoene and derivatives, allicin, allyl-methyl trisulfide and derivatives, clicoaliin and derivatives, diallyl disulfide and derivatives, dimethyl sulfide, allyl-methyl disulfide and derivatives, dimethyl thiosulfonate and derivatives, amino acids derived from cysteine and anthocyanins, sulphurated amino acids: alliin (by enzymatic oxidation it becomes allicin, intermediate in the formation of allyl disulfide derivatives, final constituents of essential oil), 5-butyl-cysteine sulfoxide and derivatives, lipids such as cerebrosides, steroids, prostaglandin A, B, E, and F; alkaloids such as phosphatidylcholine, nicotinic acid, diterpenes (gibberellin A-3 and A-7); carbohydrates such as allium fructans; saponins: derivatives of erubioside, sativoside, and tigonine⁴.

Now, from 100 g of bulb (117 kcal), you will find: 67.8% water, 3.5% protein, 0.3% fat, 27.4% carbohydrates, 0.7% fiber, 1% ash, 18 mg calcium, 88 mg phosphorus, 1.5 mg iron, 18 mg sodium, 373 mg potassium, 0.24 mg thiamine, 0.05 mg riboflavin, 0.4 mg niacin, and 10 mg ascorbic acid⁴.

It should be noted that the antimicrobial activity is attributed to alliin, a sulfoxide that by alliinase action is converted to allicin and allyl and ajoene disulfide. Antimicrobial activity is also attributed to alixin and garlicin that are obtained by severe bulb treatments. Ajoene is an antithrombotic factor whose action involves fibrinogen receptors on platelets and prevents platelet aggregation; It reduces arachidonate metabolism by inhibiting the enzymes' prostaglandin synthetase and 5-lipoxygenase and has shown a promising role in the treatment of leukemia. Fructosans inhibit adenosine deaminase by participating in the regulation of the processes in which adenosine is involved¹.

Traditional use

Garlic has been used as herbal medicine to treat asthma, bronchitis, influenza, and colds¹. Besides, it serves as a treatment for respiratory infections². It is commonly used to treat bronchopulmonary diseases as expectorant antiseptic and asthma. Likewise, it is used as a hypotensive, diaphoretic, and vermifuge⁶.

The most commonly used form of garlic extraction is maceration⁷. There are several variants to this method, depending on the amount of plant material and the concentration of the extract required, however, all methods of this type have in common that the extraction solvent can be water (aqueous extract), alcohol (ethanolic extract) or a hydroalcoholic combination.

One way of making the macerated garlic extract is by using the garlic bulb (bulb extract) since these are the parts of the garlic with the highest biological activity. For the preparation, the garlic is peeled, cut into slices, and stored for 40 days at a temperature of 60-70°C, then suspended in a hydroalcoholic solution. After this time, the processed garlic is suspended in an anaerobic maceration for 18 weeks, at the end of which period they are filtered and rotavaporated; the liquid extract obtained should be kept refrigerated⁸. Another way to make this liquid extract is in cold in a conical flask for 72 hours⁷.

Spray drying is another way of making garlic extracts, this technique is performed on the liquid extracts, to obtain a dry extract in a solid matter form. It consists of atomizing it in the form of small drops in a dry medium, dehydrating it employing hot air, and turning it into powder or tiny spheres⁷.

Toxicology

Studies carried out found that the LD50 of the bulb by oral and subcutaneous route to rats of both sexes was higher than 30 mL/kg. The aqueous extract from the bulb elicited in vitro uterotonic activity on the pregnant female mouse's uterus. Furthermore, the bulb extract (2g/kg) administered in rats five times a week for six months showed no toxic effects. Externally, poultices with high concentrations of bulb extract can cause skin necrosis and allergenic activity. The latter has been verified with the internal administration of the aqueous extract orally in rats and sensitive humans⁴.

Similarly, the oral bulb can irritate the urinary tract in people with specific sensitivity. A dose of 350 mg/person (both sexes from 30 to 62 years old) administered twice a day did not produce toxic manifestations. No information evidences the safety of its medicinal use in children, pregnancy, or lactation⁴.

In another study, it was shown that the ethanolic extract is not mutagenic in S. typhimurium. The LD50 of mouse allicin is 60 mg/kg IV and 120 mg/kg SC; the LD50 of the oil is 50-78 mg/kg IV; the LD50 of neoalicin is 70 mg/kg IV and 600 mg/kg orally. Oral administration is not genotoxic by testing the micronucleus in the bone marrow and inducing changes in sister chromatids in spermatogonia. Due to prolonged traditional use, daily consumption does not pose any health risk¹.

Contraindications

Conditions and diseases such as hyperthyroidism, active bleeding and, thrombocytopenia are contraindicated. Do not prescribe the oil during pregnancy¹. It is contraindicated in patients with a known garlic allergy. Besides, other contraindications include acquired immunodeficiency syndrome (AIDS), surgery, and diabetes mellitus⁹.

Until more data becomes available, people with diabetes mellitus have to be careful when taking dietary supplements containing garlic and follow their normally recommended blood glucose control strategies. Because garlic components inhibit platelet aggregation, care must be taken in patients receiving anticoagulant or thrombolytic therapy⁹. Despite this, garlic's safety level is reflected in its worldwide use as a condiment in food².

Warnings

The juice and oil irritate the mucosa and the conjunctiva¹. Additionally, consuming large amounts of garlic can increase the risk of postoperative bleeding. Also, ingesting fresh garlic bulbs, extracts, or oil on an empty stomach can cause heartburn, nausea, vomiting, and diarrhea².

Side effects

Case reports have highlighted the possibility that the use of garlic may cause allergic reactions (allergic contact dermatitis, generalized urticaria, angioedema, pemphigus, anaphylaxis, and photoallergy), impaired platelet function, and clotting (with a possible risk of bleeding)^10,11) and burns (when fresh garlic is applied to the skin, particularly under occlusion dressings). It should be noted that garlic can cause bad breath or body odor, so many people decide not to consume it¹⁰. The oral bulb can irritate the urinary tract in people with specific sensitivity⁴. Furthermore, the use of garlic in some cases evokes asthmatic attacks after inhalation of the drug powder².

The most common effects associated with the use of garlic in therapeutic doses are mild gastrointestinal, such as nausea, bloating, flatulence, dyspepsia, nausea, vomiting, diarrhea, and pyrosis. Severe gastrointestinal adverse effects can also be found, such as small bowel obstruction, epigastric and esophageal pain, hematemesis, and hematochezia. It can also cause hypotensive effects, heart attack, and Meniere's disease¹⁰.

Pregnancy and lactation

Garlic is safe during pregnancy in amounts that are generally eaten in food. However, garlic supplements or large amounts of garlic should be avoided during pregnancy due to a possible increased risk of bleeding or stimulation of uterine contractions¹². During lactation, there are no known contraindications. The excretion of the components of garlic in breast milk and its effect on the newborn has not been established².

Interactions with other drugs

Garlic causes a harmful effect related to kidney damage and nephrotoxicity combined with statins¹³. Clinical evidence suggests that taking garlic may result in pharmacokinetics or pharmacodynamic interactions that could represent a potential risk to patients taking conventional medications, particularly in subjects treated with anticoagulants. Blood clotting time has been reported to double for patients taking warfarin and garlic supplements¹⁰.

Additionally, interactions with antiretroviral therapies may occur. A severe drug interaction has been reported between garlic and an HIV protease inhibitor, saquinavir; this interaction may compromise antiretroviral therapy's effectiveness and lead to higher drug resistance rates against the acquired immunodeficiency virus. Other conventional medications that could interact with garlic include the antidiabetic chlorpropamide and the pain reliever paracetamol¹⁰.

Dosage and administration

Studies report the use of 4-12.3 mg/day of garlic oil orally.

Adults: The World Health Organization (WHO) recommends 2 to 5 grams of fresh garlic, 0.4 to 1.2g of dry powder, 2 to 5 mg of oil, 300 to 1,000 mg of extract, equivalent to 2- 5 mg allicin/day.

6-10 mg alliin (approx. 3-5 mg allicin) daily, typically contained in one clove of garlic or 0.5-1.0 g of dry garlic powder⁶.

2 to 4 grams of the dry bulb or 2 to 4 milliliters of tincture (1:5 dilution in 45% ethanol) orally three times a day for upper respiratory tract infections⁶.

Pediatrics: dry extract is recommended as a single dose (100 - 200 mg) once or twice a day. The daily dose is 100-400 mg. The herbal substance powder or the liquid extract of garlic is not recommended in children and adolescents under 18 years of age¹⁴.

Geriatric: liquid extract is recommended as a single dose (110 - 220 mg) 4 times a day. The daily dose is 440 - 880 mg. The dry extract is recommended as a single dose (100 - 200 mg) once or twice a day. The daily dose is 100 - 400 mg¹⁴.

Preclinical Studies

Garlic is well-known for improving the immune system. A preclinical study was done to examine the protein fraction changes during garlic aging and identify immunomodulatory proteins. The modifications that occur in garlic during the aging process were studied by protein quantification and gel electrophoresis. Purification and identification of immunomodulatory proteins have been achieved by Q-Sepharose chromatography and mitogenic activity. In the study, only two main proteins (range of 12-14 kDa by SDS-PAGE) were observed in aged garlic extract (AGE). The purified protein components QA-1, QA-2, and QA-3, showed immunomodulatory and mannose-binding activity; QA-2 showed the highest mitogenic activity. The QA-2 and QA-1 proteins' identity with the ASA I and ASA II garlic lectins, respectively, was confirmed by hemagglutination analysis. QA-3 exhibited mitogenic activity but not hemagglutination activity¹⁵.

Another study was done on the enteric-coated garlic supplement, which is a kind of garlic preparation based on garlic oil and garlic powder compressed in tablets, with a remarkable improvement in normal mice's immunocompetence. In the study, garlic oil was extracted from the fresh garlic bulb by steam distillation and complexed with 2-hydroxypropyl-beta-cyclodextrin using a method of high-energy ball milling to then incorporate the inclusion complex with enteric-coated powder and reduce its gastrointestinal irritant. Based on the maximum tolerance dose test, mice that took an enteric-coated garlic tablet by gavage at a dose of 3 g/kg body weight did not show symptoms of acute toxicity¹⁶.

In this study, experimental animals were randomly assigned. Different doses of garlic tablets for 30 consecutive days were given orally. Furthermore, their immune functions were comprehensively analyzed. Compared to the control, the garlic tablet significantly improved ConA-induced splenic lymphocyte proliferation, serum hemolysin production, the number of hemolytic pest-forming cells, peritoneal macrophages phagocytic activity, and the rate of carbon removal at the dose of 400, 600 mg/kg of body weight. It also improved the DNFB-induced delayed-type hypersensitivity reaction and NK cells' cytotoxicity at the 600 mg/kg body weight dose. In addition, garlic tablets increased serum cytokine secretion (TNF-α, IL-2) in a dose-dependent manner¹⁶.

A study was conducted to evaluate the inhibitory effects of garlic extract on avian infectious bronchitis virus. For this purpose, four groups of chick embryonic eggs were used, where the first group was used for virus titration; the second group was given the mixture of different titrations of virus and garlic extract; the third group received a virus titration and after 8 hours received garlic extract and the last group received different dilutions of garlic extract. According to the results of the study, it was shown that garlic extract influences the garlic virus in the replication phase. In addition, avian infectious bronchitis virus RNA and virus replication were dose-dependently decreased¹⁷.

A preclinical study hypothesized that allicin can alleviate immune dysfunction caused by the reticuloendotheliosis virus (REV). For this purpose, 240 White Leghorn SPF chickens were used and divided into 5 treatment groups and one control group. It was found that treatment with allicin enhanced the proliferation of lymphocytes infected with this virus, demonstrating that allicin helps to alleviate the growth inhibition induced by REV infection and immune system dysfunction. In addition, it was shown that in the groups treated with allicin, the expression of inflammatory cytokines produced by REV infection was decreased. It was also found that allicin significantly reduced the oxidative stress caused by REV infection¹⁸.

In a preclinical study, the effect of the 14 kDa protein isolated from AGE on the maturation and immunomodulatory activity of dendritic cells (DC) was studied to prove its immunomodulatory effects. Biochemical methods were used to purify the AGE protein; the semi-purified 14 kDa protein was run on gel filtration Sephadex G50 and checked for purity by SDS-PAGE. DC was separated from the spleen of BALB / c mice by Nycodenz centrifugation and adhesion to plastic plates. The 14 kDa AGE protein was added to the overnight culture of the DC medium and the expression percentages of CD40, CD86, and MHCII were evaluated by flow cytometric analysis. In addition, T-cell proliferation was measured by the mixed allogeneic lymphocyte reaction (MLR) test. Despite the results, more research has to be done to conclude if the 14 kDa protein isolated from AGE induces DC maturation and increases immunostimulatory activity¹⁹.

On the other hand, an in vivo study carried out with Wistar rats evaluated the effects of garlic oil on the serum levels of IFN-у, TNF-α, and IL-5. Obtaining as a result that the garlic oil increased the levels of IFN-у and TNF-α to 2 and 3 times those of the control group (which were only treated with corn oil) respectively. It also produced a slight increase in IL-5 levels. In addition, the effect of this oil on IgG and IgM levels was determined, where an increase of approximately 60% in IgG levels was obtained as a result, but a significant increase in IgM levels was not registered²⁰.

Similarly, the effect of garlic oil on mRNA expression levels in interleukins 2, 4, and 5 in rat leukocytes was evaluated and it was determined that it decreases the expression levels of these interleukins in contrast to the control group²⁰.

Clinical Studies

A study at the University of Florida recruited 120 healthy subjects (60 per group) to determine the effect of consuming supplements with AGE (2.56 g/d) on immune cell proliferation and cold symptoms, and flu. After 45 days of AGE consumption, γδ-T and NK (natural killer) cells thrived better and were more activated than cells in the placebo group²¹. After 90 days, the AGE group showed a reduction in the severity of the cold and flu, a reduction in the number of symptoms, the number of days the participants functioned suboptimally, and the number of days of work school missed^22,23.

Moreover, a clinical study evaluated the effects of allicor, a long-acting garlic tablets, on acute respiratory viral infection incidence in children. For the first stage, allicor tolerance (600 mg/day) and its effects on ARD morbidity were investigated in a 5-month open study in 172 children and adolescents aged 7 to 16, compared to 468 individuals in a control group; however, this was not observed to induce gastrointestinal side effects in children at any dose, while ARD morbidity was reduced 2 to 4-fold compared to controls. In the second stage, allicor (300 mg/day) effects on morbidity from ASRD were investigated in a 5-month, double-blind, randomized, placebo-controlled trial. This study included 42 children aged 10-12, compared to 41 placebo-treated children and 73 children treated with benzimidazole. For this stage, allicor reduced ARD morbidity 1.7 times compared to placebo and 2.4 times compared to benzimidazole. Furthermore, there was no significant difference in ARD morbidity between the placebo and benzimidazole groups²⁴.

Similarly, a clinical trial regarding the prevention of the common cold was performed with a garlic supplement. A sample of 146 people was used; there were two groups, volunteers who were going to receive a placebo; and the second group of participants received a garlic-containing supplement (allicin) for 12 weeks. The researchers used a five-point scale to assess their health and recorded all infections and symptoms of the common cold²⁵.

Through a clinical study, the effect of garlic (Allium sativum) on the gene expression of pro and anti-inflammatory cytokines was evaluated, for which peripheral blood mononuclear cells (PBMC) from donors in optimal health conditions were treated. Treatment with garlic provided satisfactory results since it significantly stimulated the expression of said cytokine in 4 of the 6 study participants. In these donors, an increase in IL-17 transcription was detected thanks to the treatment with garlic²⁶.