Boost Immune Function with Garlic

 

    The outbreak of coronavirus in China reminded us how important it is to have a good immune system to fend ourselves from unpredictable viral infections. Someone shared online that he had long-lingered fever and coughing which made him worried that he might have caught the coronavirus. After he used a folk remedy of eating a large dose of garlic, the symptoms disappeared overnight. While sharing this anecdotal report in our nutrition-and-health discussion group, one of the members said that she had used a similar garlic cure for cold and flu successfully for many years.

 

    Indeed garlic had been suggested as a promising candidate for maintaining the homeostasis of the immune system (1). Garlic has immune-modulating effects by increasing macrophage activity, natural killer cells, and the production of T and B cells. In vitro and cell culture studies showed garlic to have antibacterial, antivirus, antifungal, and antiparasitic properties. Clinical trials have shown garlic to significantly reduce the number, duration, and severity of upper respiratory infections (2).

 

    A randomized, double-blind, placebo-controlled trial in 146 participants (n=73 per group) testing the effect of a daily garlic supplement over 3 month found a 37% fewer numbers of colds (24 vs 65; p< 0.001) and a 30% reduction in the duration of illness (1.52 vs 5.01 days; p < 0.001) in the group taking garlic compared with the placebo group. During the study, the 16 volunteers taking the placebo became reinfected (experienced more than one cold) and only 2 volunteers taking the active supplement had reinfection. Volunteers in the garlic group were less likely to get a cold and recovered faster if infected. Volunteers taking placebo were much more likely to get more than one cold over the treatment period (3).

 

    A randomized, double-blind, placebo-controlled parallel intervention study recruited 120 healthy subjects (n=60 per group) to determine the effect of aged garlic extract supplementation (2.56 g/day) on immune cell proliferation and cold and flu symptoms. Aged garlic extract was produced by a unique aging process that garlic can be rendered nearly odorless, due to the conversion of strong organosulfur compounds into water-soluble compounds such as S-allyl-L-cysteine and S-allylmercaptocysteine (4).

 

    After 45 days of consuming aged garlic extract, gamma-delta-T cells and natural killer cells in the garlic group were shown to proliferate significantly better compared to placebo with 8-fold increase in gamma-delta-T cells (p = 0.039) and 2-fold increase in natural killer cells (p = 0.043) proliferation in the garlic group. Innate immune cells, such as natural killer cells and monocyte/macrophages, respond to pathogen-associated molecular patterns (PAMP) via their pattern recognition receptors. While T cells are not considered part of the innate immune system, gamma-delta-T cells are a unique T cell in that they have been shown to respond to PAMP. When a pathogen is present, the innate cell senses the molecular pattern and initiates a response. The proliferation of immune cells is an index of the cell’s potential. If proliferation is increased after consuming a bioactive compound then that cell type most likely has a greater pathogen fighting ability when called upon in vivo. Each of these cell types kills virally infected host cells, and the enhancement of their functions by consuming aged garlic extract may have contributed to the reduced severity of illness (4).

 

    After 90 days of supplementation, illness diary entries showed that the incidence of colds and flu were not statistically different. However, the group consuming the aged garlic extract had reduced severity as noted by a reduction in the number of symptoms reported (21% fewer, p < 0.001), a reduction in the number of days (61% fewer, 53 vs 126 days; p < 0.001), and a reduction of the number of work/school days missed due to illness where the subjects functioned sub-optimally (58% fewer, p= 0.035) (4).

 

    Besides, garlic contains immunomodulatory proteins garlic lectins ASA I and ASA II. The immunogenicity of garlic lectins upon feeding in BALB/c mice showed a remarkable humoral immune response compared to control. The lectin-specific serum IgG response was comparable to the oral immunogen, phytohemagglutinin (5). 

 

    Garlic is one of the most employed seasonings for cooking, commonly used in healthy diets such as the Mediterranean diet. Garlic is also one of the favorite foods for my 103-year-old grandma which may be one of the reasons why she has a long and healthy life. I have shared the nutrition secrets from my grandma previously if you are interested in learning more (https://www.calnutritiongroup.com/post/healthy-aging-nutrition-tips-from-my-102-year-old-grandma).  Garlic has immune-modulating properties. We can eat more garlic to boost our immune system against diseases.

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References:

1. Arreola R, Quintero-Fabián S, López-Roa RI, Flores-Gutiérrez EO, Reyes-Grajeda JP, Carrera-Quintanar L, Ortuño-Sahagún D. Immunomodulation and anti-inflammatory effects of garlic compounds. J Immunol Res. 2015;2015:401630.

2. Ried K. Garlic Lowers Blood Pressure in Hypertensive Individuals, Regulates Serum Cholesterol, and Stimulates Immunity: An Updated Meta-analysis and Review. J Nutr. 2016;146(2):389S-396S.

3. Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Adv Ther 2001;18:189–93.

4. Nantz MP, Rowe CA, Muller CE, Creasy RA, Stanilka JM, Percival SS. Supplementation with aged garlic extract improves both NK and gd-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clin Nutr 2012;31:337–44.

5. Clement F, Venkatesh YP. Dietary garlic (Allium sativum) lectins, ASA I and ASA II, are highly stable and immunogenic. Int Immunopharmacol. 2010;10(10):1161-9.