What is the mechanism by which Allium sativum (garlic) exerts its potential immunomodulatory effects in the prevention or treatment of the common cold, also known as upper respiratory tract infection (URTI)?

From the Guidelines

Garlic may help reduce the severity and duration of common cold symptoms due to its antimicrobial and immune-boosting properties, but the current evidence is limited and not directly addressed in the provided studies. The provided study 1 focuses on various treatments for the common cold, including vitamin C, antibiotics, nasal corticosteroids, probiotics, antihistamines, decongestants, paracetamol, NSAIDs, and zinc lozenges, but does not specifically discuss the effects of garlic. However, based on general knowledge of garlic's active compound, allicin, it is believed to have immune-boosting properties that may help fight viral infections and stimulate the immune system to combat cold viruses more effectively. Some key points to consider when using garlic to potentially help with common cold symptoms include:

• Consuming 2-3 cloves of raw garlic daily or taking a garlic supplement containing allicin when you feel a cold coming on may be beneficial
• Garlic is not a cure for the common cold and should be used as a complementary approach alongside rest, hydration, and over-the-counter cold remedies if needed
• Raw garlic can cause digestive discomfort in some people, so start with small amounts
• Garlic supplements are an alternative if you dislike the taste or smell of fresh garlic
• While promising, more research is needed to conclusively prove garlic's effectiveness against colds, and its potential benefits are likely modest, but it's generally safe for most people when consumed in normal dietary amounts.

From the Research

Mechanism of Immunomodulatory Effects of Allium sativum (Garlic)

The potential immunomodulatory effects of Allium sativum (garlic) in the prevention or treatment of the common cold, also known as upper respiratory tract infection (URTI), can be attributed to its alleged antimicrobial and antiviral properties 2, 3, 4.

Key Findings

• A single trial suggested that garlic may prevent occurrences of the common cold, with 24 occurrences in the garlic intervention group compared to 65 in the placebo group (P < 0.001) 2, 3, 4.
• The number of days of illness was lower in the garlic group compared to the placebo group (111 versus 366) 2, 3, 4.
• Adverse effects of garlic supplementation included rash and odor 2, 3, 4.

Limitations of Current Evidence

• There is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold 2, 3, 4, 5.
• Claims of effectiveness appear to rely largely on poor-quality evidence 2, 3, 4.
• Further studies are needed to validate the potential benefits of garlic in preventing or treating the common cold 2, 3, 4, 5.

Comparison with Other Nutrients

• Other nutrients, such as vitamin C, vitamin D, zinc, and Echinacea, have also been found to have immunomodulatory effects and may be beneficial in preventing or treating the common cold 6.
• Vitamin C supplementation has been shown to reduce the duration and severity of common colds 6.
• Zinc supplementation may shorten the duration of colds by approximately 33% 6.
• Vitamin D supplementation has been found to protect against common colds, particularly in individuals with vitamin D deficiency 6.
• Echinacea prophylactic treatment has appeared to be beneficial for preventing/treating common colds 6.