Garlic

Garlic is said to have favorable effects on several cardiac risk factors, including reduction of blood pressure and serum lipid and glucose levels; Garlic is said to have favorable effects on several cardiac risk factors, including reduction of blood pressure and serum lipid and glucose levels;garlic inhibits platelets in vitro. Garlic is also said to protect against laryngeal, gastric, colorectal, and endometrial cancer and adenomatous colorectal polyps. Garlic is also said to prevent the common cold and to treat nonalcoholic fatty liver disease (NAFLD). inhibits platelets in vitro. Garlic is also said to protect against laryngeal, gastric, colorectal, and endometrial cancer and adenomatous colorectal polyps. Garlic is also said to prevent the common cold and to treat nonalcoholic fatty liver disease (NAFLD).

Garlic has been evaluated in numerous studies for its effects on cardiovascular disease risk factors. A meta-analysis of 12 randomized trials found that garlic may have beneficial effects on high-density lipoproteins (HDL) and coronary artery calcification score (Garlic has been evaluated in numerous studies for its effects on cardiovascular disease risk factors. A meta-analysis of 12 randomized trials found that garlic may have beneficial effects on high-density lipoproteins (HDL) and coronary artery calcification score (1).

Some studies suggest that garlic supplementation lowers blood pressure, but the evidence is mixed. For example, a large meta-analysis of 20 trials (970 patients) of study duration ranging from 2 to 24 weeks found that patients taking a variety of Some studies suggest that garlic supplementation lowers blood pressure, but the evidence is mixed. For example, a large meta-analysis of 20 trials (970 patients) of study duration ranging from 2 to 24 weeks found that patients taking a variety ofgarlic preparations (eg, garlic powder, AGE) resulted in mean systolic and diastolic pressure decreases of 5.1 mm Hg and 2.5 mm Hg, respectively (2). Another meta-analysis of 12 randomized trials (553 hypertensive patients) lasting at least 2 months found a mean decrease of 8.3 mm Hg in systolic pressure and 5.5 mm Hg in diastolic pressure (3). However, other meta-analyses have reported no statistically significant blood pressure–lowering effects (1).

Results of the lipid-lowering effects of garlic supplementation have been inconsistent. A meta-analysis of 39 randomized studies (2298 participants) found that garlic lowered total cholesterol by 17 mg/dL (0.4 mmol/L) and LDL (low-density lipoprotein) cholesterol by 9 mg/dL (0.2 mmol/L) (4).

A 2015 meta-analysis of 7 studies (513 subjects) has verified the efficacy of garlic in lowering fasting glucose (5). A 2019 meta-analysis of 33 studies in 1273 subjects with diabetes found improvement in lipid parameters and fasting glucose, and a small decrease in hemoglobin A1C (6).

A randomized, placebo-controlled trial found that garlic can improve hepatic steatosis in patients with metabolic-dysfunction-associated steatotic liver disease (MASLD, previously called nonalcoholic fatty liver disease [NAFLD]), evidenced by changes in the ultrasound findings. Garlic also significantly decreased weight and liver enzymes (can improve hepatic steatosis in patients with metabolic-dysfunction-associated steatotic liver disease (MASLD, previously called nonalcoholic fatty liver disease [NAFLD]), evidenced by changes in the ultrasound findings. Garlic also significantly decreased weight and liver enzymes (7).

Scientific evidence of either garlic intake or garlic supplement use shows limited or no protection against cancer. A systematic review and meta-analysis evaluating garlic intake in relation to colorectal cancer incidence did not find any protective effect (8).

Garlic consumed in high doses appears to have general antimicrobial effects in vitro (Garlic consumed in high doses appears to have general antimicrobial effects in vitro (9). In a randomized trial, 146 participants were treated with an allicin-containing garlic supplement or placebo, one capsule a day, for 12 weeks. During the 12 weeks of the study, those treated with garlic had significantly fewer colds than the placebo group (24 versus 65, P < .001). The authors concluded that an allicin-containing garlic supplement can prevent attack by the common cold virus (10).

Most of these studies lack the specific details with regard to the supplement and/or concentration of active ingredients in the supplement, which may account for the variable results.

Breath and body smell and nausea may occur; high doses may cause burning in the mouth, esophagus, and stomach.

Theoretically, garlic is contraindicated in patients who have bleeding diatheses or who take antihypertensives, antiplatelet drugs, or warfarin. Garlic can reduce serum saquinavir levels. Garlic may interact with drugs that decrease blood sugar levels, causing possible hypoglycemia. (See also table is contraindicated in patients who have bleeding diatheses or who take antihypertensives, antiplatelet drugs, or warfarin. Garlic can reduce serum saquinavir levels. Garlic may interact with drugs that decrease blood sugar levels, causing possible hypoglycemia. (See also tableSome Possible Dietary Supplement–Medication Interactions.)

1. 1. Gadidala SK, Johny E, Thomas C, Nadella M, Undela K, Adela R. Effect of garlic extract on markers of lipid metabolism and inflammation in coronary artery disease (CAD) patients: A systematic review and meta-analysis. . Effect of garlic extract on markers of lipid metabolism and inflammation in coronary artery disease (CAD) patients: A systematic review and meta-analysis.Phytother Res. 2023 Jun;37(6):2242-2254. doi: 10.1002/ptr.7729

2. 2. Ried K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: an updated meta-analysis and review. J Nutr. 146(2):389S-396S, 2016. doi: 10.3945/jn.114.202192

3. 3. Ried K. Garlic lowers blood pressure in hypertensive subjects, improves arterial stiffness and gut microbiota: a review and meta-analysis. . Garlic lowers blood pressure in hypertensive subjects, improves arterial stiffness and gut microbiota: a review and meta-analysis.Exp Ther Med. 19(2):1472-1478, 2020. doi:10.3892/etm.2019.8374

4. 4. Ried K, Toben C, Fakler P. Effect of garlic on serum lipids: an updated meta-analysis. Nutr Rev .71(5):282-299, 2013. doi: 10.1111/nure.12012

5. 5. Hou LQ, Liu YH, Zhang YY. Garlic intake lowers fasting blood glucose: meta-analysis of randomized controlled trials. Asia Pac J Clin Nutr. 24(4):575-582, 2015. doi: 10.6133/apjcn.2015.24.4.15

6. 6. Shabani E, Sayemiri K, Mohammadpour M. The effect of garlic on lipid profile and glucose parameters in diabetic patients: A systematic review and meta-analysis. . The effect of garlic on lipid profile and glucose parameters in diabetic patients: A systematic review and meta-analysis.Prim Care Diabetes. 2019 Feb;13(1):28-42. doi: 10.1016/j.pcd.2018.07.007

7. 7. Soleimani D, Paknahad Z, Rouhani MH. Therapeutic effects of garlic on hepatic steatosis in nonalcoholic fatty liver disease patients: a randomized clinical trial. Diabetes Metab Syndr Obes. 13:2389-2397, 2020. doi:10.2147/DMSO.S254555

8. 8. Chiavarini M, Minelli L, Fabiani R. Garlic consumption and colorectal cancer risk in man: a systematic review and meta-analysis. Public Health Nutr. 19(2):308-317, 2016. doi: 10.1017/S1368980015001263

9. 9. Filocamo A, Nueno-Palop C, Bisignano C, et al.Effect of garlic powder on the growth of commensal bacteria from the gastrointestinal tract. Phytomedicine. 19(8-9):707-711, 2012. doi: 10.1016/j.phymed.2012.02.018

10. 10. Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Adv Ther. 18(4):189-193, 2001. doi:10.1007/BF02850113

The following English-language resource may be useful. Please note that The Manual is not responsible for the content of this resource.

1. National Institutes of Health (NIH), National Center for Complementary and Integrative Health: Garlic