Effects of garlic intake on cancer: a systematic review of randomized clinical trials and cohort studies

Jounghee Lee; Naisi Zhao; Zhuxuan Fu; Jihee Choi; Hae-Jeung Lee; Mei Chung

doi:10.4162/nrp.2021.15.6.773

Effects of garlic intake on cancer: a systematic review of randomized clinical trials and cohort studies

Nutr Res Pract. 2021 Dec;15(6):773-788. doi: 10.4162/nrp.2021.15.6.773. Epub 2021 Jul 26.

Authors

Jounghee Lee¹, Naisi Zhao², Zhuxuan Fu³, Jihee Choi⁴, Hae-Jeung Lee⁴, Mei Chung^{2

5}

Affiliations

¹ Department of Food and Nutrition, Kunsan National University, Gunsan 54150, Korea.
² Department of Public Health and Community Medicine, School of Medicine, Tufts University, Boston, MA 02111, USA.
³ Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA 15261, USA.
⁴ Department of Food and Nutrition, Gachon University, Seongnam 13120, Korea.
⁵ Division of Nutrition Epidemiology and Data Science, Freidman School of Nutrition Science and Policy, Tufts University, Boston, MA 02111, USA.

Abstract

Background/objectives: Due to the rapid increase of global cancer incidence and mortality and a high level of interest in cancer prevention, a systematic review of garlic intake and cancer risk is needed.

Subjects/methods: We implemented a systematic review to examine the effects of varying levels of garlic intake on cancer. We conducted comprehensive literature searches in three electronic databases (MEDLINE, Embase, and Web of Science) for studies published between database inception and July or September of 2018. Two investigators independently screened abstracts and full-texts, extracted data, and assessed risk of bias (RoB). A total of one medium-quality randomized controlled trial (RCT) and 13 cohort studies graded as high RoB were included.

Results: The 1-year follow-up results from a RCT showed that a significant decrease in the number and size of colorectal adenomas among participants with colorectal adenomas who received high-dose aged garlic extract (AGE) compared with those who received low-dose AGE (P < 0.05). The results of prospective observational studies provided inconsistent associations of colorectal cancer risk with garlic supplements and garlic intake as food.

Conclusions: In summary, the AGE was effective in reducing the number and magnitude of colorectal adenomas in one RCT, but there were inconsistent associations between garlic intake and colorectal cancer in cohort studies. Therefore, we could not draw a firm conclusion regarding the effects of garlic on cancer, because the current strength of evidence is inadequate due to a lack of number of high-quality RCTs.

Keywords: Garlic; cancer; systematic review.