Several observational studies suggest that consumption of allium vegetables may help in reducing the risk of different types of cancers. Both onion and garlic may help in reducing the risk of gastric cancer and colorectal cancer. Garlic may also help in reducing the risk of breast, prostate, lung, gastric, esophageal and liver cancers, but not distal colon cancer. While onions are also good for handling hyperglycemia (high blood glucose) and insulin resistance in breast cancer patients, they may not have any significant effect on prostate cancer risk, and cooked onions may even increase the risk of breast cancer.
What are Allium Vegetables?
Allium vegetables have been a part of almost all types of cuisines. In fact, it is difficult to imagine preparing a meal without including allium vegetables. The term “Allium” may sound alien to many of us, however, once we get to know the vegetables included in this category, we will all agree that we have been using these tasty bulbs in our daily diet, both for flavor as well as for nutrition.
“Allium” is a Latin word which means garlic.
However, apart from garlic, allium vegetables also include onion, scallion, shallot, leek and chives. Though some of the allium vegetables make us cry while chopping, they provide great flavor and aroma to our dishes and are also rich in beneficial sulfur compounds which provide great health benefits including antioxidant, antiviral, and antibacterial properties. They are also considered to have anti-inflammatory, immune-boosting and anti-aging properties.
Nutritional Value of Allium Vegetables
Most of the allium vegetables contain organo-sulphur compounds as well as different vitamins, minerals and flavonoids such as quercetin.
Allium vegetables such as onion and garlic contain different vitamins such as Vitamin B1, Vitamin B2, Vitamin B3, Vitamin B6, folic acid, Vitamin B12, Vitamins C and minerals such as iron, magnesium, phosphorus, potassium, sodium and zinc. They also contain proteins, carbohydrates and dietary fiber.
Association between Allium Vegetables and the Risk of Different Types of Cancers
In the last two decades, different observational studies were focused on the anticarcinogenic potential of allium vegetables. Researchers across the world have carried out studies to evaluate the association between different allium vegetables and the risk of different types of cancers. Examples of some of these studies are elaborated below.
Association between Allium Vegetables and Breast Cancer Risk
A study done by the researchers of Tabriz University of Medical Sciences, Iran evaluated dietary allium vegetable consumption and the risk of breast cancer among Iranian women. The study used food frequency questionnaire based data from 285 breast cancer women in Tabriz, northwest Iran, who were aged between 25 and 65 years old and age- and regional-matched hospital based-controls. (Ali Pourzand et al, J Breast Cancer., 2016)
The study found that a high consumption of garlic and leek may reduce the risk of breast cancer. However, the study also found that a high consumption of cooked onion may be associated with an increased risk of breast cancer.
Impact of Yellow Onion on Hyperglycemia (high blood glucose) and Insulin Resistance in Breast Cancer Patients
Another clinical trial conducted by the researchers of Tabriz University of Medical Sciences, Iran evaluated the impact of eating fresh yellow onions on insulin-related indices compared with a low-onion-containing diet among breast cancer patients who were undergoing treatment with doxorubicin. The study included 56 breast cancer patients who were aged between 30 and 63 years.After the second cycle of chemotherapy, the patients were randomly divided into 2 groups- 28 patients supplemented with 100 to 160 g/d of onions, referred to as the high onion group and another 28 patients with 30 to 40 g/d small onions, referred as the low onion group, for 8 weeks. Out of these, 23 cases were available for analysis.(Farnaz Jafarpour-Sadegh et al, Integr Cancer Ther., 2017)
The study found that those with a high daily onion intake may have a significant decrease in the serum fasting blood glucose and insulin levels as compared to those taking low amounts of onion.
Allium Vegetables and Risk of Prostate Cancer
- A study published by the researchers of China-Japan Friendship Hospital, China, evaluated the association between allium vegetable intake and risk of prostate cancer. Data for the study was obtained through a systematic literature search up to May 2013 in PubMed, EMBASE, Scopus, Web of Science, Cochrane register, and Chinese National Knowledge Infrastructure (CNKI) databases. A total of six case-control and three cohort studies were included. The study found that garlic intake significantly decreased the risk of prostate cancer, however, significant associations were not observed for onions. (Xiao-Feng Zhou et al, Asian Pac J Cancer Prev., 2013)
- A study published by researchers in China and the United States evaluated the association between intake of allium vegetables, including garlic, scallions, onions, chives, and leeks, and the risk of prostate cancer. Data was obtained from face-to-face interviews to collect information on 122 food items from 238 prostate cancer patients and 471 male controls. The study found that men with highest intake of total allium vegetables (>10.0 g/day) had a significantly lower risk of prostate cancer compared to those with lowest intake (<2.2 g/day). The study also found that the reduction in risk was significant in the highest intake categories for garlic and scallions. (Ann W Hsing et al, J Natl Cancer Inst., 2002)
Raw Garlic Consumption and Risk of Liver Cancer
In a population based case-control study in Eastern China between 2003 to 2010, the researchers evaluated the association between raw garlic consumption and liver cancer. Data for the study was obtained from interviews with 2011 liver cancer cases and 7933 randomly selected population-controls.(Xing Liu et al, Nutrients., 2019)
The study found that eating raw garlic twice or more per week may be associated with a reduced risk of liver cancer. The study also found that high intake of raw garlic may decrease the risk of liver cancer among Hepatitis B surface antigen (HBsAg) negative individuals, frequent alcohol drinkers, those having history of eating mold-contaminated food or drinking raw water, and those without family history of liver cancer.
Association of Allium Vegetables with Colorectal Cancer
- A hospital-based study between June 2009 and November 2011, done by researchers of the Hospital of China Medical University, China, evaluated the association between the intake of allium vegetables and colorectal cancer (CRC) risk. The study included data from 833 CRC cases and 833 controls whose frequency was matched by age, sex, and residence area (rural/urban) with that of the CRC cases.The study found a decreased CRC risk in both men and women with a high consumption of total and several individual allium vegetables including garlic, garlic stalks, leek, onion, and spring onion. The study also found that the association of garlic intake with cancer risk was not significant among those with distal colon cancer. (Xin Wu et al, Asia Pac J Clin Oncol., 2019)
- A meta-analysis of observational studies was carried out by the researchers of Italy to evaluate the associations between allium vegetables intake and the risk of colorectal cancer and colorectal polyps. The study included data from 16 studies with 13,333 cases out of which 7 studies provided information on garlic, 6 on onion, and 4 on total allium vegetables. The study found that a high garlic intake may help in reducing the risk of colorectal cancer. They also found that a high intake of total allium vegetables may be associated with a decrease in the risk of colorectal adenomatous polyps. (Federica Turati et al, Mol Nutr Food Res., 2014)
- Another meta-analysis also found that a high intake of raw and cooked garlic may have a protective effect against stomach and colorectal cancers.(A T Fleischauer et al, Am J Clin Nutr. 2000)
Allium vegetable intake and gastric cancer
- In a study published in 2015, the researchers from Italy evaluated the association between allium vegetable intake and gastric cancer risk in an Italian case-control study including 230 cases and 547 controls. The study found that high allium vegetable consumption including garlic and onion may be associated with a reduced risk of gastric cancer. (Federica Turati et al, Mol Nutr Food Res., 2015)
- A meta-analysis done by the researchers of Sichuan University, China evaluated the association between allium vegetable intake and gastric cancer risk. The analysis obtained data through literature search in MEDLINE for articles published between January 1, 1966, to September 1, 2010. A total of 19 case-control and 2 cohort studies, of 543,220 subjects were included in the analysis. The study found that a high intake of allium vegetables including onion, garlic, leek, Chinese chive, scallion, garlic stalk, and Welsh onion, but not onion leaf, reduced the risk of gastric cancer. (Yong Zhou et al, Gastroenterology., 2011)
Raw Garlic Consumption and Lung Cancer
- In a study published in 2016, the researchers evaluated the association between raw garlic consumption and lung cancer in a case–control study conducted between 2005 and 2007 in Taiyuan, China. For the study, the data was obtained through face-to-face interviews with 399 lung cancer cases and 466 healthy controls. The study found that, in Chinese population, compared to those who did not take raw garlic, ones with high raw garlic intake may be associated with a reduced risk of lung cancer with a dose-response pattern. (Ajay A Myneni et al, Cancer Epidemiol Biomarkers Prev., 2016)
- Another similar study also found a protective association between intake of raw garlic and lung cancer with a dose-response pattern (Zi-Yi Jin et al, Cancer Prev Res (Phila)., 2013)
Garlic and Risk of Esophageal Cancer
In a study published in 2019, the researchers evaluated the association between garlic and the risk of esophageal cancer in a population-based study with 2969 esophageal cancer cases and 8019 healthy controls. Data was obtained from food frequency questionnaires. Their findings suggested that a high intake of raw garlic may help in reducing the esophageal cancer risk and may also interact with tobacco smoking and alcohol consumption.(Zi-Yi Jin et al, Eur J Cancer Prev., 2019)
Different observational studies suggest that consumption of allium vegetables may help in reducing the risk of different types of cancers. However, these protective associations may be specific to the vegetable consumed. Allium vegetables such as garlic may help in reducing the risk of breast cancer, prostate cancer, lung cancer, colorectal cancer (but not distal colon cancer), gastric cancer, esophageal cancer and liver cancer. While onions are good for reducing the risk of gastric cancer and handling hyperglycemia (high blood glucose) and insulin resistance in breast cancer patients, they may not have any significant effect on prostate cancer risk, and cooked onions may even increase the risk of breast cancer.
Hence, always consult your nutritionist or oncologist to ensure that the right foods and supplements are included as part of your diet for cancer care or prevention.
Cancer patients often have to deal with different chemotherapy side effects which affect their quality of life and look out for alternative therapies for cancer.Taking the right nutrition and supplements based on scientific considerations (avoiding guesswork and random selection) is the best natural remedy for cancer and treatment related side-effects.