Alliums

Health Benefits of Alliums

The onion family, also known as alliums, includes hundreds of different species belonging to the genus Allium, although the ones we’re most likely to see on a dinner plate are onions, garlic, leeks, chives, scallions, and shallots. The word “allium” is believed to derive from the Greek ἀλέω (or aleo), which means “avoid,” and refers to the potent odor of these vegetables! 

Nutritionally, alliums tend to be excellent sources of fiber, vitamin B6, folate, vitamin C, vitamin K, manganese, potassium, and iron. What’s more, alliums boast a number of important phytonutrients—most notably the organosulfur compounds (such as cepaenes and thiosulfinates) that characterize their taste, but also kaempferol, quercetin, fructans, ferulic acid, caffeic acid, anthocyanins (in red- or purple-colored alliums), beta-carotene (in green alliums like spring onions and chives), flavonols (in yellow-fleshed and brown-skinned onions), chlorophyll (in leeks, chives, and scallions), saponins, and myricetin and apigenin (especially in garlic).

Studies show that for every 100 grams per day of alliums, risk of all-cause mortality decreases by 24%. But, we don’t need to eat that much alliums to benefit: Eating ½ serving per day decreases cardiovascular disease by 21% compared to rarely eating alliums, and one study found that men consuming a mere 10 grams of onions per day were 70% less likely to develop prostate cancer than men consuming under 2 grams of onions daily.

Let’s take a look at the health benefits associated with vegetables from the allium family!

Allium Vegetables Are Cardioprotective

A 2020 systematic review and meta-analysis, covering 81 cohort studies (4 031 896 subjects!), examined the impact of different fruits and vegetables with cardiovascular outcomes and found a 67% lower risk of CVD mortality, a 33% reduced risk of coronary heart disease mortality, and an 11% reduced risk of stroke with highest versus lowest consumption of allium vegetables.  Impressive!

Allium Vegetables Protect Against Cancer

Where allium vegetables really shine is in their chemoprotective capabilities.  Epidemiological studies suggest that allium vegetable intake reduces the risk of several types of cancer.  The protective effect appears to be related to the presence of organosulfur compounds, which include dithiolethiones, diallyl sulfide, and sulforaphane.  Organosulfur compounds exert their effects by modulating important enzymes (the cytochrome P450 family and glutathione S-transferases) that help detoxify carcinogens and prevent DNA adducts from forming.  One specific organosulfur compound, diallyl sulfide, also acts as potent antimicrobial properties and can help fight the stomach ulcer bacteria, H. pylori.

Let’s take a look at some of the epidemiolocal studies evaluating allium vegetables and cancer!

A 2021 systematic review and meta-analysis, covering 97 cohort studies, found a 21% reduced risk of ovarian cancer with consumption of allium vegetables.

A 2016 meta-analysis, covering 21 case-control and 4 cohort studies, found a 21% reduced risk for squamous cell carcinoma of the upper aerodigestive tract, when comparing highest versus lowest consumption of total allium vegetables.  Cancers of the upper aerodigestive tract include cancers of the oral cavity, pharynx, larynx, and esophagus.

A 2015 case control study and meta-analysis evaluated the association between allium vegetable intake and gastric (stomach) cancer.  The meta-analysis included 10 case-control and four cohort studies.  A 22% reduced risk in gastric cancer was observed for highest versus lowest intake of allium vegetables.  Data from an Italian case-control study including 230 cases and 547 controls showed a 30% reduced risk in gastric cancer for frequent use of both garlic and onion.  While a 2011 meta-analysis, covering 19 case-control and 2 cohort studies (543 220 subjects) found 46% reduced risk of gastric cancer in highest versus lowest consumption of allium vegetables.  A dose response meta-analysis based on three case-control studies, indicated that an increment of 20 grams of allium vegetables per day was associated with a statistically significant 9% decreased risk of gastric cancer! Overall, an increase in Allium vegetable consumption of 20 gramps per day (approximately the average weight of 1 garlic bulb) was associated with a statistically significant 9% decreased risk of gastric cancer for case control studies from the dose-response meta-analysis. 

Both in vitro and in vivo studies have shown that allium vegetables have an antibacterial effect against H pylori, which is a key risk factor for gastric cancer.  And, a 2016 systematic review showed that in patients infected with Helicobacter pylori (H. pylori), which is the main risk factor for developing gastric cancer, high consumption of allium family vegetables had a protective effect.

A 2014 meta-analysis, covering 16 studies and 13 333 cases, evaluated the association between allium vegetable intake and colorectal cancer and adenomatous polyps (precursors of colorectal cancer).  Based on four studies, a 22% reduced risk of colorectal cancer and a 12% reduced risk of colorectal adenomatous polyps was observed for highest versus lowest intake of total allium vegetables.  

A 2013 meta-analysis, covering six case-control and three prospective cohort studies (including 132 192 subjects), found an 18% reduced risk of prostate cancer for intake of allium vegetables when comparing highest versus lowest consumption.  While a 2002 population-based, case-control study conducted in Shanghai, China found that men consuming 10 grams or more total allium vegetables per day were 49% less likely to develop prostate cancer than men consuming under 2.2 grams daily. 

A 2005 case-control study in Shanghai (832 cases and 846 controls) found a 24% reduced risk of endometrial cancer in the highest versus lowest quartile of allium vegetable intake.  In premenopausal women, the results were even more pronounced with a 59% reduced risk!

To summarize, a variety of prospective cohort and case-control studies have found that overall allium vegetable consumption is associated with lower risk of:

• colorectal cancer (up to an 22% lower risk),
• endometrial cancer (up to a 24% lower risk; 59% lower risk in premenopausal women),
• gastric cancer (up to a 46% lower risk),
• ovarian cancer (up to an 21% lower risk),
• prostate cancer (up to a 49% lower risk), and
• upper aerodigestive tract [including oral cavity, pharynx, larynx, & esophagus] (up to a 21% lower risk).

Yes, allium vegetables are absolute rock stars when it comes to our health!

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