The protective role of onion against neurodegeneration and Alzheimer’s disease can be attributed to active ingredients such as flavonoids, and quercetin in particular. Quercetin is a phytochemical that possesses antioxidant properties and has a protective effect against ageing – it has anti-oxidative, anti-inflammatory, anti-proliferative, anti-carcinogenic, anti-diabetic and anti-viral properties.
Increased oxidative damage is a major factor responsible for the occurrence of age-related neurodegenerative disorders, including Alzheimer’s disease (AD). As with many health-related conditions, oxidative damage increases with age.
The flavonoid compounds in onion root extract, especially quercetin, could provide a protective effect against neurodegeneration and mitigate the effects of AD by improving antioxidant capacity and regulating gene expression patterns.
There is increased interest in using natural products – such as plant polyphenols – against AD because of their high antioxidant capacity, minimal side effects and relative safety. This study aimed to investigate the protective effect of onion and garlic root extracts on brain damage due to AD in rats.
Brain cell apoptosis is one of the primary hallmarks of AD and affects memory function in the hippocampus. Several studies have shown that onion flavonoid intake, specifically quercetin, protects brain tissues against ageing by inhibiting apoptosis which causes brain degeneration.
Quercetin extracted from onion is linked to the prevention of intracellular ROS (reactive oxygen species) generation in the brain tissues of rats with AD. ROS induces oxidative stress by causing damage to the basic building blocks of brain cells including DNA, protein and lipids. It seems quercetin is a potent scavenger for ROS and hence protects the body against oxidative stress.
The study found that supplementation of the AD rats with onion root extracts mitigated symptoms such as brain lesions, alterations in the expression levels of the apoptotic genes, DNA damage and intracellular ROS generation in brain tissues.
The protective role of onion root extract against AD might result from its content of flavonoid compounds such as quercetin that improve the antioxidant capacity and regulation of gene expression patterns.
Practice tips
- Quercetin is commonly found in plant foods, and onion is one of the top quercetin-containing foods in the Australian diet. Half an onion (75g) contains on average 30mg of quercetin
- Quercetin is metabolised in 24 hours, so it’s necessary to consume quercetin daily to maintain the body’s antioxidant capacity. Be sure to include onions in everyday meals to get a daily dose of quercetin
- Sunlight boosts quercetin in the outer layers, so don’t over peel onions
- Don’t throw out onion skins as these contain high levels of quercetin. Simply dry out in the oven and add crushed onion skins to butter or use as a garnish in soups and meals. Onion skins can also be added to a pot of home-made stock – a great way to minimise food waste
Reference
Hegazy EM, Sabry A, Khalil WKB. Neuroprotective effects of onion and garlic root extracts against Alzheimer’s disease in rats: antimicrobial, histopathological, and molecular studies. BioTechnologia (Pozn). 2022 Jun 29;103(2):153-167. doi: 10.5114/bta.2022.116210. PMID: 36606073; PMCID: PMC9642951.
