Though all vegetables are important for health, certain kinds offer unique benefits.
Onions are members of the Allium genus of flowering plants that also includes garlic, shallots, leeks and chives.
These vegetables contain various vitamins, minerals and potent plant compounds that have been shown to promote health in many ways.
In fact, the medicinal properties of onions have been recognized since ancient times, when they were used to treat ailments like headaches, heart disease and mouth sores (1Trusted Source).

1.Sleep and mood

Folate, found in onions, might help reduce depression. Homocysteine prevents blood and other nutrients from reaching the brain, and folate prevents this chemical from building up. Excess homocysteine also interferes with the production of the feel-good hormones serotonin, dopamine, and norepinephrine, which regulate not only mood, but also sleep and appetite.

Onions are nutrient-dense, meaning they’re low in calories but high in vitamins and minerals.
One medium onion has just 44 calories but delivers a considerable dose of vitamins, minerals and fiber (2Trusted Source).
This vegetable is particularly high in vitamin C, a nutrient involved in regulating immune health, collagen production, tissue repair and iron absorption.
Vitamin C also acts as a powerful antioxidant in your body, protecting your cells against damage caused by unstable molecules called free radicals (3Trusted Source).
Onions are also rich in B vitamins, including folate (B9) and pyridoxine (B6) — which play key roles in metabolism, red blood cell production and nerve function (4Trusted Source).
Lastly, they’re a good source of potassium, a mineral in which many people are lacking.
In fact, the average potassium intake of Americans is just over half the recommended daily value (DV) of 4,700 mg (5Trusted Source).
Normal cellular function, fluid balance, nerve transmission, kidney function and muscle contraction all require potassium (6Trusted Source).
3.Digestion
The fiber in onions promotes good digestion and helps keep you regular. Additionally, onions contain a special type of soluble fiber called oligofructose, which promotes good bacteria growth in your intestines. One 2005 study in Clinical Gastroenterology and Hepatology found that oligofructose may help prevent and treat types of diarrhea. The phytochemicals in onions that scavenge free radicals may also reduce your risk of developing gastric ulcers, according to the National Onion Association.

4.Promote Hair Growth

The number one reason onion juice is good for hair growth is it contains sulfur, which is also found in amino acids. And keratin (an important protein) is also sulfur-rich and is required for strong hair. When applied to the scalp, onion juice provides this extra sulfur for stronger and thicker hair. This sulfur can also stimulate collagen production – which, in turn, aids in the production of healthy skin cells, and, hair growth (by default, treating hair thinning too).
Applying onion juice to hair and scalp can increase blood supply to the hair follicles, enhancing hair growth. It can also give you voluminous hair. In one study, participants who washed their hair with onion juice had experienced more hair growth than those who hadn’t (42). However, more research is required. But then, using onion juice on your hair is not harmful.
You can simply massage fresh onion juice into your scalp and hair. Leave it on for 15 minutes, post which you can wash as usual using a shampoo.