Overview

Dimocarpus longan, commonly known as longan or dragon’s eye, is a subtropical fruit tree belonging to the soapberry family ‘Sapindaceae’.¹ It is native to Southern and Southeastern Asia with Thailand and China accounting for the majority of fruit production. 

The longan fruit, similar in texture and taste to the Lychee, is renowned across the world for its health benefits. It has a muskier taste profile in comparison to the lychee and can be consumed fresh, dried or canned. The hard outer shell is peeled off before eating the soft translucent flesh inside. A brown seed is found in the middle and is not meant to be eaten.

Well-known within Traditional Chinese medicine for its high antioxidant nutritional profile, and dubbed the ‘king of fruits’, it has been used for thousands of years to treat a variety of diseases and boost different aspects of health. Properties claimed range from anti-ageing, antioxidant and anti-inflammatory to memory-boosting and sleep-enhancing benefits.¹ 

However, this article will just focus on how longan can improve your skin health and the different ways you can incorporate it into your diet.

What are antioxidants?

An antioxidant is defined as any substance that delays, prevents or removes oxidative damage to a target molecule.² 

Many chemical reactions occur in the body to enable it to function, some of these are called oxidative reactions. When an oxidative reaction occurs, molecules called ‘free radicals’ are produced. Oxidative reactions can be a part of normal and a necessary functions, being required for many different reasons, however, the free radicals they produce as a by-product can be harmful. Free radicals create chain reactions within the body that lead to unnecessary inflammation and damage or death of healthy cells. 

Oxidative reactions are common and often important biological processes in the body and we have a natural protective system which quickly neutralises free radicals produced, however, pollution, smoking, poor diet, UV radiation and lack of exercise can all increase the number of unnecessary oxidative reactions and thus overwhelm our bodies natural protective mechanisms and increase the amount of oxidative damage. Damage caused by free radicals has been found to play an important role in the development of many different diseases including heart disease and cancer. Therefore, limiting oxidative damage through the inclusion of antioxidants in our diet is very important.²

Antioxidants quickly remove harmful free radicals or work to prevent unnecessary oxidative reactions from occurring, thereby limiting the number of free radicals that can cause chain reactions that result in inflammation and damage to the body.² 

Why are antioxidants important for skin health?

Oxidative reactions can lead to the development of inflammation and damage or death of healthy cells. These can occur anywhere in the body including within the skin. 

The skin is the largest organ in the body. Its primary function is to act as a barrier against chemical, physical and biological assault.³ It is composed of three layers, the outer layer called the ‘epidermis’ which provides the barrier function and has a very high number of cells, a middle layer called the ‘dermis’ and a bottom layer called the hypodermis. 

The dermis is responsible for the strength and elasticity of the skin, creating new skin cells using fibroblasts and providing nutritional support to the epidermis, it is particularly rich in collagen.⁷ 

The hypodermis connects your dermis to muscle and bone, acts as a shock absorber and contains your fat cells which insulate the body. It also contains sweat cells which help regulate proper body temperature and prevent it from overheating.

To maintain the integrity of your skin, the cells in your skin are constantly dividing and undergoing chemical reactions many of which are oxidative and result in the production of harmful free radicals.³ Your body has processes by which it rapidly sweeps up these free radicals to prevent them from doing damage. 

However if either the balance is out of kilter, or your skin is undergoing an unusually high number of oxidative reactions due to various stressors, then your body will not be able to prevent damage caused by the free radicals fully. This can contribute to the development of a number of skin diseases as well as exacerbating the ageing process.³

The nutritional profile of longan

100g of longan fruit contains:

• Water: 82.8g
• Energy: 60 kcal
• Protein: 1.31g
• Total Carbohydrate: 15.1g
• Fibre: 1.1g 

Vitamins and minerals:

• Vitamin C: 84mg (140% DV)
• Calcium: 1mg
• Iron: 0.13mg
• Magnesium: 10mg
• Potassium: 266mg^4,5

Antioxidant substances in longan

The profile above indicates that longan contains high levels of Vitamin C which is a well-known antioxidant.

In addition, the skin, flesh and seed of the longan fruit have been found to contain an abundance of polyphenols, which also have strong antioxidant properties. The most abundant polyphenols within longan are 4-methyl catechol, chlorogenic acid, vanillic acid and Gallic acid.^11,12,13 

Longan also contains flavonoids, a subclass of polyphenols, which are not only strong antioxidants but also anti-inflammatory and anti-carcinogenic.⁶ The most abundant flavonoids found in longan are Epicatechin and Quercetin.^4,5,14

Benefits of longan for skin health

Vitamin C and skin health

Vitamin C is an essential dietary component because humans are unable to synthesise it themselves, which means that all of our physiological needs for vitamin C must be met by our dietary intake. Much of what we know about the impact vitamin C has on our body has come from the study of scurvy, which is a haemorrhagic disease resulting from vitamin C deficiency.⁸ 

Vitamin C is essential for the development of connective tissue and plays a leading role in bone formation, wound healing and maintaining healthy skin and gums. As already mentioned, it is also a potent antioxidant.⁸

The skin contains high levels of Vitamin C, which has been absorbed from the bloodstream and transported through the dermis into the epidermis.⁷ It has been found that Vitamin C levels are lower in aged and photo-damaged skin, however, whether this is cause or effect is currently unknown.⁷ 

Studies have shown that the beneficial effects of Vitamin C on skin health are due to the important role it plays in collagen formation and its antioxidant properties. 100g of longan fruit contains 140% of your daily nutritional need for Vitamin C. This makes longan an exceptionally good source of dietary Vitamin C and therefore an aid to skin health.

Vitamin C and collagen formation

In the skin, collagen’s main role is to give it structure, strength and elasticity and to help the development of new skin cells which enables it to regenerate and repair.⁷ 

Collagen is produced by fibroblasts found within the dermis. Vitamin C is a key component involved in the formation of collagen. A deficiency of Vitamin C leads to a reduction in collagen synthesis.⁷ Collagen, or a lack thereof, plays a significant role in the ageing process of the skin. A reduction in collagen leads to the loss of skin structure, elasticity and dermal thickness resulting in fine lines and wrinkles.⁹ 

Antioxidant properties of vitamin C

Vitamin C is a well-known potent antioxidant that removes free radicals produced by oxidative reactions, preventing them from damaging and killing cells and causing inflammation. This is of particular importance within the skin as environmental pollutants and exposure to UV radiation can increase the amount of oxidative reactions.⁷ Cell death and chronic inflammation within the skin can cause a number of dermatological conditions as well as being a major contributor to premature ageing. Therefore, sufficient consumption of longan with its high levels of Vitamin C could help prevent skin damage and aid skin health.

Polyphenols and skin health

Polyphenols are a large and important group of natural compounds commonly found in fruits and vegetables.¹⁰ They are well-known for their antioxidant, anti-inflammatory and anti-cancer properties. Flavonoids are the best-known sub-group of polyphenols and are antioxidants. 

Longan contains many polyphenols and flavonoids including the potent antioxidant ‘Quercetin’.⁵ These, like Vitamin C, work to clean up free radicals that have been produced from oxidative reactions before they can cause damage to skin cells.

Skin ageing is a natural phenomenon, however, it is often prematurely accelerated. One of the main factors that has been found for this acceleration is damage caused by free radicals to skin cells.¹⁰ Both UVA and UVB are significant perpetrators of oxidative reactions in the skin.¹⁰ The damage caused to the skin from oxidative stress caused by excessive UV radiation is the predominant cause of the formation of wrinkles and the mutation of skin cells, which can result in skin cancer.¹⁰ 

Increased oxidative stress in the skin also plays an important role in the development of other dermatological diseases such as atopic dermatitis (eczema), psoriasis, lichen planus, acne vulgaris and alopecia.¹⁰

How to incorporate longan into your diet

Longan can be consumed fresh, canned or dried allowing it to be easily included in your diet in different ways. Below are some common ways to prepare and eat longan:

• Eat fresh: peel away the outer shell and eat around the seed in the middle. Save the seed and attempt to grow your own longan tree
• Add to a smoothie: remove the outer shell and the seed and add the flesh to a smoothie along with coconut milk and banana to give it a sweet creamy flavour
• Make a dessert: Due to their natural sweetness, they are a popular addition to a variety of desserts such as ice creams, sorbets and cheesecakes
• Make a jam: use longan to make a sweet jam which can be eaten with biscuits or on bread
• Eat dried: just like with other dried fruits such as apricots or pineapple, these can make a tasty and nutritious snack

Considerations and precautions

Before deciding on whether to start including longan in your diet here are a few factors to take into consideration: 

• High sugar content: people with diabetes or dysglycemia (blood sugar is too low or too high) should be cautious of longan’s high sugar and low fibre content 
• Not recommended during pregnancy: it is thought that longan can increase your body temperature and it is therefore not recommended for consumption during pregnancy
• Pesticide poisoning: many longan farmers, particularly in China, use pesticides to cultivate the production of their fruit, so it is not unheard of for longan to be associated with pesticide poisoning, especially in those who peel the skin off using their teeth. There are however organically grown versions of the fruit available which mitigate this risk¹⁵

Summary

Longans are a sweet fruit similar to lychees that is found in Southern and Southeastern Asia. It has been used by generations of traditional Chinese medicinal practitioners to boost health and to help treat a wide range of diseases. 

It is rich in vitamin C and polyphenols which give it strong antioxidant properties. These help to boost skin health and prevent premature ageing by preventing damage caused by UV radiation and other stressors such as pollution. Vitamin C also plays an important role in the production of collagen which maintains the skin's integrity and prevents the premature formation of wrinkles and fine lines.

The fruit can be eaten fresh, dried or canned although it is not recommended for consumption by pregnant women or those who have blood sugar issues such as diabetes. Additionally, cultivation often involves the use of high levels of pesticides which can lead to pesticide poisoning. 

If you have any concerns, always seek advice from your healthcare professional before consuming Lorgan.