Slice into the yellow-brown skin of this small fruit and you’ll find milky-white, almost translucent flesh, and a shiny black pit. Because of its appearance, the Chinese call this fruit Dragon's Eye, but it's better known as longan fruit.
While the medicinal value of longan is little-known outside Asia, in China this fruit has been praised for thousands of years for its ability to treat or prevent a variety of health problems, including cancer. Let’s take a closer look at whether longan fruit as a cancer treatment is fact or folklore.
Used in Traditional Chinese Medicine
The Longan tree is native to China and India but is now grown throughout Southeast Asia.
It belongs to the soapberry family, which contains more than a thousand species. The best known is the lychee, which is similar in size and appearance, and for this reason longan is also called 'Lychee's Little Brother'.
Longan has a long history of use in Traditional Chinese Medicine (TCM). Different parts of the plant are used to treat urinary diseases, relieve pain, soothe nerves, aid digestion, reduce fever, expel parasitic worms, and as an antidote to poison. In addition, longan is used to treat bleeding, hernia, swollen lymph glands, insomnia, scabies and eczema.
Early Chinese healer Li Shizhen, who compiled a highly influential materia medica (guide to medicinal substances) in the 16th century, called longan “the king of fruits.”
Contains powerful plant compounds
Nutritionally longan fruit has a very high content of vitamin C. Just 3.5 ounces of longan provides 84 mg of vitamin C. In addition to its immune-boosting, tissue-healing stores of this well-known cancer-fighting vitamin, longan contains high levels of phytochemicals. The root, seed, flowers, leaves, and pericarp (coating of the seed) are rich in cancer-fighting polyphenols. These plant compounds are shown in research to help reduce inflammation, improve brain health, decrease risk factors for heart disease, support insulin sensitivity and help you maintain a healthy weight.
Let’s take a look at some of the most powerful polyphenols packed into the longan tree:
Proanthocyanidins: boast strong antioxidant power, protect against cardiovascular disease, display anti-cancer activity and ease allergies.
Epicatechin: a strong antioxidant shown to benefit heart health and protect against diabetes and cancer. This well-known polyphenol is also found in green tea.
Gallic acid: has antioxidant, anti-inflammatory, anti-fungal and anti-viral properties; acts against cancer cells and may help treat diabetes.
Ellagic acid: an antioxidant, anti-mutagen and anti-cancer agent also found in many berries.
Corilagin: exhibits antioxidant, anti-tumor, anti-inflammatory, liver-protective and blood-pressure-lowering activity.
Quercetin: antioxidant, anti-inflammatory, anti-tumor activity. Lowers blood sugar and may help prevent heart disease. Also found in apples, onions and other foods.
Kaempferol: shows promise in being an anti-obesity and anti-cancer agent. Found in other sources ranging from apples and oranges to tea and wine.
Longan in cancer research
As you can see, longan contains a number of plant phytochemicals that have anti-cancer properties. The flower extract has epicatechin and proanthocyanins as major components, while the seed extracts contain gallic acid, corilagin and ellagic acid.
Extracts of the flowers and seeds have been tested on a number of different cell lines and found to act against cancers of the colorectum, liver, lung, cervix and breast.
When researchers tested the flower extract in two human colorectal cancer cell lines, it inhibited their growth. The higher the dose, and the longer the flower extract was applied, the greater the effect.
The scientists wrote, "The results strongly indicate that LFE [longan flower extract] is capable of influencing the malignant potential of CRC [colorectal cancer] cells."
They put the mechanisms down to cell-cycle arrest through the hampering of DNA synthesis, and also by apoptosis (cancer cell "suicide") through the suppression of the anti-apoptotic protein Bcl-2.
The seed extract was found to act in a similar way to the flower extract on colorectal cancer cells. The seed extract was also effective in the other cancers listed, in particular, a highly aggressive and invasive breast cancer cell line whose viability decreased to less than 60 percent of the viability of untreated cells.
The researchers concluded that "recent advanced studies have validated the novel pharmaceutical functions of [these extracts], especially their anti-cancer functions."
A pericarp, or seed coating, extract of longan was also found to inhibit liver, lung and stomach cancer cells.
For cancer to spread it needs to dissolve surrounding connective tissues. Matrix metalloproteinases (MMPs) are enzymes that allow it to do just that. Dried longan seeds were found to prevent this process.
"Notably, dried longan seeds have been established not only as major sources of antioxidants, but also as potent MMPs inhibitors,” wrote the scientists from Taiwan. “Since these properties are associated with anti-cancer effects, dried longan seeds could be a novel natural source for compounds used in chemoprevention and chemotherapy."
Valuable for almost every condition
The key benefits of longan were outlined by scientists at the Chinese Academy of Agricultural Sciences and published in the Journal of Medicinal Plant Studies last year.
"All in all, the most important health benefits of longan are skin care, anti-aging, boosts libido, anti-anxiety, treats insomnia, blood tonic, promotes weight loss, increases energy, controls blood pressure, neuroprotection, strengthens immunity, speeds-up healing, prevents chronic diseases, aids in digestion, improves memory, vision health, useful in treating snake bites, and appropriate in dental care,” wrote the scientists.
"The obtained findings," they continued, "suggest potential of longan as superfruit."
I think their claims are a bit over the top, given what we know at this point. But the fruit clearly contains many nutrients that we know are valuable from other research.
Another group of Chinese scientists wrote -- in relation to the flowers and seeds only -- that "their multiple medical functions...and especially the reduction of swelling as recorded in the TCM pharmacopoeia, imply that these two TCMs [flowers and seeds] can be applied in cases of microbial infection, inflammation, and metabolic diseases. Evidence to this end has been revealed by current scientific methods during the past decade."
Human evidence is lacking
Unfortunately, there are zero human studies on longan, which means all the benefits listed by Chinese scientists are based on studies in a petri dish, a small number of animal studies, as well as centuries of traditional use.
One of longan’s traditional uses is as a sleep aid and to reduce anxiety. Japanese scientists found an extract of longan contained appreciable amounts of adenosine, a brain chemical that depresses the central nervous system and promotes sleep.
Another traditional use is pain relief. An entire paper was devoted to the antioxidant and anti-inflammatory properties of the fruit. It was published in Evidence Based Complementary and Alternative Medicine in 2012.
The scientists found longan extract suppressed inflammation-promoting nitric oxide and TNF-α, and blocked COX 2, the key inflammatory enzyme which is also the target of pain-killing drugs like Celebrex. This laboratory research is very promising, and longan’s long history of use in Traditional Chinese Medicine certainly counts for something.
Where to buy longan
Longan is a tropical, sweet, juicy and succulent fruit that ripens in the summer. It's not sold fresh in many places, but you might find it in some stores in California, Florida, and the southernmost states in between. It's more likely to be discovered in Asian markets.
Dried, tinned, packaged longan is more readily available.
If you have a green thumb, in some nurseries you can buy a longan sapling or propagate one from a seed. You can grow longan in a container where it reaches seven feet tall, or outside where it can grow to 40 feet in both height and width. In a good year the tree may produce 500 pounds of fruit. That’s a lot of antioxidant power!
Best regards,
Lee Euler,
Publisher
References:
- Modern pharmacological actions of Longan fruits and their usages in traditional herbal remedies
- Potential roles of longan flower and seed extracts for anti-cancer
- Adenosine, the anxiolytic-like principle of the Arillus of Euphoria longana
- Antioxidant and Anti-Inflammatory Properties of Longan Pericarp
- https://www.semanticscholar.org/paper/Antioxidant-and-anti-matrix-metalloproteinases-of-Panyathep-Chewonarin/93d42c0c371c9c77f0b35b86f3834094f0defd0a
