Dimocarpus longan, commonly known as the longan (langan/), is a tropical tree species that produces edible fruits. It is one of the better-known tropical members of the soapberry family Sapindaceae, to which the lychee and rambutan Also belong.
The fruit of the longan is similar to that of the lychee, but less aromatic in taste. It is native to tropical Asia and China.
The longan (from Cantonese luhng-ngaahn, literally dragon eye), is so named because it resembles an eyeballs when its fruit is shelled (the black seed shows through the translucent flesh like a pupil/iris). The seeds is small, round and hard, and of an enamel-like, lacquered black.
The fully ripened, freshly harvested fruit has a bark-like shell, thin, and firm, making the fruit easy to peel by squeezing the pulp out as if one were “cracking” a sunflower seed.
When the shell has more moisture content and is more tender, the fruit becomes less convenient to shell. The tenderness of the shell varies due to either premature harvest, variety, weather conditions, or transport/storage conditions.
Longan fruit has been used in Traditional Chinese Medicine for thousands of years as remedy for many diseases, ranging from insomnia to snakes bites.
Researchers suspect that active compounds and antioxidants in longan may support cognition, brain and heart health, and immune defense – but how strong is the existing evidence?
The longan fruit is used as in Traditional Chinese Medicine Medicine (TCM) as a sleep aid, relaxant, to improve digestion, alleviate nerve pain, reduce fever, clean parasites, and even as an antidote to snakes poison.
The fruit looks like an eyeballs when peeled, which earned it the name “dragon’s eye” in Chinese.
The fruit, flowers, and seeds of longan are all used to prepare traditional remedies. Longan flowers are sold in herb markets, have a fruity aroma, and are used to prepare an infusion in Taiwan.
The powder of dried longan seeds is traditionally used to reduce bleeding, relieve swollen lymph glands, and soothe eczema.
Longan fruit is succulent and has gained popularity as an exotic refreshment. Longan fruit is now produced in large quantities in China. Wine from the longan fruit is also considered a “functional food” in TCM, used for various ailments.
ACTIVE COMPOUNDS & MECHANISMS
Longan flowers, seed, pulp, and the whole fruit contain a unique combination of bioactive compounds, many of which are still poorly understood.
Longan flowers and seeds are rich in polyphenols, which are antioxidants. They contain proanthocyanidins, which are also the main active compounds in grape seed extract and have been researched for supporting heart and immune health.
LONGAN FRUIT, PULP, AND EXTRACT CONTAIN:
● Antioxidants, such as allergic acid, quercetin, and kaempferol.
● Polysaccharides, which may boost immunity.
● Adenosine,which is implicated in sleep and relaxation. Adenosine is also produced naturally in the body and is suspected to boost restorative deep sleep (opposite to caffeine).
● Uridine, which seems to boost cognition and mood in animals.
● Chlorogenic acid, which might support weight loss and protect the heart
● GABA, the main “calming” and “relaxing” neurotransmitter.
● Vitamin C
● Corilagin, which is being researched for reducing blood pressure.
Longan leaf extract, although even less researched and used, seems to be rich in unusual and potentially anti-inflammatory sigar-bound flavonoids. Two of these compounds were completely unknown to science until recently – and they have yet to be studied in humans.
POTENTIAL HEALTH BENEFITS OF LONGAN
In a study of 200 pregnant women with anemia, a Traditional Chinese Medicine (TCM) combination, which included longan increased red blood cells count and hemoglobin. As an add-on remedy, it had a stronger effect than just the standard treatment (ferrous fumarate, vitamin C, and folic acid) after 2 weeks.
The same combination used for 2 weeks could also boost red blood cell, hemoglobin, and improve anemia in older people and in women with anemia.
In all three of the above studies, longan was used as part of “dietotherapy,” a TCM approach that involved 6 g dried pulp and 2 eggs per day along with other specific herbs. The exact contribution of longan to the observed effects is unknown.
Dried seeds of longan fruit have long been used as a traditional remedy for insomnia. The indication in TCM for longan is to “revitalize the heart & spleen, nourish blood & calm the mind.”
Animal studies point to sleep-enhanching effects: longan improved sleep in stressed mice.
In mice, longan seed did not directly improve sleep but enhanced the effects of a sleep-inducing sedative (pentobarbital) by boosting GABA activity in the brain. We can’t translate findings from lab animals to humans.
Longan also contains adenosine, which had anxiety-relieving effects in mice. Adenosine is sometimes viewed as the body’s natural sleep aid, and one that caffeine blocks.
Scientists hypothesize that the adenosine content in longan may help explain its traditional use for sleep and anxiety, but proper clinical trials are required to verify this.
Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefits.
■ BRAIN HEALTH
Longan flowers appeared to prevent Parkinson’s disease in rats. The authors suspect longan protected dopamine neurons in the brain from damage. Scientists are also investigating whether longan can boost antioxidants and reduce inflammation in brain cells.
In another animal experiment, polysaccharides from longan reduced brain damage in rats with stroke and increased antioxidants enzymes such as glutathione and SOD in the brain. They also increased the activity to gene’s that are hypothesized to protect brain cells.
A Traditional Chinese Medicine herbal mix containing longan seemed to prevent brain damage in mice with Alzheimer’s disease. This herbal mix was thought to activate an antioxidant protein (Ho-1) in the brain’s memory hub, the hippocampus.
Scientists investigated how longan pulp increases the activity of white blood cells in cell studies.
The polysaccharides in longan are hypothesized to be its strongest immune-boosting compounds, but this hasn’t been confirmed. Researchers only suspect that the immune-enhancing effects might be stronger in a less acidic environment-at least in test tubes.
In one cell study, scientists explored whether longan polysaccharides increased in the number of spleen immune cells (splenocytes), whether these immune cells can ingest and degrade harmful foreign materials, and if longan can activate natural killer cells.
In one experiment, longan pulp polysaccharides increased antibody production in mice with suppressed immune systems.
Different polysaccharides in longan were also studying for enhancing the activity of immune B-cells, which make antibodies and are part of the Th2 response.
■ ANTIOXIDANTS ACTION
Longan is rich in gallic acid and ellagic acid, which have been described as excellent antioxidants. Researchers are studying if the fruit’s extract can neutralise free radicals and reduce inflammation in immune cells. The effects of longan extract and its antioxidants haven’t been investigated in humans, though.
In mice, longan extract appeared to reduce inflammation by boosting antioxidant enzymes such as glutathione and SOD.
Longan seeds extracts contain more ellagic acid than mango kernel extract.
Scientists hypothesize that the antioxidants in longan may affect antioxidant enzymes and inflammatory pathways, but human data are lacking.
In immune cells, researchers explored whether longan reduces citric oxide and TNF-alpha, both of which propel inflammation. Its effect on blocking a key inflammatory enzyme, COX-2, was also investigated. A group of common OTC painkillers ((NSAIDs) work by blocking COX-2.
In another cell study, the flower extract was studied for reducing nitric oxide and inflammation better than the seed and pulp. The authors proposed that it might block inflammatory pathways that increase cytokines on a DNA level (NF-kB and AP-1, MAPK), but far more research is needed.
The impact of longan on diabetes in humans is unknown.
Longan flower extract improved insulin resistance in mice fed a high-sugar diet. It also appeared to boost antioxidant defense and prevent high blood pressure.
Scientists think it merits to be researched in clinical trials of people with metabolic syndrome, a condition marked by insulin resistance.
■ HEART HEALTH & BLOOD PRESSURE
A component from longan seeds (corilagin) reduced blood pressure in rats with high blood pressure.
The authors hypothesize that longan may act by relaxing the blood vessels, reducing the fight-or-fligh response, and decreasing noradrenaline. Clinical trials are needed to verify these proposed mechanisms.
In test tubes, longan leaves could somewhat block the enzyme (XOD) that causes uric acid buildup in gout. Many drugs used to treat gout black this enzyme, but their effectiveness has been clinically verified.
In the same cellular study, longan leaves had a weaker effect compared to the typical gout medication (allopurinol), while the fruit didn’t affect the XOD enzyme at all. The effects o longan were much weaker compared to papaya, which out did even the contraventional medication in this specific test (that doesn’t mean papaya is more effective than gout medication, though.
Scientists are also exploring whether longan seeds can block this pathway in cells. The seeds also seem to reduce blood uric acid levels in mice with gout.
In mice, the extract increased BDNF in the hippocampus, considered to be the most important brain region for memory one of the few ones where we know new brain cells can be created. This extract could also increase the survival of young brain cells.
A mix of 4 herbs including longan improved memory in mice with Alzheimer’s disease. It could also protect the brain from oxidative stress, which might be important for preventing cognitive decline.
■ FAT BURNING
Although a couple of animal studies have been carried out, we know nothing about the impact of longan on fat burning and weight loss in humans. Have in mind that weight loss in lab animals – under controlled and unnatural settings – often doesn’t translate to any meaningful effects in humans.
That said, longan fruit extract prevented weight gain and a rise in blood lipids in rats fed a high-calorie diet. Its proposed effects wide included all of the following:
● Reduced body weight and overall fat
● Reduced blood triglycerides levels
● Reduced liver fats
● Reduced the activity of Gene’s implicated in storing fats in the body (FAS)
● Increased the activity of Gene’s that reduce LDL (LDLR)
● Increased PPAR alpha, which is hypothesized to boost metabolism and fat burning
● Enhanced fat elimination through the stool
Longan fruit extracts also contain probiotics bacteria (Pediococcus pentosaceus), a type of lactic acid bacteria. This plant-based probiotic reduced weight gain, overall and liver fats in obese mice fed a high-fat diet. As with longan extract, human data on this probiotic strain are lacking.
According to one unverified theory, Logan’s antioxidant compounds (which might neutralize free radicals) and its glucose-reducing and insulin-sensitizing potential warrant further research in the anti-aging science domain.
Researchers explored whether longan could reduce glycation in cells, a process that theorized to contribute to aging. Glycation is a process during which important proteins and DNA are changed and their activity altered. Limited research suggests that people with diabetes, due to high blood sugar, might be especially affected by it.
Proanthocyanidins in longan fruit seemed to increase the response to insulin in animals. Theoretically, this might help prevent complications and gang-related health problems in people in diabetes.
■ ENERGY LEVELS
Some scientists believe that the polysaccharides in the seed extract may reduce fatigue and boost energy. In mice, they enhanced endurance, increased energy stores, and reduced lactic acid, which causes muscle fatigue and cramps. Clinical studies haven’t been conducted.
■ BONE HEALTH
One study explored whether longan fruit extract increases the activity of home-building cells.
■ CANCER RESEARCH
Longan contains compounds that were researched mostly in cancer cells. A couple of experiments were done on lab animals. Scientists believe that phenolic compounds, flavonoid, and polysaccharides found in the flower, fruit, or seed may have some value, but this is still uncertain.
Remember that many substances have anti-cancer effects in cells. Including downright toxic chemicals like bleach. This doesn’t mean that they have any medical value. On the contrary, most substances (natural or synthetic) that are researched in cancer cells fail to pass further animal studies or clinical trials due a lack of safety or efficacy.
Longan seed extracts were researched in lymphoma, colon, liver, breast, uterine, and lung cancer cells. Based on these experiments, some researchers think that longan deserves to be studied further in breast cancer cells.
On a DNA level, longan is being investigated for affecting the activity genes that help cancer cells devide and spread. Scientists want to know if it can silence cancer-causing genes, also known as “oncogenes,” and turn on cancer-fighting genes, “antioncogenes” in cells.
One of the “bad” genes that is hypothesized to be especially important (cycling D1) is implicated in several aspects of cancer, from its initial growth and spreading to drug resistance and metastasis. The clinical relevance of this gene is still uncertain, though.
Scientists also explored the following types of longan formulations and the pathways they might act upon in cells:
● Longan seed extract on matrix metalloproteinases (in test tubes and in colon cancer cells). MMPs are hypothesized to help cancers invade tissues and cause metastases.
● Longan flower extract on autodestructive mechanisms –caspases and processes in the mitochondria (by increasing Bcl-2) – implicated in cancer and autoimmune and brain diseases.
High-quality longan fruit extracts over their isolated ingredients on liver, lung, and stomach cancers.
One research team is chemically modifying a compound from longan fruit (an alpha D-glucan) to see if it is active against a type of head and neck cancer in cells.
LIMITATIONS AND CAVEATS
Clinical studies investigating the effects of longan are lacking the majority of studies have been done in mice or cells. Just a couple of studies examined the effects of longan as a herbal combination in Traditional Chinese Medicine.
Various studies focused on different parts of the plant, such as the fruit, seed, or specific extracts. The fruit varieties, its parts, and extracts differ a lot in the number of active compounds they contain.
LONGAN SIDE EFFECTS & SAFETY
Keep in mind that the safety profile of longan is relatively unknown, given the lack of well-designed clinical studies. The side effects described here are not exhaustive and you consult your doctor about other potential side effects, based on your health condition and possible drug or supplement interactions.
Some people may be allergic to longan. In one reported case, a man with mango allergies and asthma experienced itching, hives, and swelling after consuming longan.