Longan is a fruit that has traditionally been used for its neuroprotective and cognitive-boosting ability.
It’s found in some nootropics.
Research on the medicinal purposes of this fruit, its seeds and its extracts is limited. Further studies are needed to determine its efficacy. Early results, however, are promising.
Longan is also known as Dragon Eye or Euphoria. Longan seeds are found to contain high levels of some beneficial polyphenolic compounds such as corilagin, gallic acid and ellagic acid (1).
Longan has memory-enhancing effects. Dried longan fruit has long been prescribed as a tonic and for the treatment of forgetfulness and insomnia in traditional Chinese medicine. To assess its efficacy in a clinical setting, researchers evaluated the effects of aqueous extract of the fruit on learning and memory in a 2010 study.
The extract was administered to mice for 14 days. Memory was assessed using the passive avoidance task. Results reveal that the step-through latency in the longan-treated group was significantly increased compared to the vehicle-treated group in the passive avoidance test (a step-through latency is defined as learning).
In addition, it was noted that treatment significantly enhanced immature neuronal survival, but not neuronal cell proliferation.
Researchers believe that its beneficial effects are mediated by brain-derived neurotrophic factor (BDNF) — a family of proteins that plays an important role in neuronal survival and growth and serves as a neurotransmitter modulator which is essential for learning and memory (2,3).
Longan may have anti-fatigue effects. Preliminary tests show the potential of longan seed polysaccharides as an anti-fatigue agent. Using a mouse model, researchers administered longan seed polysaccharides to mice at doses of 50, 100, 200 and 400 mg/kg.
Anti-fatigue activity was evaluated using a swimming test, along with the determination of serum urea nitrogen, hepatic glycogen and blood lactic acid content.
The results show that longan seed polysaccharides, in doses ranging from 50 to 100 mg/kg, extended swimming time, increased hepatic glycogen, reduced blood urea nitrogen and decreased blood lactic acid in the mice (4).
Longan has neuroprotective properties. A 2012 study was performed to evaluate the neuroprotective effect of longan flower water extract in rats with induced neurotoxicty. The antioxidative activity of the extract proved to be more potent than glutathione or Trolox (a water-soluble derivative of vitamin E with powerful antioxidant properties). Furthermore, there was indication that the brains of longan extract-treated rats were more resistant to oxidative stress.
Another promising result of the study revealed that oral administration of the water extract (125-500 mg/kg/day) in a Parkinsonian animal model attenuated 1-methyl-4-phenylpyridinium (MPP(+))-induced neurotoxicity in the nigrostriatal dopaminergic system of rat brain (In Parkinson’s disease, loss of dopaminergic nigrostriatal neurons is what is thought to cause the motor symptoms characteristic of the disease) 5.
Longan has the ability to alleviate injury from cerebral ischemia in rats. Researchers of a 2011 study concluded that polysaccharides of longan are capable of alleviating injury by a mechanism that may involve decreasing oxidative stress.
Among other things, the polysaccharides reduced the neurological function score, brain water content and the infarct volume — one of the common indexes for assessing the extent of ischemic brain injury following cerebral ischemia (6,7).
Longan may be an immunotherapeutic adjuvant. Oral administration of longan pulp polysaccharide-protein complex showed strong immunomodulatory activity in immunosuppressed mice.
Compared with the model control, administration of 100 mg/kg could significantly enhance antibody production, and the beneficial effects of 50-200 mg/kg were comparable to those of 50 mg/kg ganoderan — a bioactive from Ganoderma Lucidum, a potent immune system regulator (8).
Longan may have anti-obesity and hypolipidemic effects. Anti-obesity and hypolipidemic (lipid lowering) effects of polyphenol-rich longan flower water extract were investigated in a rat model study.
Eight male rats per group were assigned randomly to one of the following dietary groups: normal-caloric diet and pure water; hypercaloric diet and pure water; hypercaloric diet and 1.25 percent longan flower water extract; and hypercaloric diet and 2.5 percent longan flower water extract for nine weeks.
Results revealed body weight, size of epididymal fat, serum triglyceride level and atherogenic index, and hepatic lipids were decreased in the hypercaloric diet and 2.5 percent longan flower water extract group (9).
Longan has free-radical scavenging ability. The goal of a 2007 study published in Food and Chemical Toxicology was to examine the free radical scavenging activity of longan seed extract by using three different assay methods.
Dried longan seed extracts exhibited the highest radical scavenging activities when compared to fresh seed and dried pulp extracts.
For scavenging activity of DPPH and superoxide radicals, longan seed extract was found to be as effective as Japanese green tea extract while dried longan pulp and mulberry green tea extracts showed the least scavenging activities.
Preliminary observations suggest that longan seed extract could be a potential source of potent natural dietary antioxidants (10).
Longan has anti-inflammatory properties. As part of a 2012 study, published in Evidence-Based Complementary and Alternative Medicine, researchers noted that administration of longan water extract in the range of 100-400 mg/kg, showed an inhibition on paw edema development following carrageenan treatment in mice.
It is believed anti-inflammatory effects of the water extract may be related to nitric oxide and tumor necrosis factor (TNF-α) suppression and associated with the increase in the activities of antioxidant enzymes, such as catalase, superoxide dismutase and glutathione peroxidase (11).
A 2012 study evaluating the acute and repeated dose (4 and 13 weeks) of aqueous extract of longan seed in animals revealed no significant toxicological effects.
In addition, growth pattern (body weights, food consumption and relative organ weights), hematology analysis, and clinical biochemistry analysis in all treated animals were in normal physiological ranges (12).
Researchers stress the need for clinical trials in humans to determine whether there are any adverse reactions.
There have been reports of gastrointestinal issues ranging from nausea and vomiting to cramping and constipation when eating the fruit.
Due to a lack of clinical trials done in humans, there is no recommended dosage.
Longan is a fruit that has traditionally been used in Traditional Chinese Medicine for its neuroprotective and cognitive-boosting ability. Studies on this fruit are limited, but preliminary results show its promise in its memory-enhancing effects, anti-obesity and hypolipidemic effects, anti-fatigue effects, anti-inflammatory effects and its immunotherapeutic and neuroprotective properties.
It is believed that high levels of beneficial polyphenolic compounds such as corilagin, gallic acid and ellagic acid found in longan seeds are what give it its therapeutic benefits.