What is Horse Chestnut?
Horse chestnut trees (Aesculus hippocastanum) are recognized by their large, towering trunks and full branches that tout clusters of white flowers with chestnut-like seeds (also known as conkers or buckeyes). The raw seeds, barks, leaves, and flowers should not be ingested as they contain a poison called esculetin that may lead to increased risk of bleeding and DNA damage [1, 2].
Seeds from horse chestnut trees were traditionally used to reduce joint pain, soft tissue swelling, and fever as well as combat gut and bladder issues. Today, the properly processed horse chestnut seed extract holds promise for treating leg vein problems (chronic venous insufficiency), hemorrhoids, and swelling (edema) .
Other less common health benefits of horse chestnuts are to increase male fertility, relieve eczema, reduce menstrual pain, and heal skin sores .
Components of Horse Chestnut
Escin shouldn’t be confused with esculetin – the poisonous ingredient in non-processed horse chestnuts .
Mechanism of Action
Escin in horse chestnut seeds acts by:
- Reducing swelling by strengthening and narrowing blood vessels (via calcium channels) 
- Strengthening blood vessels (increasing prostaglandin F2)
- Reducing blood clotting and blood pressure (by reducing platelet aggregation) 
- Reducing inflammation (by blocking Nitric Oxide)
- Reducing allergies (by suppressing white blood cells) 
- Fighting cancer by causing cancer cell death (apoptosis) and increasing autophagy 
- Fighting cancer by decreasing cancer cell growth and spreading 
Health Benefits of Horse Chestnut
1) Horse Chestnut Treats Chronic Vein Problems
Leg vein problems can result in chronic venous insufficiency (CVI). Valves in veins help carry blood from the legs back to the heart. When the valves become weakened or damaged, you may experience swelling, pain, fatigue, tension, and itching in the legs.
Numerous human studies confirm the benefits of horse chestnuts for treating chronic vein problems. Horse chestnut seeds reduced the number of fluids in lower legs as well as ankle and calf swelling in people with chronic leg problems (Systematic Review of 17 studies) .
Compared to placebos, horse chestnut reduced leg swelling, pain, fatigue, and itching based on 21 clinical trials (DB-RCT) involving ~12,000 CVI patients (2-12 weeks, oral dosages 100-150 mg daily) .
2) Horse Chestnut Reduces Swelling
Edema is caused by the buildup of fluids under the skin, leading to swelling. It can affect the lower legs and feet, and symptoms include stiff joints, aching limbs, skin color changes, and weight gain .
In two clinical trials, 125 patients who received escin injections (5-10 mg twice a day) after surgery noticed reduced temperature and swelling 3-4 days after surgery .
Escin also increased the contraction of veins, helping to push blood back to the heart and decrease swelling (via reducing calcium sensitivity) in rat muscle cells .
3) Horse Chestnut Strengthens Small Blood Vessels
Escin may strengthen small blood vessels (capillaries) that otherwise become swollen when weakened.
In a tissue study on human leg veins, escin increased the tone of veins (contracting them due to increased PGF-2) .
Escin also blocked enzymes that break down blood vessel walls, prevented leakage, and maintained the structure of capillaries. Daily escin (1 mg/kg) reduced breakdown of rat tissue over 3 weeks .
4) Horse Chestnut Improves Hemorrhoids
Hemorrhoids are also caused by swollen veins in the anus.
In a study of 80 patients (DB-RCT) with hemorrhoids, escin (40 mg) improved bleeding and swelling in over 80% of patients during two months .
5) Horse Chestnut Reduces Inflammation
In a human study (RCT), escin from horse chestnut (5 mg twice daily, intravenous, 2 weeks) reduced inflammation in 24 women with vein problems. It acts by blocking the release of inflammatory compounds and reducing the activation of immune cells that increase inflammation .
In one study, Kaempferol found in horse chestnut decreased inflammation in the breast cancer cells of mice (by reducing oxidative stress and the activity of immune cells) .
In dog models, the leaves of horse chestnuts have been used to reduce swelling in gum disease .
6) Horse Chestnut May Improve Male Fertility
In a study (RCT) of 219 Chinese male patients with infertility (due to prostate vein swelling) 60 mg of escin for 2 months improved sperm quality, motility, and amount (by at least 30%) .
7) Horse Chestnut Has Anti-aging Effects
Clinical testing of 3% horse chestnut gel on 40 female volunteers (3 times a day, 9 weeks) diminished wrinkles around the eyes compared to the controls .
8) Horse Chestnut Improves Gut Health
In mice, escin increased gut flow and decreased inflammation. Gut flow in mice with paralyzed gut muscles improved with escin supplementation .
9) Horse Chestnut May Reduce Blood Sugar
10) Horse Chestnut May Protect the Kidneys in Diabetes
Diabetic complications can damage the kidneys. In diabetic rats with kidney damage, horse chestnut seed extract reduced inflammation and markers of kidney damage (blood urea nitrogen, and creatinine). Horse chestnuts were capable of restoring kidney function .
11) Horse Chestnut May Fight Cancer
Flavonoids and phenolic acids found in horse chestnut seeds may play a role in fighting cancer.
In pancreatic cancer cells, esculetin blocked the growth of pancreatic cancer. In a brain cell study, the flavonoids quercetin and kaempferol blocked the spreading of a brain tumor that affects children (medulloblastoma) [25, 26].
12) Horse Chestnut is an Antioxidant
In cell studies, escin was a more powerful antioxidant than Vitamin E. The effect of escin is boosted by numerous other antioxidants in the plant .
13) Horse Chestnut May Fight Infections
Caffeic acid found in horse chestnut killed bacteria in a cell study .
14) Horse Chestnut May Protect the Skin
Horse chestnut seed extract protects cells and reduces inflammation, which is linked to anti-aging effects. These qualities, along with escin’s “gentle, soapy feel,” suggest the potential use of horse chestnuts in cosmetics .
Horse Chestnut in Combination with Other Compounds
In rats with colon cancer, horse chestnuts improved the activity of beneficial gut bacteria in combination with a prebiotic and flaxseed oil .
Side Effects and Risks
Horse chestnut seeds need to be properly processed before use. Otherwise, the seeds contain the poison esculetin. Esculetin can cause a headache, nausea, coma, and paralysis .
When prepared correctly, horse chestnuts have few side effects. In some cases, the purified extract can still cause severe skin rash, dizziness, upset stomach, and headache. Horse chestnut damaged red blood cells in rabbits given a high dose for a month (about 10 times greater than the usual dose), but no other toxic effects have been recorded .
Limitations and Caveats
Although many studies proved the benefits of escin for leg vein problems, make sure to speak to a healthcare professional about treatment if you have a venous disease.
Other benefits of escin such as menstrual pain relief do not have studies to back them up. Long-term use has not been evaluated and is not recommended.
Due to lack of research, the use of escin in children, pregnant or breastfeeding women is not recommended.
Since horse chestnut can reduce blood clotting, it can interact with drugs that have a similar effect (ibuprofen, aspirin, naproxen, warfarin, and others) and increase the risk of bleeding .
Horse chestnut may lower blood glucose. In combination with antidiabetic drugs or insulin, this can raise the risk of very low sugar levels (hypoglycemia) .
Horse chestnut dosage depends on the sought-after health benefit.
The maximum oral dose recommended for use in humans per day is 150 mg .
Standardized horse chestnut extracts contain around 20% of escin .
The studied dose for escin injections is 5-10 mg twice daily for up to 2 weeks .
Creams with horse chestnut contain 2% escin and are applied 3-4 times a day up to 2 months .
Forms of Supplementation
Horse chestnut is a herbal supplement that can be purchased as a cream, capsule (dry) or liquid extract.
Today, most horse chestnut extracts are made from the seed as opposed to the leaf or bark since the seed contains the highest concentration of escin .
Some users said horse chestnut seed extract helped them with irregular fat distribution (lipedema) and reduced swelling. However, one user often had nausea and vomiting after taking the supplement.
Most users take horse chestnut with food to avoid stomach upset.
Many users mention that horse chestnuts are effective in reducing varicose veins and leg swelling. Some report leg cramping as a major side effect, as well as chest pain, and headaches.