Rehmannia (Di-Huang) Root

The roots of this plant have been used in Traditional Chinese and Korean Medicine for over 2,000 years [2, 3].

According to the traditional outlook, the harmony of opposite, but complementary, forces – yin and yang – underlies good health. Rehmannia is thought to help with yin energy imbalances. It is traditionally used to fight bacterial infections, as a tonic, and for a variety of conditions associated with inflammation, like asthma and arthritis [4, 5, 1].

Rehmannia is also often combined with other herbs to remedy “yin deficiency”. For example, it’s one of the six ingredients in a popular Chinese herbal product called Rehmannia Six Formula and one of the seven ingredients in the traditional kidney-nourishing herbal formulation Yukmi-jihang-tang. It is also included in widely-used formulations, such as Liuwei Dihuang Pills [6, 3, 7].

May improve anemia by supporting blood cell production
May support kidney function
Early evidence of mood, blood sugar, and bone support

Although the above-ground parts are sometimes used, herbal remedies are much more often prepared from the orange roots of this plant [8, 9].

Depending on how the roots are prepared, they are called [10]:

Xian-Di-Huang (for the fresh root)
Sheng-Di-Huang (for baked roots)
Shu-Di-Huang (for steamed roots) in Chinese

Over 70 active compounds have been found in Rehmannia, including amino acids, simple and complex sugars, vitamins, and plant-specific compounds. Their composition in extracts mostly varies according to the plant species and the root preparation method [5, 9].

One of the most well-known plant-specific compounds in Rehmannia is called catalpol, which accounts for 0.3-0.5% of the dried root. Catalpol is an iridoid glycoside, a group of molecules plants create to defend against predators. They also have a range of health effects in humans [1, 11, 12].

Catalpol is likely responsible for the plant’s sugar-lowering, inflammation-fighting, and immune-balancing effects in cells and animals. Rehmannia also contains rehmapicrogenin, a strong anti-inflammatory. This compound that helps deactivate one of the most important inflammation-triggering factors in cells (NF-κB) [13, 14].

Mechanism of Effect
According to some researchers, Rehmannia may improve stress resilience and mood by enhancing the body’s antioxidant defense [15].

Certain complex sugars in Rehmannia may target the hippocampus, a part of the brain that plays an important role in memory and mood. Catalpol might also help brain cells resist damage. As a result, the plant’s compounds are currently being investigated for their effect on dementia and anxiety [16, 17, 11].

Rehmannia also affects energy use and is under investigation in people with diabetes and insulin resistance. Sugar extracts of this plant increased insulin production in mice and catalpol lowered glucose levels in diabetic rats. Catalpol also increases the secretion of endorphins from the adrenal gland, which helps transport glucose from the blood into the muscles [18, 19, 20, 21].

Traditional practitioners claim that Rehmannia can reverse anemia, and some evidence suggests that it may protect the parts of the bone marrow that make red blood cells. Nourishing the blood is one of its main traditional indications, while anemia is considered to be a sign of yin deficiency. As such, early sickle-cell anemia clinical trials are in progress with a compound isolated from the steamed roots, but the results aren’t in yet [22, 23].

In cell studies, Rehmannia helped alleviate inflammation by sponging up free radicals – highly reactive compounds that can damage cells – as well as by causing immune cells to secrete fewer inflammatory signaling molecules. Importantly, it also blocked the expression of inflammatory genes in these cell studies. Reducing inflammation is beneficial in many conditions, but researchers are currently looking at its application in bone and kidney health [14, 24, 25, 26, 27, 28].

What’s more, this herb caused kidney cells to express fewer receptors that drive high blood pressure. According to some researchers, if this effect translates to the human body, it could make it useful for protecting the kidneys that are already strained due to other diseases, like diabetes. Dried and steamed roots reduce renin in animals, thereby lowering blood pressure and reducing kidney damage [28, 29].