Rehmannia (Rehmannia glutinosa)
What is Rehmannia?
In my opinion, rehmannia is one of the most useful herbs in the Western herbal dispensary.
It’s popular in Asia for conditions defined as "hot", and is one of the most reliable adrenal tonics available. With so many people succumbing to chronic— often debilitating stress, this class of herbs is extremely valuable.
Hot” conditions— in the perspective of Western herbal medicine could define these conditions as metabolic disorders, involving the endocrine system.
It's considered an adaptogen due to its high level of safety, and ability to modulate the HPA and HPG axis. This has been shown in a variety of animal studies focusing on the effects of rehmannia and its main active constituent catalpol on the hypothalamus, pituitary, and adrenal glands (and associated hormones). This same mechanism of action is responsible for the anti-diabetic and anti-Alzheimer's activity of rehmannia as well.
What Is Rehmannia Used For?
Rehmannia is mainly used for endocrine-related conditions, including diabetes, adrenal fatigue, fevers, asthma, and the suppressive effects of corticosteroid treatment.
Traditional Uses of Rehmannia
+ Traditional Chinese Medicine
In traditional Chinese medicine, cured rehmannia and uncured rehmannia is used differently. Uncured rehmannia is used to reduce fevers and heat conditions, as a haemostatic, to remove heat from the blood, for rashes, diabetes, low grade fevers and for bleeding. [1]. Cured rehmannia on the other hand, was used to regulate mentruation, promote blood production, correct anaeima dizziness, weakness, tinnitus, amenorrhea, and mettorhagia [1].
Fresh Rehmannia:
Added to formulas to tonify yin in the liver, kidney and heart, and add a cooling, anti-inflammatory actions. [4, 6].
Prepared Rehmannia:
Prepared rehmannia is a fundamental kidney tonic in Chinese herbalism and is often associated with longevity. It is a yin jing tonic, and frequently added to formulas designed to strengthen sexual function. [6].
Herb Details: Rehmannia
Botanical Information
Rehmannia is currently listed under the family Orobanchaceae, but there has been a lot of confusion in this area. It's has been included in the families Scrophulariaceae and Gesneriaceae in the past. Many of the Scrophulariacea members were transfered to Plantaginaceae, but not rehmannia.
Rehmannia is a perennial herb growing up to 40 cm in height. The flowers are reddish-purple and tubular in shape. The root is a thick orange tuberous root. [1].
Harvesting Collection, & Preparation
Curing rehmannia (prepared rehmannia) involves washing the fresh root in millet wine, before steaming, and drying several times each. [1]. In Chinese medicine, the prepared version is more highly regarded than fresh rehmannia.
Pharmacology & Medical Research
+ Adrenal Tonic
Not hypertensive like licorice but is toning to the adrenals and may be useful for preventing the suppressive effects corticosteroid drugs. [1].
It appears to antagonize the suppressive effect of glucocorticoids on the hypothalamic-pituitary-adrenal axis (uncured).
Catalpol from rehmannia was shown to increase hydrocortisone levels, and decrease CRH and ACTH in rats with Alzheimer's disease after 7 days [16]. This suggests modulating activity on the HPA axis in neuroendocrine dysregulated organisms.
+ Alzheimer's Disease
Alzheimer's disease is believed to have many causes and contributing factors. One of them being dysfunction of neuroendocrine function [12]. This is due to an increase in glucocorticoids in the blood, resulting in a reduction in corticotropin-releasing hormone (CRH), and neuronal loss in the hippocampus. This ultimately leads to reduced memory and cognitive capacity, promoting the progression of Alzheimer's disease [13].
Studies on mice comparing the effects of catalpol purified from rehmannia and the common anti-Alzheimer's drug donepezil found that catalpol was as effective for reducing biological markers for Alzheimer's disease at a dose of 14mg/day as donepezil at 1.4mg/day. This mechanism of action was noted to be through mechanisms unrelated to antiacetylcholinesterase activity. [14].
Another animal study investigated the role of rehmannias main active constituent, catalpol, on HPA axis function in an Alzheimer's disease rat model. Researchers in this study reported a reduction in elevated hydrocortisone level as well as decreased CRH & ACTH. Structural changes associated with AD were also noted, including an increase in CRHR1 positive neurons. [16].
+ Adaptogenic Effects
The majority of studies on the interaction of rehmannia on glucocorticoids, HPA/HPG interaction, and adrenal function are in vitro or animal research only.
There are no randomized clinical trials available at the time of writing.
In vivo research has suggested HPA axis regulation as a mechanism of action for rehmannias effectiveness on Alzheimer's disease [14]. This is based on earlier research that linked high cortisol levels with Alzheimer's disease through a gradual dysregulation of CRH sensitivity in the hippocampus [13]. Other animal studies supported with results involving changes in essential HPA axis hormones in a neuroendocrine dysregulated rat model of Alzheimer's disease after treatment of a rehmannia extract (catalpol) [16]. Researchers in this study reported a reduction in elevated hydrocortisone (cortisol) levels as well as decreased CRH & ACTH. Structural changes associated with AD were also noted, including an increase in CRHR1 positive neurons. These findings suggest directly modulating activity of rehmannia constituents on the HPA axis.
Other animal studies suggesting HPA or HPG axis modulation in conditions traditionally classified as "yin deficiency" includes diabetes, immunosuppression [15], and bone catabolism [11].
Online sources have suggested inhibition of cortisone metabolism in the liver as a mechanism of action. However, no peer-reviewed research has been found to back up this claim.
Phytochemistry
Rehmannia contains around 31 different iridoid glycosides (including aucubin, catalpol, ajugol, rehmanniosides A-D, jioglutosides, and rehmaglutins A-D), as well as other glycosides such as phenethyl alcohol glycosides (jionosides) ionine glycosides, and terpenoid glycosides, as well as polysaccharides, [1-4, 7-10].
(Catalpol molecule)
Clinical Applications Of Rehmannia:
Rehmannia is useful for conditions involving the HPA and HPG axis.
This herb has a strong modulating activity on this system, useful for supporting a variety of endocrine-related conditions like hypothyroidism, diabetes, GAS, and adrenal fatigue. It's also useful for dementia and Alzheimer's disease through the same effect profile. Its effects on the HPG axis make it useful for low libido, poor fertility, menstrual irregularities, and erectile dysfunction.
It's also useful as an anti-inflammatory and immunomodulator.
Cautions:
Caution is advised in combination with corticosteroid use.
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References:
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Sasaki, H., Nishimura, H., Chin, M., & Mitsuhashi, H. (1989). Hydroxycinnamic acid esters of phenethylalcohol glycosides from Rehmannia glutinosa var. purpurea. Phytochemistry, 28(3), 875-879.
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