The Importance of Using the Correct Plant Part: The Case for Withania Root
Herbal medicine is the oldest form of medicine used by humans, utilised by all cultures throughout the ages since time immemorial.1 When used appropriately, herbs can be wonderful medicines. To ensure that the herbs you are using are as safe and efficacious as possible, it is vital to use both the correct plant species and the correct plant part. Closely related species can have vastly different effects in the body, and even different parts of the same plant can have different effects.2 In some cases, certain parts of the plant are beneficial or even medicinal, while other parts of the same plant are toxic. The humble potato is a good example of this concept: the underground tuber is both delicious and nutritious, while all other parts of the plant are toxic.3 Unfortunately in some cases, it is not always completely clear or obvious which plant part to use. Sometimes the plant part used in modern herbal preparations and clinical studies can vary. Withania (Withania somnifera) is a good example of this. Most Withania preparations contain only the root, but some are made from the whole plant, and others from the leaves alone.4 So which is the correct plant part to use, and does it really matter? There are several factors involved when considering these questions.
Traditional Use
The traditional use of a herb is an important layer of evidence. Withania has been widely used in Ayurveda and Unani, the traditional medicine systems of India, for centuries. Here, it is known as Ashwagandha, and is revered as a rasayana or rejuvenating tonic.5 Traditionally, different parts of the plant have been used for different purposes. The root is the primary part used orally for its tonic, sedative, anti-inflammatory and pain relieving effects. The leaves and aerial parts have traditionally been used topically almost exclusively, for their astringent and cytotoxic effects. The leaves are only used orally for a few select conditions, such as helminth infection, fever and certain cancers.5,6
Official Pharmacopoeias
The World Health Organisation (WHO) guidelines recommend referring to standard references such as official pharmacopoeias when assessing the quality, safety, efficacy and intended use of a herbal medicine.7 The American Herbal Pharmacopoeia,8 Siddha Pharmacopoeia of India,9 Unani Pharmacopoeia of India,10 the Health Canada monograph,11 and the World Health Organization’s monograph12 all list the root alone as the correct plant part for Withania.
Phytochemical Profile
Different parts of the same plant can have vastly different phytochemical profiles. The phytochemical profile of Withania roots is quite different from the leaves. The leaves have significantly higher concentrations of the total active metabolites with 228 mg/g (22.8%) in the leaf versus 15 mg/g (1.5%) in the roots.13 While some may say that indicates the leaves are more active, more is not always better. The active metabolites of Withania include alkaloids, which are powerful substances that can be toxic in high doses.14 The leaves of Withania contain a particularly high level of the metabolite Withaferin A, at 22.3 mg/g (2.23%). The Withaferin A content is significantly lower in the roots, at 0.92 mg/g (0.09%).13 Withaferin A has been well researched in recent times for its cytotoxic effects.4 While this may explain the traditional use of the leaves in cancer, the cytotoxic effects are not beneficial for healthy cells or desirable for healthy people. Hence, the root should be the preferred part for oral use.
Clinical Trials
Human clinical trials are the gold standard of evidence for therapeutic substances. Over 30 human clinical trials have been conducted on Withania root to date, which have demonstrated clinical efficacy in a range of conditions such as chronic stress, anxiety, insomnia, hypothyroidism, rheumatoid arthritis, male and female infertility, and type 2 diabetes.15 Only a small number of human studies have utilised the whole plant or the root plus leaves, and very few have been conducted on the leaf alone.16,17 The strength of evidence clearly supports Withania root rather than the leaf or whole plant.
Safety Studies
Safety is an important consideration for any therapeutic substance, including herbal medicines. As evidenced by the potato, not all parts of a particular plant are equal when it comes to safety. No serious adverse effects have been reported in the relatively large body of human trials conducted on Withania root, with only mild transient side effects such as drowsiness and gastrointestinal upset reported. Specific human safety studies on Withania root have found no changes to haematological and biochemical markers, and no adverse effects. Safety studies conducted in animals have also demonstrated no toxicity and no reproductive toxicity when Withania root is given orally at doses up to 2000 mg/kg.15,17 Even very high doses of Withania root extract given by injection have shown limited toxicity.15 Both human and animal safety studies on other parts of the Withania plant are lacking.17
Traditional Wisdom and Modern Science Agree
Appropriate herbal prescribing not only involves selecting the right herbs, but also the right herb parts. In the case of Withania, both traditional wisdom and modern scientific studies support the use of the root alone for safe, efficacious herbal prescribing.
References
1. Kunle, Oluyemisi F, Egharevba, Henry O, Ahmadu, Peter O. Standardization of herbal medicines-A review. Int J Biodivers Conserv. 2012 Mar 31;4(3):101-12. DOI: 10.5897/IJBC11.163
2. Adams J, Tan E. Herbal manufacturing. Preston: Northern Melbourne Institute of TAFE printers;2006
4. Mukherjee PK, Banerjee S, Biswas S, Das B, Kar A, Katiyar CK. Withania somnifera (L.) Dunal - Modern perspectives of an ancient Rasayana from Ayurveda. J Ethnopharmacol. 2021 Jan 10;264:113157. https://doi.org/10.1016/j.jep.2020.113157
5. Rayees S, Malik F. Withania somnifera: from traditional use to evidence based medicinal prominence. Science of Ashwagandha: Preventive and therapeutic potentials. 2017:81-103.
6. Paul S, Chakraborty S, Anand U, Dey S, Nandy S, Ghorai M, et al. Withania somnifera (L.) Dunal (Ashwagandha): A comprehensive review on ethnopharmacology, pharmacotherapeutics, biomedicinal and toxicological aspects. Biomed Pharmacother. 2021 Nov;143:112175. https://doi.org/10.1016/j.biopha.2021.112175
7. Akerele O. WHO guidelines for the assessment of herbal medicines. Fitoterapia. 1992 Nov;63(2):99-110. Available from https://apps.who.int/iris/bitstream/handle/10665/58865/WHO_TRM_91.4.pdf?sequence=1
8. American Herbal Pharmacopoeia and Therapeutic Compendium. Ashwagandha root: Withania somnifera analytical, quality control, and therapeutic monograph [Internet]. Santa Cruz: American Herbal Pharmacopoeia; 2000 [cited 2023 Aug 8]. 25 p. Available from: https://herbal-ahp.org/online-ordering-ashwagandha-root/
9. Government of India, Ministry of Health and Family Welfare, Department of AYUSH. The Siddha pharmacopoeia of India. Part – I. Volume – I. First Edition [Internet]. New Delhi: Government of India, Ministry of Health and Family Welfare, Department of AYUSH; 2008 [cited 2023 Aug 8]. 389 p. Available from: https://perpus.univpancasila.ac.id/repository/EBUPT181123.pdf
10. Government of India, Ministry of Health and Family Welfare, Department of AYUSH. The Unani pharmacopoeia of India. Part – I. Volume – I [Internet]. New Delhi: Government of India, Ministry of Health and Family Welfare, Department of AYUSH; 2007 [cited 2023 Aug 8]. 237 p. Available from: http://t27.ir/Files/121/Library/5371af74-77d5-4687-b2b6-e052d3b2627a.pdf
11. Government of Canada, Health Canada. Health Canada monographs. Ashwagandha: Withania somnifera. [Internet] Government of Canada; 2019 [cited 2023 Aug 14]. Available from: https://webprod.hc-sc.gc.ca/nhpid-bdipsn/monoReq.do?id=35
12. World Heath Organisation. WHO monographs on selected medicine plants Volume 4. Radix Withaniae. [Internet] Geneva: WHO Press; 2009 [cited 2023 Aug 14] Available from: https://apps.who.int/iris/bitstream/handle/10665/42052/9789241547055_eng.pdf?sequence=4&isAllowed=y
13. Chatterjee S, Srivastava S, Khalid A, Singh N, Sangwan RS, Sidhu OP, et al. Comprehensive metabolic fingerprinting of Withania somnifera leaf and root extracts. Phytochemistry. 2010 Jul;71(10):1085-94. https://doi.org/10.1016/j.phytochem.2010.04.001
14. Heinrich M, Barnes J, Gibbons S, Williamson EM. A text book of Fundamentals of Pharmacognosy and Phytotherapy. Elsevier, USA. 2004.
15. Tandon N, Yadav SS. Safety and clinical effectiveness of Withania Somnifera (Linn.) Dunal root in human ailments. J Ethnopharmacol. 2020 Jun 12;255:112768. https://doi.org/10.1016/j.jep.2020.112768
16. Saleem S, Muhammad G, Hussain MA, Altaf M, Bukhari SNA. Withania somnifera L.: Insights into the phytochemical profile, therapeutic potential, clinical trials, and future prospective. Iran J Basic Med Sci. 2020 Dec;23(12):1501-26. https://doi.org/10.22038/IJBMS.2020.44254.10378
17. Speers AB, Cabey KA, Soumyanath A, Wright KM. Effects of Withania somnifera (Ashwagandha) on Stress and the Stress- Related Neuropsychiatric Disorders Anxiety, Depression, and Insomnia. Curr Neuropharmacol. 2021;19(9):1468-95. https://doi.org/10.2174/1570159X19666210712151556
