Ashwaganda is a supplement that is extracted from the root of the Ashwaganda plant. Ashwaganda (Withania somnifera), also known as Indian Ginseng, is a herb used in the traditional medicine of India (Ayurveda). The root of the ashwaganda plant has a horsey smell and this is also how it received the name ashwa (horse) ghanda (smell).
The herbal extract is often linked with reduced anxiety, improved sleep, and reduced cortisol, as well as strength and endurance performance. Usually when things seem to be good to be true, they are indeed to good to be true. But let’s have a look at this extract and the evidence for recovery or performance (the main reasons athletes would consider it).
The first thing that becomes obvious when screening the scientific literature is that there are very few studies. Most of the studies are very short duration, and also poor quality. As an example let’s look at the study (1) that is often referred to by other papers (because this was the first performance study on ashwaganda). This paper is also included in meta-analyses like the one by Bonilla et al 2021 (2).
Looking at an Ashwaganda study in more detail
The study by Sandhu et al (1) is published in the rather obscure journal “International Journal of Ayurveda Research”. A quick scan of the paper shows many quality issues and even someone with little experience in reviewing papers would very quickly come to the conclusion that this paper should have been rejected in the first round of review (I am making the assumption here, that the paper was actually peer reviewed). The methods section is incomplete with no detail about the methods used (just mention of some machines, but no mention of the processes). There is no mention of what was done to standardise the measurements. No familiarisations were performed. This leaves us with many questions around how the study was conducted. Measurements may not have been performed at the same time of the day. Did the subjects eat in the hour or hours before the trial? Was temperature and humidity controlled? Over what period of time were these measurements performed? It was not a cross-over design. Instead, forty subjects were divided into 4 treatment groups, reducing any statistical power significantly. Many units of measurements are not listed, and the number of decimal places is not related to the accuracy of the measurement. Here are two examples:
Average absolute power = 793.61
What is the unit? Although not mentioned (at least not in the table or text where the numbers are presented), the unit of power is watts (J/s). Can we really measure this to 2 decimal places accurate? We will come back to this point and aften made error in a future blog.
The most important measurement in this study is oxygen uptake. I am copying the full description of the method of measuring oxygen uptake: “Computer controlled Vista Turbo trainer machine was used for evaluating breath by breath gas exchange kinetics. Peak oxygen consumption was measured by using software turbofit version 5.04”. There is so much information missing here. How was it calibrated, how were the numbers that came off the machine verified and calculated into the numbers that are presented?
In any case the reported nu bees are absurd, yet this got published. The reported oxygen uptake values are in ml/kg/min and vary between 10 and 12 ml/kg/min. Who has a VO2peak of 10-14 ml/kg/min? These are values are only slightly above resting values. How can young healthy adults have a VO2max that is just slightly above resting oxygen uptake? This is impossible! And this is the main outcome of the study! A study that is included in a meta-analysis…
And I am not just picking on this one study. In another study subjects received 500mg of a herbal extract every day for 12 weeks (3). The study was randomized, double-blind and placebo-controlled trial. The subjects in this study were recreationally trained. Several strength measurements were performed before and after. There was a statistically significant increase in 1-repetition max for both squat and bench press. However, several other measurements including “the total of all strength measurements” were not significantly different. There is always a bias towards the positive findings and we often ignore the negative findings... but the chance of false positives will always increase with the number of measurements, so the chance that something changes by chance is real.
This study is sometimes cited to demonstrate herbal extract consumption can improve aerobic performance, which was measured with a 7.5 km cycling time trial. However, the findings were not statistically significant and looking at the times, on average more than 20 min (or roughly 22km/h), it raises many questions about the time trial and/or the participants. For many healthy individuals it would be pretty difficult to ride that slow.
What can we conclude about ashwaganda and performance?
Overall, evidence that ashwaganda has any effects on strength or endurance is at least sketchy. Well controlled studies need to be performed before we can draw conclusions about the efficacy of ashwaganda. In the meantime, marketing of supplement companies will keep referring to studies like the one mentioned here, and people will keep buying the supplements in the hope that their VO2max will also be improved from 13.54 to 14.47 ml/kg/min. This would be the difference between a very slow walk and a very slow walk measured with an impossible accuracy.
Sandhu JS, Shah B, Shenoy S, Chauhan S, Lavekar GS, Padhi MM. Effects of Withania somnifera (Ashwagandha) and Terminalia arjuna (Arjuna) on physical performance and cardiorespiratory endurance in healthy young adults. Int J Ayurveda Res. 2010 Jul;1(3):144-9.
Bonilla DA, Moreno Y, Gho C, Petro JL, Odriozola-Martínez A, Kreider RB. Effects of Ashwagandha (Withania somnifera) on Physical Performance: Systematic Review and Bayesian Meta-Analysis. J Funct Morphol Kinesiol. 2021 Feb 11;6(1):20.
Ziegenfuss TN, Kedia AW, Sandrock JE, Raub BJ, Kerksick CM, Lopez HL. Effects of an Aqueous Extract of Withania somnifera on Strength Training Adaptations and Recovery: The STAR Trial. Nutrients. 2018 Nov 20;10(11):1807.