Eﬀects of Ashwagandha (Withania somnifera) on
VO2max: A Systematic Review and Meta-Analysis
Jorge Pérez-Gómez 1, Santos Villafaina 2,* , JoséCarmelo Adsuar 1,
Eugenio Merellano-Navarro 3and Daniel Collado-Mateo 4
1HEME Research Group, Faculty of Sport Sciences, University of Extremadura, 10003 Caceres, Spain;
firstname.lastname@example.org (J.P.-G.); email@example.com (J.C.A.)
2Physical Activity and Quality of Life Research Group (AFYCAV), Faculty of Sport Science, University of
Extremadura, 10003 Cáceres, Spain
3Facultad de Educación, Universidad Autónoma de Chile, Talca 3460000, Chile; firstname.lastname@example.org
4Centre for Sport Studies, Rey Juan Carlos University, Fuenlabrada, 28943 Madrid, Spain;
*Correspondence: email@example.com; Tel.: +34-927-257-460
Received: 15 March 2020; Accepted: 14 April 2020; Published: 17 April 2020
The purpose of this study was to systematically review the scientiﬁc literature about the
eﬀects of supplementation with Ashwagandha (Withania somnifera) on maximum oxygen consumption
), as well as to provide directions for clinical practice. A systematic search was conducted
in three electronic databases following the Preferred Reporting Items for Systematic Reviews
and Meta-Analyses Guidelines (PRISMA). The inclusion criteria were: (a) VO
standard deviation before and after the supplement intervention, (b) the study was
randomized controlled trial (RCT), (c) the article was written in English. The quality of evidence was
evaluated according to the Grading of Recommendations, Assessment, Development and Evaluation
(GRADE) approach. A meta-analysis was performed to determine eﬀect sizes. Five studies were
selected in the systematic review (162 participants) and four were included in the meta-analysis
(142 participants). Results showed a signiﬁcant enhancement in VO
in healthy adults and
athletes (p=0.04). The mean diﬀerence was 3.00 (95% CI from 0.18 to 5.82) with high heterogeneity.
In conclusion, Ashwagandha supplementation might improve the VO
in athlete and non-athlete
people. However, further research is need to conﬁrm this hypothesis since the number of studies is
limited and the heterogeneity was high.
Keywords: ergogenic aids; maximum oxygen consumption; performance sports; physical ﬁtness
Maximum oxygen consumption (VO
) is a physiological parameter that deﬁnes the aerobic
capacity of a person. It is an indicator of the cardiorespiratory ﬁtness that describes health status [
sport performance [
]. Focusing on competitive sports, the VO
, together with running economy
and the anaerobic threshold, is one of the main factors that determine success in endurance activities [
and also contributes to increase the team sports performance by increasing work intensity, distance
covered, and number of sprints completed [
]. However, from the point of view of the physical training,
there are still controversies about the best training intensity to enhance the VO2max [5,6].
Apart from sport performance, VO
has special interest in the ﬁeld of health. Low values of
) are associated with an increased risk of mortality and loss of independent
lifestyle in adults and elderly [
], while high values of cardiorespiratory ﬁtness have been associated
with a reduced risk of cardiovascular diseases [
]. The VO
level is also important in children,
where a higher aerobic capacity is related to better quality of life .
Nutrients 2020,12, 1119; doi:10.3390/nu12041119 www.mdpi.com/journal/nutrients
Nutrients 2020,12, 1119 2 of 11
Ashwagandha (Withania somnifera) is a plant in the Solanaceae family. The extract of the
Ashwagandha root has many biological implications due to its diverse phytochemicals [
], so it
has been used, singly or in combination with other natural plants, in many research studies for its
properties: anti-diabetic [
], anti-inﬂammatory [
], anti-microbial [
], anti-tumor [
], anti-stress [
], or neuroprotective [
]. It also displays enhanced endothelial function [
reduces reactive oxygen species [
], regulates apoptosis [
], and modulates mitochondrial
], showing to be eﬀective to treat aging eﬀects [
], anxiety and stress [
], arthritis [
cognitive functions and memory [
], diabetes [
], epilepsy [
], fatigue [
diseases , pain , thyroid function , and skin diseases .
In spite of the relevant beneﬁts of supplementation with Ashwagandha, only four meta-analyses
have been carried out evaluating its eﬃcacy on anti-inﬂammatory eﬀects [
], on impotence and
infertility treatment [
], on neurobehavioral disorders [
] and anxiety [
]. However, there are no
meta-analyses that analyze the eﬀect of Ashwagandha on physical performance. Therefore, the purpose
of this study was to systematically review the scientiﬁc literature about the eﬀects of supplementation
with Ashwagandha on VO
and to provide practical recommendations. Besides, a meta-analysis
was carried out to determine the eﬀect sizes of Ashwagandha on VO2max.
The review was conducted following the statements of the Preferred Reporting Items for Systematic
Reviews and Meta-Analyses Guidelines (PRISMA).
2.1. Literature Search
To ﬁnd the studies reported in the meta-analysis, several electronic databases were screened:
PubMed (Medline), Web of Science (which includes other databases such as Current Contents Connect,
Derwent Innovations Index, Korean Journal Database, Medline, Russian Science Citation Index, and
Scielo Citation Index) and Google Scholar. The search was conducted in September 2019. The search
terms were: (a) the type of treatment (Ashwagandha or “withania somnifera”) and (b) the outcome
variable (“oxygen consumption” or “aerobic” or “VO
”). The search was conducted using the treatment
and the outcome variables, separated by the Boolean operator “and”.
2.2. Study Selection
The inclusion criteria were: (a) VO
data, with means
standard deviation (SD) before and
after the supplement intervention; (b) the study was a randomized controlled trial (RCT); (c) the article
was written in English. Two independent authors selected the potentially eligible articles from the
databases. There were no disagreements.
2.3. Quality of the Evidence and Risk of Bias
The quality of the evidence was categorized using the Grading of Recommendations, Assessment,
Development and Evaluation (GRADE) approach. The risk of bias was assessed by the Cochrane
Collaboration’s tool for assessing risk of bias. This tool classiﬁed the selection, performance, detection,
attrition, and reporting bias into low, high, or unclear risk of bias.
2.4. Data Collection
Two authors independently extracted data from the studies. The information included: participants,
interventions, comparisons, outcomes, and study design (PICOS), following the recommendations
from the PRISMA statement. Table 1shows age, sex, sample size, and condition of the participants.
Table 2presents intervention and the comparison groups, including type of supplementation with the
doses, duration of the study, and the daily frequency of the supplementation. Figure 3 displays results
for the diﬀerent outcomes. Study design was not included in any table because all studies were RCT.
Nutrients 2020,12, 1119 3 of 11
Table 1. Characteristics of the sample.
RCT Weeks Groups,
Sample Size and Sex Age (Years) Country Population
Shenoy 2012 8 AS: 20 (M and F)
CG: 20 (M and F) 18–27 India Elite cyclists
Malik 2013 8 AS: 16 (M)
CG: 16 (M) 16–19 India Hockey players
Choudhary 2015 12 AS: 25 (M and F)
CG: 25 (M and F) 20–45 India Athletes
Tripathi 2016 2 AS: 10 (M)
CG: 10 (M) 18–45 India Healthy adults
Sandhu 2010 8 AS: 10 (M and F)
CG: 10 (M and F) 18–25 India Healthy adults
RCT: randomized controlled trial; AS: Ashwagandha group; M: males; F: females; CG: control group.
Table 2. Characteristics of the interventions.
Ashwagandha Group Control Group Dose
Shenoy 2012 Ashwagandha in
starch powder 500 8 weeks twice 56
Malik 2013 Roots of WS
Sugar power was
ﬁlled in gelatin
500 8 weeks once 28
One capsule of KSM-66
containing sucrose 300 12 weeks twice 50.4
WS aqueous extract in
the capsule form Maize starch capsule 330 2 weeks once 4.62
Sandhu 2010 WS ﬁlled in gelatin
Capsules ﬁlled with
ﬂour 500 8 weeks once 28
RCT: randomized controlled trial; KSM-66: commercial name of an Ashwagandha extract; WS: Withania Somnifera.
Total dose was calculated as: total dose (g) =(dose (mg) ×daily frequency ×study duration (days))/1000.
2.5. Statistical Analysis
The main outcome of this meta-analysis was VO
. The meta-analysis was conducted using
the Revision Manager (RevMan) software (version 5.3) obtained from Cochrane Collaboration web.
Post-intervention mean and SD were extracted and used for meta-analyses. All articles reported VO
max as mL/kg/min. Mean diﬀerence was calculated using a random model. The heterogeneity between
the studies was calculated using Tau
, and Chi
tests. Although there is no consensus about the
deﬁnition of “mild”, “moderate”, or “severe” heterogeneity, Higgins and Thompson [
that values for I
higher than 56% would mean large heterogeneity while values lower than 31% would
be related to low heterogeneity.
3.1. Study Selection
The PRISMA ﬂow diagram is showed in Figure 1. A total of 129 records were identiﬁed, 9 of
which were removed because they were duplicated. Of the remaining 120 articles, 92 were excluded
because they were not related with the topic, 4 studies were not written in English, and 4 were reviews.
After reading the remaining 20 articles, another 15 studies did not meet the inclusion criteria and were
excluded. Therefore, 5 studies were included in the systematic review. However, the article by Sandhu
et al. [
] was excluded from meta-analysis due to the odd results. In this regard, they evaluated
healthy young males and females aged between 18 and 25 with body mass index between 18 and 25.
Their mean peak VO
was lower than 14mL/kg/min, which is so much lower than expected for
healthy young people and less than half the mean of the rest of the included studies (46.18 mL/kg/min).
Nutrients 2020,12, 1119 4 of 11
We tried to contact with the authors in order to obtain a reason for that, but at the time this article was
considered for publication, we did not receive a response. Considering that in the article authors did
not explain an incremental test to obtain the VO
, we believe that they measured the gas exchange
at rest, reporting the oxygen consumption (VO
). Therefore, this article was included in systematic
review but not in the meta-analysis.
Figure 1. Flow chart delineating the complete systematic review process.
3.2. Quality of Evidence and Risk of Bias
The evidence of the eﬀects on VO
was initially classiﬁed as “high quality” due to all the
selected articles were RCT, but the evidence dropped twice because of the small sample size and due
to the high degree of heterogeneity. Therefore, the ﬁnal quality of the evidence was low. The Cochrane
Collaboration’s tool for assessing risk of bias (Figure 2) showed that the poorer scores were obtained in
the performance and detection bias due to unclear reporting.
3.3. Study Characteristics
Study characteristics are summarized in Table 1. The total number of participants included in this
systematic review were 162. Of these, 81 belonged to the Ashwagandha group and 81 were the placebo
(control) group. The age ranged from 16 to 45 years old. The sample was comprised exclusively of
healthy adults and athletes.
Nutrients 2020,12, 1119 5 of 11
Figure 2. The Cochrane Collaboration’s tool for assessing risk of bias.
The characteristics of the Ashwagandha supplementation and placebo group are displayed in
Table 2. The doses varied from 300 to 500 mg and the daily frequency intake was once or twice a day.
The total duration of the intervention varied from 2 to 12 weeks.
3.5. Outcome Measures
The study of Choudhary et al. [
] found a signiﬁcant group*treatment interaction in the VO
The remaining four articles only found within-group improvement in VO
after the supplement
Regarding meta-analysis results, a signiﬁcant (p=0.04) mean diﬀerence was observed. Figure 3
showed a mean diﬀerence of 3.00 (95% CI from 0.18 to 5.82). The heterogeneity level was large
according to the I
=84%. The quality of the evidence was low according to the GRADE classiﬁcation.
Nutrients 2020,12, 1119 6 of 11
Figure 3. Meta-analysis results of the eﬀects of Ashwagandha supplementation on VO2max.
Nutrients 2020,12, 1119 7 of 11
The purpose of this study was to systematically review the scientiﬁc literature about the eﬀects of
supplementation with Ashwagandha on VO
and to carry out a meta-analysis to determine the
overall eﬀect. After 20 articles were assessed for eligibility, 15 articles were excluded since they did not
. A total of 5 articles were included in the systematic review [
]. However, one article
was excluded from the meta-analysis [
] since the reported mean VO
was abnormally low for
healthy young people and less than half the mean of the rest of the included studies (46.18 mL/kg/min),
which may indicate that they were not actually reporting VO
at rest. The results of this
meta-analysis showed that supplementation with Ashwagandha may be useful to improve VO
] and healthy adults [
]. Table 2displayed the amount of Ashwagandha used in
each study, which varied from 330 up to 1000 mg/day, which is inside the limits, 750 to 1250 mg/day,
found to be well tolerated and safe . In this regard, none of the ﬁve articles reported any relevant
side eﬀect as a consequence of the treatment, achieving a high compliance with the treatment and very
low number of dropouts.
The two studies that achieved the highest treatment eﬀect and eﬀect size [
] were those with
the highest Ashwagandha intake (>50 g in the whole program). Therefore, it seems like the higher the
dose, the higher the improvement in VO
. However, the study by Tripathi, Shrivastava, Ahmad Mir,
Kumar, Govil, Vahedi, and Bisen [
] did not observe any signiﬁcant diﬀerence between the eﬀects of a
330 mg intake and the eﬀects of a 500 mg intake after 2 weeks. Therefore, further studies comparing
the eﬀect of diﬀerent doses, as well as studies with longer duration are needed.
In general terms, the overall eﬀects were better in those studies with a sample comprised of
] compared with the studies with healthy adults [
]. This is interesting since, as
expected, baseline levels were higher in athletes and, consequently, larger improvements were expected
in non-athlete healthy adults. It could be that the eﬀects of supplementation with Ashwagandha might
be linked to the physical activity levels of the participants, promoting and increasing the physiological
adaptations to physical exercise. However, this hypothesis should be explored in future studies.
deﬁnes the body’s ability to transport and utilize oxygen, so this physiological parameter
is associated with endurance performance. Many factors contribute to the VO
genetic predisposition [
], enzymes [
], muscle ﬁber type [
], or training [
]. It is also known that
nutritional supplementation can improve the eﬀects of training and reach higher performance [
Previous studies with Ashwagandha administration observed improvement in working capacity test
in rats by increasing the swimming endurance test [
]. As endurance performance is determined
by mitochondrial function, some reasons for the Ashwagandha to improve cardiorespiratory ﬁtness
can be the signiﬁcant eﬀects observed on mitochondrial and energy levels, by reducing the succinate
dehydrogenase enzyme activity in the mitochondria and beneﬁting Mg-ATPase activity [
studies showed that Ashwagandha signiﬁcantly enhanced the hemoglobin concentration and red blood
cells in animals [
] and also in humans [
], with the subsequent increase in the capacity to transport
oxygen to the muscles. Moreover, it should be considered that Ashwagandha has shown to have
] and anti-stress [
] actions. This could be connected to the signiﬁcant improvement
in the time to exhaustion of the experimental group that could be observed in the study of Shenoy,
Chaskar, Sandhu, and Paadhi [
]. Some of the chemical constituents of Whitania somnifera [
] such as
ﬂavonoids, alkaloids, and steroidal lactones (withanolides) or the antioxidants (superoxide dismutase,
catalase, and glutathione peroxidase) could be behind the improvements of VO
. Therefore, further
studies are needed to explore which are the chemical constituents and mechanism that may explain
the potential improvement in the VO2max.
Although all mechanisms by which Ashwagandha can improve the VO
have not been
described yet and future studies are needed to elucidate that improvement, it is known that
Ashwagandha exhibits little or no associated toxicity [
], so it seems that this Ayurvedic herb
“Ashwagandha” (Withania somnifera) can be safely used for improving cardiovascular ﬁtness in healthy
Nutrients 2020,12, 1119 8 of 11
adults and also in athletes, oﬀering an additional alternative as a nutritional supplement to enhance
Some limitations in the present meta-analysis can be mentioned. The ﬁrst one is related to the
search strategy, only articles published in English were included and a few databases were used.
Another limitation can be the large heterogeneity in the included articles. Diﬀerent doses, levels of
physical activity, or the inclusion of both women and men in the protocols make it very diﬃcult
to achieve a high level of evidence. In addition, the systematic review and meta-analysis was not
prospectively registered in any public database. Furthermore, in order to have a better understanding
of long-term ergogenic beneﬁt and potential side eﬀects from Ashwagandha root extract, longer
duration studies are needed.
Ashwagandha supplementation might improve the VO
in athlete and non-athlete people.
The analyzed studies used oral administration of Ashwagandha which varied between 2 and 12
weeks with intakes between 300 to 1000 mg/day. Due to the limited number of studies included in
this systematic review and meta-analysis, further research is needed to conﬁrm the eﬀects and the
Conceptualization, J.P.-G., J.C.A. and D.C.-M.; methodology, J.P.-G., S.V., E.M.-N. and
D.C.-M.; software, J.C.A., and D.C.-M.; formal analysis, J.P.-G., S.V., J.C.A., E.M.-N., and D.C.-M.; investigation,
J.P.-G., S.V., J.C.A., E.M.-N., and D.C.-M.; data curation, J.P.-G., J.C.A. and S.V.; writing—original draft preparation,
J.P.-G., S.V. and D.C.-M.; writing—review and editing, J.P.-G., S.V., J.C.A., E.M.-N. and D.C.-M.; supervision, J.P.-G.,
S.V., J.C.A., E.M.-N. and D.C.-M. All authors have read and agreed to the published version of the manuscript.
S.V. is supported by a grant from the regional Department of Economy and Infrastructure of the
Government of Extremadura and European Social Fund (PD16008).
Conﬂicts of Interest: The authors declare no conﬂict of interest.
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