In Ayurveda, ashwagandha (Withania somnifera, Solanaceae) is considered to be a Rasayana, i.e., a rejuvenator. It has been studied for its effects on cognition, mood, joint health, and inflammation. It contains alkaloids, lactones (withanolides), and glycosides, but it is not clear which constituents account for its adaptogenic qualities. The root is the most used part in traditional practice but leaves also contain many bioactive constituents, so some research has begun to explore the use of ashwagandha leaf. Several recent studies have looked at ashwagandha as an athletic performance enhancer, with encouraging results. In this double-blind, randomized controlled trial, the researchers explored the effect of an aqueous extract of ashwagandha leaf and root (Sensoril; Natreon, Inc.; New Brunswick, New Jersey) on exercise outcomes over a 12-week period. The primary outcome measures changed in upper and lower body muscle strength. Secondary outcome measures were changes in body composition, recovery and mood, muscle endurance and power, and aerobic endurance.
Participants were male, between the ages of 18 and 45, and lived near the study location (the Center for Applied Health Sciences; Stow, Ohio). Eligible participants were healthy and recreationally active, defined as training not more than two to three times per week for the previous six to 12 months. They were required to have a body mass index (BMI) between 20 and 35 kg/m2, have normal blood pressure (≤140/≤90 mmHg), and have a resting heart rate of 90 beats/min or lower. They had not used any performance-enhancing supplements within four weeks before screening. Standard multivitamins were permitted before and during the study.
Over the course of the study, each participant completed four visits. The first visit was a screening interview and blood draw. The second included a practice session so that participants were prepared for the test sessions and to do the prescribed training program without supervision. The third and fourth visits were the before and after points in the study (week 0 and week 12). Each included a battery of exercise tests, a body composition scan, and VAS for five metrics, as well as a blood draw. At the first screening visit, participants completed a 24-hour dietary recall questionnaire. In preparation for visits 3 and 4, they were to eat the same foods that they had eaten in the 24-hour dietary recall, abstain from exercise for 48 hours, and fast for 10 hours prior to arrival. They were to keep a three-day food diary before each of those test sessions to assess the consistency of diet.
Participants were matched based on training experience, baseline body weight, and strength before being randomized into one of two arms. Those in the intervention group received capsules containing 500 mg of an aqueous extract of roots and leaves of ashwagandha, standardized to withanolide glycosides, withaferin A, and oligosaccharides. Those in the placebo group received rice (Oryza sativa, Poaceae) flour capsules packaged by the same company in a blinded fashion. The purity and potency of the ashwagandha capsules were confirmed by an unspecified independent, third-party laboratory. Participants were instructed to take one capsule each morning with 12 ounces of cold tap water.
During the 12-week study period, the participants followed a prescribed four day per week strength training program. Participants received a training log to track workouts, each workout was signed off on by a workout partner or gym staff member, and participants were asked about adherence to the program during weekly phone calls. During these calls, participants were also asked about adverse events (AE), which were recorded and coded.
In testing at weeks 0 and 12, upper body and lower body muscular strength were measured as the 1-repetition maximum (1-RM) in kg for Smith machine bench press and back squat respectively, using National Strength and Conditioning Association protocols. Upper and lower body muscular endurance were measured using 65% of the participant’s 1-RM and reported as a maximum number of repetitions. Upper and lower body power were measured using a TENDO power measuring device and reported in peak watts and average watts of one complete set. Aerobic endurance was measured by time trial using a cycle ergometer. Time to complete 7.5 km at a set difficulty level was reported in seconds. VAS were completed by participants at weeks 0 and 12 for mood, desire to work out, willingness to train, optimism, and soreness.
At initial screening and at weeks 0 and 12, the researchers took venous blood samples and tested for levels of glucose, blood urea nitrogen (BUN), creatinine, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine kinase, lactate dehydrogenase, total bilirubin, alkaline phosphatase (ALP), triglycerides (TG), total cholesterol (TC), low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), high-density lipoprotein (HDL), uric acid, sodium, potassium, total protein, albumin, globulin, iron, complete blood cells, and platelet count. Body composition was analyzed using dual-energy x-ray absorptiometry (DEXA). This machine scans specific body regions and compares lean mass to fat mass. From these findings, the android-to-gynoid ratio was computed using the machine’s software.
Forty participants were recruited; they were aged 26.3±6.7 years old, were 1.80±0.07 m tall, and weighed 87.0±12.8 kg. Initially, 19 were randomized into the Ashwagandha group and 21 into the placebo group; two of the placebo group were lost to follow-up. The placebo group was significantly older than the Ashwagandha group (P=0.04), at 28.6±7.6 years compared to 24.4±4.2 years. There were no significant differences in any of the other baseline measures or in dietary patterns. Overall compliance with supplementation was 81% and with training was 86%.
The ashwagandha group had significantly more improvement than the placebo group in lower body strength (+18.2% vs. 9.7%; P=0.009) and upper body strength (+13.7% vs. +8.2%; P=0.048). Improvements over time in the time trial, average squat power, and peak bench press power were larger in the Ashwagandha group and statistically significant only in that group. The ashwagandha group reported significant improvement in perceived recovery, while the placebo group did not. The ashwagandha group reported much less increase in soreness than the placebo group (+18.0%, not significant, vs +45.6%, P=0.04). None of the other VAS outcomes showed significant change, and no between-group comparisons were significant.
The placebo group had a significant increase in android/gynoid ratio, while the Ashwagandha group had no significant change. During the study there were small statistically significant increases in mean red blood cell count, hemoglobin and hematocrit in the placebo group, increase in creatinine in the Ashwagandha group, and decreases in hemoglobin and albumin in the Ashwagandha group. All “were considered stochastic, and remained within normal clinical limits.” There were no significant changes in either group in other blood tests. There were two AEs among the placebo group (arthralgia in both cases), and three in the intervention group (one each of arthralgia, myalgia, and abdominal pain).
The primary outcome measure increased in strength, and that measure was significantly improved in the Ashwagandha group. This was to be expected, according to the authors, given the known actions of ashwagandha. The many secondary outcome variables suggest several paths for further research. The DEXA finding is unexpected and interesting. The android/gynoid ratio is correlated with the ratio of trunk region fat to hip region fat, which is a marker for metabolic and cardiovascular risk factors. The ashwagandha group saw no significant change in this variable, but the placebo group saw a statistically significant increase. The authors express surprise at this unexpected finding.
The acknowledged limitations include factors that prevented the participants from achieving maximal strength gains, such as their less than optimal protein consumption and performance of exercises without supervision. The study supports the use of ashwagandha for performance enhancement, but the authors suggest that future research explore its effects at the neuromuscular level, as well as documenting effects on biomarkers of chronic inflammation.
Funding for the study was provided by Natreon, Inc., the manufacturer of the tested product. Some of the authors have financial relationships with other supplement companies, but not with Natreon. Data are not publicly available because they are proprietary.
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. November 20, 2018;10(11):1807. doi:10.3390/nu10111807.