Effects of Withania somnifera on Reproductive System: A Systematic Review of the Available Evidence

Introduction Withania somnifera (WS) also known as ashwagandha is a well-known medicinal plant used in traditional medicine in many countries for infertility treatment. The present study was aimed at systemically reviewing therapeutic effects of WS on the reproductive system. Methods This systematic review study was designed in 2016. Required data were obtained from PubMed, Scopus, Google Scholar, Cochrane Library, Science Direct, Web of Knowledge, Web of Science, and manual search of articles, grey literature, reference checking, and expert contact. Results WS was found to improve reproductive system function by many ways. WS extract decreased infertility among male subjects, due to the enhancement in semen quality which is proposed due to the enhanced enzymatic activity in seminal plasma and decreasing oxidative stress. Also, WS extract improved luteinizing hormone and follicular stimulating hormone balance leading to folliculogenesis and increased gonadal weight, although some animal studies had concluded that WS had reversible spermicidal and infertilizing effects in male subjects. Conclusion WS was found to enhance spermatogenesis and sperm related indices in male and sexual behaviors in female. But, according to some available evidences for spermicidal features, further studies should focus on the extract preparation method and also dosage used in their study protocols.


Introduction
Infertility is a complicated problem with physiologic, psychologic, and economic aspects. Infertility is defined as the inability to conceive after one year of unprotected sexual intercourse [1]. About 15 percent of couples worldwide suffer infertility [2]. One in six couples is involved with infertility during their reproductive age. Based on World Health Organization report, 60-80 million couples suffer from failure of fertility worldwide [3]. It may be difficult to diagnose the reason for infertility but it may include either dysregulation of sex hormonal axis in both men and women or anatomical anomalies [4]. According to different studies, approximately 20%-50% of infertility is due to male, 40% is due to female factors, and 25% of causes are unknown [1,5].
The causes of male infertility are classified as pretesticular, testicular, posttesticular, and unknown. Sperm abnormality causes 30%-40% of all infertility [6]. Pretesticular causes include disorders in the hypothalamus-pituitary-gonadal axis, systemic diseases, sexual dysfunction, and psychopathy. Testicular dysfunction due to multiple reasons as infection, trauma, varicocele, cryptorchidism, chromosomal anomalies, alcohol, cigarettes, drugs, and radiation is another cause of male infertility. Posttesticular disorders comprise the abnormalities in sperm transfer such as obstruction or dysfunction of epididymis and ductus deferens, immunological defects, and anatomical abnormalities like hypospadias [7,8].
Different etiologies of female infertility include ovarian diseases, tubal disorders, endometriosis, uterine pathologies, cervical problems, congenital anomalies, and dysfunction of the hypothalamus-pituitary-ovarian axis and systemic diseases [1,9]. Treatment of infertility may vary due to the different etiologies but it ranges from simple pharmacological treatments to advanced laboratory procedures and surgeries. In developing countries, due to the lack of adequate equipment to diagnosis and treatment for many infertility causes and also probable long-term diagnosis process, many people tend to use alternative and complementary medicine [10]. Herbal medicines are one of the main modalities used in this field.
Withania somnifera, (WS) also known as ashwagandha, Indian ginseng, winter cherry, horse smell, Kaknaje Hindi, is a well-known medicinal plant in Solanaceae family used in traditional medicine in many countries such as Iran and India [11]. This plant is known to cure impotency and increase sex appeal and fertility when used solitarily or in combination with other medications [12,13]. This wild plant grows in dry and hot-semiarid climate such as southern Mediterranean region, Canary Islands, and northern Africa to northern India (Iran, Jordan, Sudan, Palestine, Afghanistan, and Egypt) [14,15]. Different parts of this plant such as roots, leaves, flowers, seeds, stems, and fruits are used as remedy in traditional medicine of different countries [16][17][18]. Many phytochemicals have been extracted so far from this plant with possessing different pharmacologic and biological properties [19].
WS has been recommended for management of polyarthritis, lumbago, painful swellings, premature ejaculation, oligospermia, plague, asthma, vitiligo, general debility, impotency, ulcers, uterine infection, leucorrhoea, hemorrhoid, and orchitis in traditional Persian medicine [60,61]. All these therapeutic uses suggest its anti-inflammatory, aphrodisiac, semenogogue, and deobstruent features [62][63][64][65]. As far as there are no wide-spectrum and specific studies or systematic reviews about therapeutic effects of WS, on male and female reproductive system, the present study was trying to systemically review therapeutic effects of WS on reproductive system and fertility disorders.
To search for unpublished articles (grey literature), European Association for Grey Literature Exploitation (EAGLE) and Health Care Management Information Consortium (HMIC) were searched.

Articles Evaluation.
The selected papers extracted from the databases were assessed by two investigators using Consort 2010 checklist. Discrepancies between the two raters were referred to the third investigator. First, the titles of all articles were reviewed to screen for eligibility and those found to be irrelevant with the objectives of the study were excluded from the study. In the later stages, the abstracts and full-text articles were, respectively, examined to identify and exclude those that did not match the inclusion.

Data Extraction.
One reviewer extracted the data from the included studies while a second author checked the results. Any disagreements were resolved by a discussion of reviewers. Data for the primary objective of the review was collected from the full text of each publication and included the trial name, year of publication, type of study, sample size, results, and other characteristics.

Statistical
Analysis. Statistical analysis was performed by SPSS software package version 16.0 for windows (SPSS Inc., Chicago, USA) [66]. Quantitative data are presented as mean ± standard deviation (SD), while qualitative data are demonstrated as frequency and percent (%).

Results
The flowchart of the study is shown in Figure 1. Of 459 recognized studies, 42 studies were included in the present study. These studies were composed of 8 human studies (7 studies on men and one among women), 28 animal studies (20 studies of male animals and 8 studies on female animals), 5 animal-cellular studies, and one cellular study. In these studies, roots (29 studies), leaves (7 studies), fruits (2 studies), unknown extract (2 studies), and stems (1 study) were used. Characteristics and results of human, animal, and animalcellular studies are shown in Tables 1, 2, and 3, respectively. In all human studies, root extract was used. The duration of human studies ranged from 60 to 90 days. Mostly the WS extract was used orally and once daily in 50 percent of human studies. In the most studies, no side effects were found for WS extract during of studies [17,20,21,30,36,40,45,46,58].
In a study by Shukla et al. about effects of WS on men, WS root powder was used for 3 months and it was shown that sperm parameters such as count and motility in sperm analysis had improved due to decrease apoptosis and reactive oxidative stress among men with normospermia and oligospermia; also copper, zinc, iron, and gold ions of seminal plasma had increased after the treatment and subsequently semen quality increased. This increase in semen quality is proposed to be due to the increase in essential neurotransmitters, metallothionein which has antioxidative function, and metal ions as cofactors for essential enzymes [23].
In two clinical trials, the effects of 5 grams of WS root for 3 months on semen parameters of infertile men were investigated. Improvement in semen quality, increased vitamins E, C, and A, and increased fertility were reported which is proposed to be due to the high amount of alkaloids, ergostane steroids, and essential amino acids in WS which improved detoxification, decreased oxidative stress, and restorated testosterone secretion [12,25].
In another human study, treatment by WS aqueous extract in married healthy women increased their sexual function index and diminished sexual distress index statistically significant [21]. In two studies using WS root extract for men with psychologic erectile dysfunction, there was no statistically significant difference between the intervention and control group considering sexual function indices [22,26]. Also, WS root extract was found to decrease prolactin level after 3 months of administration among infertile men [12,24,25].
In a study by Bhattarai et al. about effects of WS root extract, it was found that GABA mimetic features of this extract led to an increased activity of gonadotropin releasing hormone secreting neurons [54]. On the other hand, WS root extract was found to decrease libido and sexual function which led to impotency and erectile dysfunction in animal studies [30]. Ethanolic WS fruit and stem extract were found to induce infertility in male rats due to the decrease in sperm motility, count, and degeneration of seminiferous tubules, although this extract did not have an effect on sperm morphology [28,53,56].
Prabu et al. in a study on male rats found that hydroalcoholic WS root extract was found to decrease white blood cell and lymphocyte counts in blood, but no considerable effect on reproductive indices [40]. Alcoholic WS root extract can decrease estrogen and cholesterol level in female Wistar mice and recover corpus luteum, graafian follicles, and germinal epithelium which has been damaged due to the chlorpyrifos exposure [35].
In a study investigating effects of 6.5 mg of WS root extract on Nile tilapia, it was found that this extract with androgenic effects decreased prolactin level and estrogen level by inhibiting aromatase activity and induced male phenotype formation; this phenomenon was proposed to be due to components such as tannin, saponins, terpenoids, steroids, and flavonoids [46].

Discussion
Traditional and complementary medicine have been more popular nowadays to cure health related conditions [67]. This proposes a new strong potential in traditional and complementary medicine to come up with new medical combinations with fewer side effects [68][69][70]. Traditional Persian medicine is one of the most well-known categories of traditional medicine using herbal medicine as one of the main therapeutic modalities [71].
Based on the present study, it was shown that extracts of WS fruits, leaves, stems, and especially roots enhance sperm quality indices such as motility and count in men [12,20,24,25] and also decrease the effects of chemical toxins on gonads in both men and women [13, 15, 29, 33-38, 41, 44, 45, 59]. WS can increase gonadal weight in both sexes, enhance folliculogenesis and spermatogenesis, and improve LH, FSH, and testosterone balances [15,27,31,35,36,38,42,44,45]. Sexual behavior indices such as female sexual function index and female sexual distress index improve statistically significant after WS extract administration [21].
The mechanism of WS effect on the reproductive system is not known entirely yet, but this mechanism is proposed to be linked to the antioxidative features and ability to improve the hormonal balance of LH, FSH, and testosterone and improve detoxification process. Also, the GABA mimetic feature of WS extract is thought to play the main role in inducing gonadotropin releasing hormone secretion and improving hormonal balance [23, 27, 31, 34-36, 42, 44, 47, 51]. In the male reproductive system, it is assumed that WS by providing metal ions facilitates enzyme activities, modifies oxidative stress, and prevents cell apoptosis [23]. The root extract of WS has been shown to induce alanine transaminase activity which increases alanine in seminal fluid leading to a less oxidative stress index and improved semen quality [24]. Normalizing lactate, phenylalanine, glutamine, citrate, and histidine in seminal fluid are another feature of WS extract which improves enzymatic processes in tricarboxylic acid cycle (TCA) and fatty acid metabolism [12,59]. On the other hand, some animal studies have suggested that WS extract may cause reversible spermicidal and infertilizing effect in male and delayed puberty in both sexes; this might be due to the dose, preparation method, adjuvant components, and duration of use designated in mentioned studies [28,30,49,53,56].

Conclusion
Based on the results, it deems that Withania somnifera has a positive effect in the treatment of infertility both in male and female. Although some studies proposed that WS extract might have infertilizing and spermicidal effect. Due to the growing interest in using herbal medicine especially those which possess the antioxidative and reproductive system supporting properties, further studies are needed to be designed with higher population and more-structured methodology so a more precise and decisive conclusion can be made.

Conflicts of Interest
The authors declare that they have no conflicts of interest.