Written by Alejandro Andión
Maca (Lepidium meyenii) belongs to the Brassicaceae family and grows in the central Andes of Peru above 4000 meters of altitude where it has been cultivated for more than 2000 years. His first descriptions appear in the chronicles of the conquest of Peru. Up to thirteen varieties ranging from white to black have been described, varieties have been studied, such as black and red which showed different properties. These differences in biological properties seem to depend on the differences of the crop soil, rather than on the morphotypes, however, contrasts the fact that all varieties are presented in the same soil.
The adaptation of this plant to such adverse places determines that its morphological characteristic includes a very small aerial part and a bulky reserve zone (hypocotyl) that is located inside the farmland. The interest in this plant has crossed our borders in such a way that an attempt has been made to grow it outside its natural habitat in Europe, without flattering results.
Its life cycle has two well-defined stages, the first called the vegetative one where the reservant root is produced, which is used as food by the population. The other stage known as the reproductive one consists of the production of botanical seed, both stages are completed in two consecutive years and, therefore, it is known as a biennial crop.
In the aqueous fraction of maca have been found free sugars, amino acids with a high component of proline, uridine, malic acid and a fraction containing glucosinolates, while in the non-polar phase there are macaenes and macamides (polyunsaturated fatty acids and their corresponding amides).
Maca is traditionally consumed as a mixture of different colors. Currently, maca is no longer only consumed in the areas of the central Andes, where it is produced, but there is a widespread use throughout the country.
Next, the benefits of this plant in different aspects of human health will be described and some studies that were carried out in this regard will be mentioned.
SEXUAL FUNCTION. 
Maca, particularly lipid extracts, improves sexual behavior in rodents, however, these results have not been able to be reproduced in subsequent studies.
Gelatinized maca (1.5 or 3.0 g/day) in normal males, improves sexual desire from 8 weeks of administration, long time for treatment on improvement of sexual desire. On the other hand, the use of maca extract improves sexual desire in male athletes at two weeks of treatment. A double-blind study using a dried maca extract (2.4 g/day) for twelve weeks showed a small but significant effect of maca on mild erectile dysfunction.
Two clinical trials suggest a favorable effect of maca on sexual dysfunction or sexual desire in healthy menopausal women or healthy adult males, respectively, while in another clinical trial reviewers state that there is no effect of maca on healthy cyclists. However, the results of the study show that maca extract significantly improves sexual desire compared to baseline (p=0.01), or placebo (p=0.03). A systematic review evaluating the effect of maca on improving sexual function in humans shows that the evidence is still limited.
In a clinical study without comparison with placebo, patients with sexual dysfunction induced by the use of serotonin reuptake inhibitors (SSRIs), who consumed 3.0 g/day of maca had an improvement in sexual function tests, which did not occur with the 1.5 g/day dose of maca; maca consumption being well tolerated.
The evaluation of the effect of maca consumption on sexual function still requires further studies with more appropriate and rigorous designs.
EXAMPLE OF A RECENT STUDY ON THE BENEFICIAL EFFECTS OF MACA ON SEXUAL FUNCTION. 
MALE FERTILITY. 
The aqueous extract obtained after the cooking of the maca hypocotyls and the hydroalcoholic extract, can increase the stages of mitosis of spermatogenesis in rats, after 14 days of treatment. Likewise, there is a dose-response effect that improves the stages of spermiation (VII-VIII) and mitosis in rats, after 7 days of treatment. After 42 days, black maca improved daily sperm production and increased sperm motility (p<0.05). No effect of red maca was observed while yellow maca had an intermediate effect.
Administration for 84 days of black or yellow maca increases sperm count in the epididymis; the three varieties (black, yellow and red) increase the sperm count in the vas deferens, without affecting the number of sperm in the testicles. These results would suggest an action of maca modulating sperm count.
In bulls, supplementation of the maca feed appears to improve the quantity, quality, and integrity of sperm DNA. Likewise, the mixture of black maca extracts with yacon leaves reverses the reduction of sperm and the increase in glucose induced by streptozotocin.
Administration of gelatinized maca to nine healthy males for 4 months shows at doses of 1.5 g or 3.0 g an increase in seminal volume, sperm count and motility. After 4 months of treatment, the number of motile sperm increased from 87.72 ± 19.87 million (mean ± standard error of the mean) to 183.16 ± 47.84 million (p<0.05).
Levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, estradiol and testosterone were not affected by maca treatment.
The lack of response of serum testosterone or the lack of activation of the androgen receptor by the action of maca suggests that the effects of maca on sperm quality or quantity are produced by another route other than testosterone and its receptor or FSH. In vitro studies indicate that both methanolic and aqueous extracts of maca show estrogenic activity in MCF-7 cell lines and having found no action on alpha estrogen receptors suggests an action on estrogen beta receptors, which has yet to be demonstrated.
EXAMPLE OF A RECENT STUDY ON THE BENEFICIAL EFFECTS OF MACA ON MALE FERTILITY. 
FEMALE FERTILITY. 
Maca does not affect the rate of implantation in mice, nor does it generate a greater number of eggs per cycle, nor does it affect the normal development of preimplantation embryos. However, the mice that received aqueous maca extract had a greater number of offspring than those in the control group. The same has been observed in guinea pigs treated with 90 g of maca/day for 100 days. In fish, maca has also been shown to promote the survival of fry and juveniles.
It has been reported that the use of phytoestrogens in the diet accelerates the time of vaginal opening in mice. Treatment with maca does not affect this variable, so the consumption of maca hypocotyls does not affect sexual maturation.
Studies in populations that traditionally consume maca indicate that this plant is consumed even during pregnancy.
However, it is necessary to carry out studies to determine its safety, even when it is consumed in early stages of gestation.
EXAMPLE OF A RECENT STUDY ON THE BENEFICIAL EFFECTS OF MACA ON FEMALE FERTILITY. 
MEMORY, ANXIETY AND DEPRESSION. 
A study of the effects of maca on cognitive function evaluated the action of three varieties of maca (red, black and yellow) on learning in ovariectomized mice using the “water search” test. That study determined that black maca has the best effect on spatial learning.
A second study determined that treatments with post-boiled aqueous and hydroalcoholic extracts of black maca reversed scopolamine-induced cognitive damage in male mice. Scopolamine is a muscarinic receptor antagonist that acutely mimics Alzheimer’s disease. In addition, both black maca extracts were shown to inhibit acetylcholinesterase activity, without modifying monoamine oxidase levels.
These results were confirmed using female mice where post-boiled aqueous and hydroalcoholic extracts of black maca were able to reverse the damage to memory and learning caused by ovariectomy.
The neuroprotective activity of maca has also been studied using experimental models in vitro and in vivo. In vitro, pretreatment with pentanus maca extract improves the viability of locust neurons, in the face of exposure to hydrogen peroxide (H2O2) in a concentration-dependent manner.
In rats it was observed that the pentanus extract presents a potential application as a neuroprotectant in rats with cerebral infarction due to occlusion of the middle cerebral artery. In humans, maca reduces depression and anxiety scores in apparently healthy adult males. Similarly, maca (3.5 g/d) for six weeks reduces psychological symptoms, including anxiety and depression, in postmenopausal women.
EXAMPLE OF A RECENT STUDY ON THE EFFECTS OF MACA ON MEMORY, ANXIETY AND DEPRESSION. 
Several studies evaluated the effectiveness of maca as an energy source drawing the following conclusions:
The soluble lipid extract of yellow maca (100 mg / kg) for three weeks, increased physical resistance, measured in terms of the time it reaches fatigue, by 41% of the control value, on the other hand, with the hydroalcoholic extract of black maca the increase in physical resistance is greater than 500%.
The administration of maca extract for 14 days significantly and faster improves the performance time in a cycling race of 40 km compared to baseline (p=0.01), but not compared to placebo (p>0.05).
In ten professional footballers, who for 60 days received three capsules of fresh maca concentrate, with 500 mg each per day, there is an average increase of 10.3% in oxygen consumption after administration.
While both human studies show a favorable effect of using maca for physical endurance, the increases are modest.
EXAMPLE OF A RECENT STUDY ON THE BENEFICIAL EFFECTS OF MACA AS AN ENERGIZER. 
The prostate, an accessory sex gland, contributes 30% of the total seminal fluid (60% are provided by the seminal vesicles and 10% by secretions from the epididymis and bulbo-urethral glands). The secretions of the prostate have the function of providing the fertilizing capacity to the sperm. Its growth and maintenance is mainly regulated by androgens, specifically by the conversion of testosterone to dihydrotestosterone (DHT), a reaction mediated by the enzyme 5-alpha-reductase.
From the age of 40, in almost half of men, a prostate growth known as benign prostatic hyperplasia (BPH) is observed that is characterized by signs and symptoms of the lower urinary tract that affects quality of life. Although alpha-1 adrenergic receptor blockers, 5 alpha reductase inhibitors such as finasteride, and the combination of therapies including tamsulosin-dutasteride, doxazosin-finasteride, terazosin-finasteride, tolterodine-tamsulosin, and rofecoxib-finasteride are part of the therapeutic strategy of choice for BPH, information on the use of phytotherapy for this disease has emerged in recent years. Among them, red maca is described.
One study evaluated the effect of a lyophilized aqueous extract of red maca on BPH induced by testosterone enanthate in adult rats of the Holtzman strain and red maca was able to reverse this effect on the prostate, following a dose-response pattern, without affecting the weight of the seminal vesicles. In this same study, a positive control group received finasteride reducing both the weight of the prostate and the seminal vesicles. These results suggest that maca does not act on 5 alpha reductase, but probably within the cell on transcription factors or perhaps on the estrogenic pathway.
Red maca reduces intraprostatic zinc levels (increased in BPH) when administered from day 1 to day 14 taking into account that testosterone enanthate is applied on day 1 and day 7.
It is currently important to conduct a clinical trial in patients suffering from BPH in order to determine its efficacy in humans.
EXAMPLE OF A RECENT STUDY ON THE BENEFICIAL EFFECTS OF MACA ON THE PROSTATE. 
During post menopause there is a drop in estrogen, which triggers a series of events that lead to osteoporosis. While hormone replacement therapy (HRT) has been shown to be effective in preventing bone loss and reducing the rate of fractures, the risk of serious side effects has led to a decrease in its use and preference for bisphosphonates such as alendronic acid or zoledronic acid. Phytotherapy has been suggested as an alternative to THR.
Red maca, having a protective effect on organs regulated by a balance of steroid hormones, where estrogenic activity plays an important role, suggests that this variety could have a significant effect on the homeostatic balance of other functions regulated by steroid hormones, such as bone metabolism.
In ovariectomized rats treated with ethanolic maca extracts at oral doses of 0.096 and 0.24 g extract/kg body weight for 28 weeks, high concentrations of ethanolic maca extract were found to prevent bone loss. Red maca like black maca, but not yellow maca, has an effect on osteoporosis similar to estradiol.
Unlike estradiol, none of the treatments with the three varieties of maca increased uterine weight, suggesting that maca has a specific action on that organ. Estradiol acts through two alpha and beta receptors. The estradiol alpha receptor may oppose the action of the beta receptor. It is known that the beta receptor of estradiol, although it is widely distributed in the body, is not mostly expressed in the uterus, so it is suggested that maca could activate beta estrogen receptors.
A study in the central Andes shows that maca consumers have lower fracture rates than those in the same area who do not consume maca, corroborating experimental results found in animals.
EXAMPLE OF A RECENT STUDY ON THE EFFECTS OF MACA AGAINST OSTEOPOROSIS. 
In a clinical study in normal males treated with gelatinized maca there was a reduction in diastolic blood pressure after 12 weeks of treatment.
Villagers who traditionally consume maca have lower systolic blood pressure than those who do not.
Maca also significantly inhibits angiotensin-converting enzyme I (ACE) in vitro. Maca contains high levels of potassium, an important nutrient for reducing the risk of hypertension.
More experimental and clinical studies are needed to demonstrate maca’s role in glucose metabolism, lipid metabolism and blood pressure regulation.
EXAMPLE OF A RECENT STUDY ON THE EFFECTS OF MACA ON METABOLISM. 
In a study conducted in residents at 4100 m altitude, it was found that in traditional maca consumers the health status score based on a validated questionnaire is maintained from 40 to 75 years, unlike the population that does not consume maca, who present a decrease in this score as age increases.
Interleukin 6, a compound that when increased in older people is associated with aging, is found in smaller quantities in Junín subjects residing at 4100 m altitude who consume maca, this is associated with better health status score and greater success in tests such as getting up and sitting five times from a chair without using the arms as support.
EXAMPLE OF A RECENT STUDY ON THE EFFECTS OF MACA AGAINST AGING. 
Aqueous and methanolic extracts of maca do not show hepatotoxicity in vitro. Likewise, the aqueous extract of maca in doses of 1 g of freeze-dried maca / kg in mice, does not alter the normal development of pre-implanted embryos. In rats, the different varieties of maca do not show acute toxicity at doses ≤ 17 g of dried maca hypocotyls/kg. Similarly, rats treated for 84 days with maca showed no adverse effects at doses of 1 g/kg body weight, and liver histology was similar to the control group.
In mice the LD50 is greater than 15 g maca/kg without histopathological alterations in the liver, pancreas, spleen, testicles or ovaries. However, in patients with metabolic syndrome, administration of maca at doses of 0.6 g/day for 90 days moderately increases the enzyme aspartate aminotransferase (AST) and diastolic blood pressure. This has not been confirmed in other studies that, rather, show that maca lowers both systolic and diastolic blood pressure. This may be due to the high potassium content or inhibitory activity of the angiotensin-converting enzyme described in vitro. Similarly, in experimental studies in hypercholesterolemic animals maca is not only non-toxic, but protects better against liver damage from hypercholesterolemia than atorvastatin.
The demonstration of the presence of alkaloids such as (1R,3S)-1-methyl tetrahydro-β-carboline-3-carboxylic acid in maca has caused concern in its consumption, particularly in the European market, for the suggestion of a toxic effect, so further studies are needed to evaluate the Bhutanolic fraction contained in this alkaloid and thus verify its efficacy and safety.
EXAMPLE OF A RECENT STUDY ON THE TOXICITY OF MACA. 
1. Gustavo F. Gonzales, Leonidas Villaorduña, Manuel Gasco, Julio Rubio, Carla Gonzales. (December, 2014). Maca (Lepidium meyenii Walp), una revisión sobre sus propiedades biológicas (Maca (Lepidium meyenii Walp), a review of its biological properties. http://www.scielo.org.pe/scielo.php?script=sci_arttext&pid=S1726-46342014000100015
2. Byung-Cheul Shin, Myeong Soo Lee, Eun Jin Yang, Hyun-Suk Lim, Edgard Ernst. (October, 2010). Maca (L.meyenii) for improving sexual function: a systematic review. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2928177/
3. Myeong Soo Lee, Hye Won Lee, Sooseong You, Ki-Tae Ha. (October, 2016). The use of maca (Lepidium meyenii) to improve semen quality: A systematic review. https://pubmed.ncbi.nlm.nih.gov/27621241/
4. Fumiaki Uchiyama, Tamaki Jikyo, Ryosuke Takeda, Misato Ogata. (February 3, 2014). Lepidium meyenii (Maca) enhances the serum levels of luteinising hormone in female rats. https://pubmed.ncbi.nlm.nih.gov/24333960/
5. Julio Rubio , Wang Qiong, Xinmin Liu, Zhen Jiang, Haixia Dang, Shi-Lin Chen, Gustavo F Gonzales. (February 14, 2011). Aqueous Extract of Black Maca (Lepidium meyenii) on Memory Impairment Induced by Ovariectomy in Mice. https://pubmed.ncbi.nlm.nih.gov/18955369/
6. Eun Hye Choi , Jung Il Kang , Jae Young Cho , Seung Ho Lee , Tae Seok Kim , Ik Hyun Yeo , Hyang Sook Chun. (2012). Supplementation of standardized lipid-soluble extract from maca (Lepidium meyenii) increases swimming endurance capacity in rats. https://www.infona.pl/resource/bwmeta1.element.elsevier-d9cdee5d-14d3-37e7-b454-589e4ca87820
7. Alankar Shrivastava, Vipin B Gupta. (January, 2012). Various treatment options for benign prostatic hyperplasia: A current update. https://pubmed.ncbi.nlm.nih.gov/22923974/
8. Carla gonzales , Isaías Cárdenas-Valencia , Johanna Leiva-Revilla , Cecilia Anza-Ramírez , Julio Rubio , Gustavo F. González. (June 16, 2010). Effects of different varieties of Maca (Lepidium meyenii) on bone structure in ovariectomized rats.
9. Lena Galvez Ranilla , Young-In Kwon, Emmanouil Apostolidis, Kalidas Shetty. (June 2010). Phenolic compounds, antioxidant activity and in vitro inhibitory potential against key enzymes relevant for hyperglycemia and hypertension of commonly used medicinal plants, herbs and spices in Latin America. https://pubmed.ncbi.nlm.nih.gov/20185303/
10. Gustavo F Gonzales, Manuel Gasco, Iván Lozada-Requena. (December, 2013). Role of maca (Lepidium meyenii) consumption on serum interleukin-6 levels and health status in populations living in the Peruvian Central Andes over 4000 m of altitude.
11. LiverTox. (April 10, 2019). Clinical and Research Information on Drug-Induced Liver Injury. https://www.ncbi.nlm.nih.gov/books/NBK548552/