Maca (Lepidum meyenii, Brassicaceae), a root vegetable grown in the Andean region of Peru, is widely used for its nutritional and therapeutic properties. Maca is said to improve male and female reproductive activity in diverse ways, from increasing arousal and reducing symptoms of menopause to boosting sperm quality, quantity, and sexual performance. Benefits to memory, depression, and anxiety, and prevention of osteoporosis have also been reported. The authors review research on maca's effects in male reproduction, performing a literature search for relevant reports from 2000 to 2019. Search results are not further discussed.
Thirteen maca phenotypes are known by the color of the edible tuber; best studied are the black, red, and yellow varieties. Tubers are used both fresh and dried in Peru. Fresh tubers are boiled in water to obtain a juice or dried in a traditional open-air process for two months. After drying, tubers are washed and ground into a flour with a particle size of 0.8 mm for storage and use in foods.
Dried tubers contain secondary metabolites formed during drying, such as macaridine, macamides, maca alkaloids, and glucosinolates, which are reportedly responsible for maca's bioactivity. Aqueous extracts have only shown efficacy when the tubers were crushed and boiled, again demonstrating the production of secondary metabolites during processing. A dose-response in vivo study found a maca extract safe in doses < 5.0 g/kg body weight/d, with greater effect on reproductive parameters at doses of 1.0 g/kg/d.
Almost all of reports cited in this review are in vitro or in vivo studies. Among the latter are studies in male mice, rats, horses, sheep, and cattle. Different effects are reported for different phenotypes and extracts. Black, yellow, and red maca had beneficial effects on spermatogenesis, increasing sperm numbers, quality, and motility. Maca boosted weights of testes and epididymis. Maca improved libido and sexual performance in animals with erectile dysfunction, attributed to alkaloids macaine 1, 2, 3, and 4. Black maca boosted daily sperm production and epididymal sperm motility; in one study, this effect appeared as soon as one day after beginning supplementation. In a rat study, yellow and black maca improved epididymal sperm counts and all three phenotypes increased sperm count in the vas deferens without altering daily sperm production.
Most improved spermatogenesis was seen with an ethyl acetate fraction of a black maca extract. Red maca prevented prostatic hyperplasia and reduced ventral prostate size in rats and mice. This occurred without altered serum testosterone or estrogen levels, suggesting an androgen-based effect that may be due to benzyl glucosinolate content. Yellow maca was reported to prevent high altitude-induced and other types of spermatogenic disruption. A study comparing yellow maca aqueous extract from tubers of different sizes, under different pH conditions, and via two routes of administration found extracts from larger tubers and reduced pH produced higher sperm counts. Oral administration was superior to intraperitoneal, perhaps because its passage through the gastrointestinal tract produced other bioactive molecules. Semen from stallions supplemented with yellow maca powder had improved resistance to disruption from cooling and storage.
Few human trials have followed these reports. Sexual dysfunction is a serious public health problem, negatively affecting relationships and psychological health. Drugs used to treat male sexual dysfunction carry risks of adverse events. Since maca has been used for generations in Peru, and is sold worldwide in powders, capsules, pills, flour, liquor, and extracts, the paucity of human studies is puzzling, according to the authors.
In normal men who took an aqueous ethanolic extract of maca for four months, neither serum testosterone nor estradiol levels were affected. Two double-blind, placebo-controlled, randomized clinical trials reported benefits in sexual health, mood, and perceived well-being. In another study, spray-dried extracts of red or black maca taken for 12 weeks boosted mood, energy, and health status, with red maca showing stronger effects. In addition to pharmacological studies, more clinical research, especially to investigate maca's spermatogenetic effects as seen in various mammals, is needed.
Tafuri S, Cocchia N, Vassetti A, et al. Lepidium meyenii
(maca) in male reproduction. [published online December 5, 2019]. Nat Prod Res
. doi: 10.1080/14786419.2019.1698572.