Maca has been described to improve fertility since many centuries ago [3
]. However, scientific evidences in peer reviewed journals were available since 2000 [5
]. The studies demonstrated that Maca increases male sexual behavior [11
] and increases sperm production [8
In relation to female reproduction, there is only one study demonstrating that Maca did not increase implantation rate in mice [9
]. We have demonstrated in the present study that implantation rate was not increased in mice after oral administration of 1 g/Kg BW of a lyophilized aqueous extract of Maca. However, interestingly, female mice that received Maca delivered more pups than the control group. This suggests that Maca may have a protective effect on the number of resorptions, having a less occurrence of them between day 7 of pregnancy and the subsequent days of pregnancy in the Maca treated group. Supplementation of Maca in diets improved growth rates and survival of rainbow trout Oncorhynchus mykiss
(Walbaum) alevins and juveniles [15
]. Some possible mechanisms through which Maca may act include increased uterine receptivity, altered immune functions and effects on vascular system [16
]. It is known that functional lymphocytic progesterone binding sites are needed for the maintenance of normal pregnancy, and that progesterone-mediated immunosuppression is needed for the maintenance of normal gestation [17
Litter size was higher at birth and at postnatal day 4 in the groups treated with Maca than in the controls. This effect seems to be due to a reduction in embryo resorption, since number of implantation sites were similar in mice treated with Maca than in controls. This effect seems not to be due to any estrogenic activity of Maca, since exposure to estradiol-17 beta or the proestrogen methoxychlor reduced litter size [18
Sex ratio was not affected after treatment with Maca. In fish, the period of sex differentiation is the most sensitive to possible action of phytochemicals with steroid activity. However, there was no significant difference in sex ratios between the control and Maca treated group of rainbow trout. P-nonyphenol, an environmental toxicant with estrogenic properties did not affect the sex ratio of live pups [19
]. All of these suggest that main effects of Maca were not due to increased estrogenic activity.
Sexual maturation in the litters was evaluated by the vaginal opening day. The pups were divided in two groups (< 7 pups and ≥ 7 pups). Fraternity size has a positive linear effect on age at vaginal opening. Lower litter size was related to early age at vaginal opening day. This has been observed previously [20
]. This difference seems to be due to differences in dietary energy density [21
]. When comparing both sub-groups with their respective controls, we observed that Maca had not effect on the VO day. Dietary phytoestrogens has been shown to accelerate the time of vaginal opening in immature CD-1 mice [22
]. Since Maca does not affect the VO day, it is suggested that phytoestrogens present in Maca has little impact on reproductive parameters assessed in the present study.
Maca contains sterols, such as campesterols (27.3%), ergosterol (13.6%), brassicasterol (9.1%) Δ7,22
-ergostadienol (4.5%) and sitosterol (45.5 %) [23
], the latter having phytoestrogen activity. It has been suggested that β-sitosterol could cross the placenta [24
]. In humans, it has been demonstrated that sitosterol can be excreted in milk and therefore, enter the neonate [25
]. Maca chemical composition includes sitosterol, this compound would exert its effect on pups.
Treatment with Maca also increases male sexual behavior [12
] and sperm production in mice and rats [7
]. It is probable that main effects of Maca increasing uterine weight and litter size were not due to an estrogenic effect but to a progestin-like one, since Maca chemical composition include other sterols besides phytoestrogen sitosterol. Progesterone would certainly affect both, uterine weight via progesterone receptors, as well as prevent abortion. In mice and rats, progesterone is much more important in maintaining pregnancy than estrogen [16
]. Moreover, physiological level of progesterone acts in conjunction with androgens to facilitate copulatory behavior in male rats and mice [26
]. In addition, one of the most potent phytoestrogenic substance -6-(1,1-dimethylallyl) naringenin (6-DMAN)- did not have any effect on uterine wet weight in ovariectomized rats [28
]. Our study demonstrates that Maca increases uterine weight. It is suggested that this activity may be produced by a progestin-like effect. However, more studies need to be performed to clarify this proposed mechanism.