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Effect of Lepidium meyenii (MACA) on sexual desire and its absent relationship with serum testosterone levels in adult healthy men
G. F. Gonzales, A. Córdova, K. Vega, A. Chung, A. Villena, C. Góñez and S. Castillo
Instituto de Investigaciones de la Altura, and Department of Biological and Physiological Sciences (Faculty of Sciences and Philosophy), Universidad Peruana Cayetano Heredia, Lima, Peru
Key words. Lepidium meyenii—men Maca—serum testosterone—sexual desire
Correspondence: Gustavo F. Gonzales, Instituto de Investigaciones de la Altura, Universidad Peruana Cayetano Heredia, Postal Ofï¬ce 1843, Lima, Peru.
Fax 00 511 4821195; e-mail: iiad@upch.edu.pe
Summary
This study was a 12-week double blind placebo-controlled, randomized, parallel trial in which active treatment with different doses of Gelatinized Maca was compared with placebo. The study aimed to demonstrate if effect of Maca on subjective report of sexual desire was because of effect on mood or serum testosterone levels. Men aged 21–56 years received Maca in one of two doses: 1500 mg or 3000 mg or placebo. Self-perception on sexual desire, score for Hamilton test for depression, and Hamilton test for anxiety were measured at 4, 8 and 12 weeks of treatment. An improvement in sexual desire was observed with Maca since 8 weeks of treatment. Serum testosterone and estradiol levels were not different in men treated with Maca and in those treated with placebo (P:NS). Logistic regression analysis showed that Maca has an independent effect on sexual desire at 8 and 12 weeks of treatment, and this effect is not because of changes in either Hamilton scores for depression or anxiety or serum testosterone and estradiol levels. In conclusion, treatment with Maca improved sexual desire
Introduction
Sexual function is an important component of human quality of life and subjective well being. Sexual problems are widespread and adversely affect mood, well being, and interpersonal funcÂtioning (Laumann et al., 1999). Main sexual problems are related to sexual desire and male erectile dysfunction. Erectile dysfunction is probably the most commonly recognized and treated sexual dysfunction. It affects more than 30% of men aged 40–70 years (Feldman et al., 1994).
Successful treatment of sexual dysfunction may not only improve sexual relationships, but also overall quality of life. Alternatives for treatment of hypoactive sexual desire are scarcer. Testosterone is used because of its property to stimulate sexual desire in hypogonadal men (Matsumoto, 1994; Arver et al., 1996). Other compounds are potent regulators of sexual behaviour in animals but not in healthy men (Perras et al., 2001).
Despite the broad use of oral agents for erectile dysfunction (Boolell et al., 1996), and the use of testosterone for hypoactive sexual desire (Seidman, 2000), many people in the world prefer the use of natural plants. Traditional herbs have been a revolutionary breakthrough in the management of erectile dysfunction and have become known worldÂwide as treatment (Adimoelja, 2000). One example is the broad use of ginseng because of its supposed property to provoke sexuality (Kim et al., 1976).
More recently, aphrodisiac activity has been described for the root of Lepidium meyenii (Maca), a Peruvian plant (Zheng et al., 2000; Cicero et al., 2001). Additionally, a favourable effect on spermatogenesis has been observed in adult male rats (Gonzales et al., 2001a) and in adult men (Gonzales et al., 2001b). Maca (L. meyenii) is a Peruvian hypocotyl which belongs to the Brassicaceae family and grows exclusively between 4000m and 4500m altitude at the central Peruvian Andes. For centuries, it has been recognized traditionally for its properties to improve sexuality and fertility (see Obregon, 1998). Activity of the plant is located in the root. Actually, Maca is a commercially available product expended as a nutrient in different forms including as tablets in the drugstore. Despite the spread use in Peru no scienti ï¬ c evidence exists that Maca improves sexual desire in men.
The present study aimed to assess a role of Maca for sexual desire and to determine if this effect is because of changes in mood or in serum testosterÂone and estradiol levels in adult healthy men.
Patients and Methods
Design The study was a 12-week double-blind placebo-controlled, randomized, parallel trial in which two doses of Gelatinized Maca were orally administered and compared with the placebo.
The Institutional Review Board of the Scientific Research Of ï¬ ce from the Universidad Peruana Cayetano Heredia approved the study.
Subjects
Fifty-seven subjects (21–56 years) were included in the study. All subjects were in apparently good health. Men were randomly placed in one of three groups.
Two groups received active treatment whereas the other group received placebo. For 12 weeks, one group (n=30) received three tablets of 500 mg each of Gelatinized Maca (Maca Gelatinizada La Molina, Lima) per day (Maca 1.5 g ). The second group (n=15) received six daily tablets of Gelatinized Maca (3000 mg) and it was defined as Maca 3.0 g . The third group received tablets of placebo daily for the 12-week span in the same schedule as the Maca group. During the study, all men maintained their usual eating regimen.
Most of the subjects did not smoke or use drugs for at least 3 months before study, nor did they use dietary supplements.
Laboratorios Hersil ( Lima , Peru ) provided the tablets of Gelatinized Maca (Maca Gelatinizada La Molina). Each tablet contained 500 mg of dehydrated root of Maca (L. meyenii).
Venous blood samples were drawn after a 12-h overnight fasting at 4, 8 and 12 weeks of treatment. Blood was centrifuged at 1000 g , and serum was collected after centrifugation and kept frozen until assayed for hormone measurements.
Sexual Desire
Sexual desire was assessed using a subjective (self  report) response about the effect of treatment on sexual desire at 4, 8 and 12 weeks of treatment. The basal value (before treatment) was considered as 1. Each subject was asked if treatment diminished (score=0), did not change (score=1), increased mildly (score=3), or increased moderately to highly sexual desire (score=5).
Depression and Anxiety Tests
Mood was assessed using the Hamilton Depression Rating Scale (Mykletun et al., 2001), which has 17 questions. Anxiety was scored with the Hamilton Anxiety Rating Scale (Lobo et al., 2002) which assesses somatic and cognitive-affective aspects.
Hormone Measurement
Serum testosterone and estradiol were determined by radioimmunoassay (RIA) using an I 125 -testoster-one and I 125 -oestradiol, respectively, as radioactive marker. The assays have been performed using commercial kits (Diagnostic Products Co., Los Angeles , CA ). All samples were run in a same assay period. The within assay variation was 6.42% for estradiol, and 5.5% for testosterone. Sensitivity of testosterone assay was 4.0 pg ml 1 and that for estradiol assay was 8.0 pg ml 1 .
Statistical Analysis
Data were analysed using the statistical package Stata (version 7.0) for personal computer (Stata Corporation, College Station , TX , USA ). Data are presented as frequencies. Data of serum hormones were transformed to percentage. Data were also analysed comparing Maca-treated groups with respect to placebo group. The differences between frequencies before and during treatment were assessed by the chisquared test. Logistic regression analysis was performed to assess the independent effect of Maca on sexual desire after controlling for scores of Hamilton Depression and Hamilton Anxiety test. For this analysis, sexual desire was the dependent variable, and it was dichotomized as follows: Values 0 and 1 were recoded as 0 (no effect), and values 2 and 3 were recoded as 1 (improvement in sexual desire). A P < 0.05 was considered statistically significant.
Results After 4 weeks of treatment, two men of the placebo group reported that treatment increased sexual desire (16.6%), whereas at 8 and 12 weeks of treatment none of men from this group had increased sexual desire (0.0%). In the Maca treated group, at 4 weeks, 24.4% of men manifested that treatment increased sexual desire, whereas at 8 and 12 weeks of treatment, the prevalence of men manifesting increase of sexual desire was 40.0% and 42.2% respectively.
Table 1 shows the scores for sexual desire measured as a subjective self report for the question if treatment had an effect on sexual desire. The group treated with placebo did not change the score for sexual desire (P:NS), whereas the overall group treated with Maca increased significantly the score for sexual desire at 4, 8 and 12 weeks of treatment (P < 0.01). However, when data in the Maca group were compared with placebo, the differences were observed at 8 and 12 weeks.
Multivariate analyses are shown in Tables 2–4. Table 2 shows data observed at 4 weeks of treatment. Treatment is assessed as dummy variable comparing the effect of Maca in relation to placebo. Logistic regression analysis showed that Maca had no effect on sexual desire. Scores of depression and anxiety tests and serum testosterone and estradiol levels were not related to sexual desire in men. Tables 3 and 4 show data observed at 8 and 12 weeks of treatment with Maca (1.5 or 3.0 g ) or placebo. Treatment with Maca 1.5 g and Maca 3.0 g are independent variables associated to sexual desire at 8 and 12 weeks of treatment. No independent effect on sexual desire was observed with score of neither depression and anxiety tests nor serum testosterone and estradiol levels.
Discussion
During the last decade an increase in the use of plants in metropolitan areas of developed countries has been observed. A recent study in a metropolitan area of Minnesota demonstrates that herbs are used frequently to promote general health/well-being (Harnack et al., 2001). Sexual dif ï¬ culties are extremely prevalent among both men and women (Leiblum, 1999). Plants are extensively used to relieve sexual dysfunction, as it happens with ginseng, an essential constituent in traditional Chinese medicine. At least six million Americans use the root of this slow-growing perennial (Nocerino et al., 2000).
Table 1.
Effect of different doses of Maca or placebo on self-report about effect of treatment on sexual desire in apparently healthy men
Treatment |
0 weeks |
4 weeks |
8 weeks |
12 weeks |
Placebo |
1.00 |
1.33 ± 0.37 |
0.83 ± 0.11 |
0.83 ± 0.11 |
Maca |
1.00 |
1.84 ± 0.24*,a |
2.47 ± 0.27*,b |
2.47 ± 0.27*,b |
Data are mean ± standard error of mean (SEM). a P:NS; b P < 0.001 with respect to placebo. *P < 0.01 with respect to basal values (0 weeks).
Table 2.
Logistic regression analysis for the probability that Maca, anxiety Hamilton score, depression Hamilton score, serum testosterone and estradiol levels affect self perception of improvement in sexual desire after 4 weeks of treatment
Variable |
Coefficient of regression |
Standard error |
P >|z| |
(95% CI) |
Maca 1.5 g |
1.10 |
0.95 |
NS |
-0.77 2.97 |
Maca 3.0 g |
-0.06 |
1.12 |
NS |
-2.25 2.12 |
Anxiety score |
0.08 |
0.10 |
NS |
-0.13 0.28 |
Depression score |
-0.11 |
0.13 |
NS |
-0.35 0.14 |
Serum testosterone |
0.24 |
0.19 |
NS |
-0.13 0.61 |
Serum estradiol |
-0.03 |
0.03 |
NS |
-0.09 0.04 |
Constant |
-2.31 |
1.63 |
NS |
-5.51 0.89 |
CI, confidence interval. Maca (1.5 or 3.0 g ) were analysed as variable dummy with respect to placebo. |
|
|
||
Logistic Regression v 2(6) = 4.58; P > v 2= 0.5984; Pseudo r 2 = 0.0755. |
|
|
||
Table 3.
Logistic regression analysis for the probability that Maca, anxiety Hamilton score, depression Hamilton score, serum testosterone and estradiol levels affect self perception of improvement in sexual desire after 8 weeks of treatment
Variable |
Coefficient of regression |
Standard error |
P >|z| |
(95% CI) |
Maca 1.5 g |
19.60 |
0.85 |
0.0001 |
17.93 21.27 |
Maca 3.0 g |
18.54 |
1.46 |
0.0001 |
15.16 21.27 |
Anxiety score |
-0.14 |
0.14 |
NS |
-.040 0.13 |
Depression score |
0.19 |
0.16 |
NS |
-0.13 0.51 |
Serum testosterone |
0.16 |
0.19 |
NS |
-0.22 0.54 |
Serum oestradiol |
0.02 |
0.03 |
NS |
-0.04 0.07 |
Constant |
-21.15 |
1.51 |
0.0001 |
-24.12 -18.18 |
Maca (1.5 or 3.0 g ) were analysed as variable dummy with respect to placebo. Logistic Regression v 2 (6)=13.25; P > v = 0.0393; Pseudo r = 0.2382.
Table 4.
Logistic regression analysis for the probability that Maca, anxiety Hamilton score, depression Hamilton score, serum testosterone and estradiol levels affect self perception of improvement in sexual desire after 12 weeks of treatment
Variable |
Coefficient of regression |
Standard error |
P >|z| |
(95% CI) |
Maca 1.5 g |
21.37 |
1.01 |
0.0001 |
19.20 23.16 |
Maca 3.0 g |
19.85 |
1.06 |
0.0001 |
17.78 21.92 |
Anxiety score |
-0.03 |
0.17 |
NS |
-0.35 -0.30 |
Depression score |
0.22 |
0.15 |
NS |
-0.08 0.52 |
Serum testosterone |
-0.49 |
0.35 |
NS |
-1.17 0.19 |
Serum oestradiol |
0.02 |
0.03 |
NS |
-0.04 0.08 |
Constant |
-19.70 |
1.83 |
0.0001 |
-23.29 -16.12 |
Maca (1.5 or 3.0 g ) were analysed as variable dummy with respect to placebo. Logistic Regression v (6) = 16.12; P > v 2 = 0.0131; Pseudo r = 0.2898.
The results of the present study demonstrate that another root, Maca (L. meyenii) which grows in the central Andes of Peru in altitudes between 4000 and 4500 m may also improve sexual desire. In fact, Maca (1.5 or 3.0 g day) administered orally in tablets during 12 weeks has a beneficial effect on subjective sexual desire in adult healthy men. These data confirm results obtained in mice and rats (Zheng et al., 2000; Cicero et al., 2001). Our results demonstrate that effect of Maca in healthy men is noticeable since 60 days of treatment. Certainly, data at 30 days of treatment did not show differÂences between Maca treated men and placebo treated men. We have not demonstrated a higher effect with 3.0 g compared to 1.5 g of Maca. We have not a clear explanation for this. Further studies will be necessary to clarify a dose-response effect.
Sexual desire may be affected by behavioural depression, stress (Kumar et al., 2001), anxiety (Rowland et al., 1987) and sedation (Ratnasooriya & Dharmasiri, 2000). Improvement of depression by selective serotonin reuptake inhibitors in depressed patients has been associated with improvement in sexual functioning (Ekselitus & von Knorring, 2001; Michelson et al., 2001). In this case, improvement in sexual desire was related to reversion of depression rather than an effect of the increased serotonergic activity, as serotonin stimulation inhibits sexual function (Gonzales et al., 1982).
Maca is prescribed because of its supposed properties to decrease anxiety, depression, and stress. However, the present study has demonstrated that the effect of Maca on sexual desire is independent of an effect on anxiety and/or depression. Furthermore, improvement in sexual desire by Maca was not related to any increase in serum testosterone or estradiol levels. In fact, multivariÂate analysis has demonstrated an effect of Maca on sexual desire but this effect is independent of changes in scores for depression test, scores for anxiety text, serum testosterone levels, and serum estradiol levels.
Effect of Maca on sexual desire could be because of any unknown chemical signal, i.e., phytoestrogens. Increase in serum testosterone levels in men with low desire by low serum testosterone levels resulted in resumption of sexual activity (Jannini et al., 1999). This is not the situation of our study as men were apparently healthy. Brown et al., (1978) provided evidence that differences among men in circulating testosterone concentration within the normal range do not account for differences in sexual activity and interest. Ansong & Punwaney (1999) have studied the relationship between sexual drive and serum testosterone levels among men with erectile dysÂfunction. Men were classified according to low (50.9%), moderate (35.2%), and high (13.9%) sexual drive. Serum testosterone levels were not different among these groups.
Data from our study demonstrate that serum testosterone levels were not associated to the improvement in sexual desire by treatment with Maca. According to our data and from others, testosterone is necessary, although not sufficient for normal or increased levels of sexual desire. In addition, supra-physiological levels of testosterone maintained for up to 2 months can promote some aspects of sexual reusability without stimulating sexual activity in normal men (Anderson et al., 1992). These suggest that physiological levels of plasma testosterone do not provide a maximal stimulus in terms of sexual reusability. Moreover, an increase in plasma testosterone into supra-physiological range is not associated with any detectable changes in sexual behaviour (Anderson et al., 1992). Therefore, all of these data suggest that testosterone should not be used when sexual desire is attempted to improve in men with normal serum testosterone levels. Treatment with Maca may be an interesting alternative, as it improves sexual desire without affecting serum testosterone levels.
As other plants, Maca may contain phytoestrogens. Phytoestrogens may have estrogenic or anti-estrogenic activities (Kuiper et al., 1998). A possible role of estrogens on both human male fertility and sexuality has also been suggested by recent studies (Rochira et al., 2001). Male rodents show impaired sexual behaviour and fertility as a consequence of oestrogen defect (O'Donnell et al., 2001). Therefore, it is an interesting suggestion that estrogenic substances should be considered also as male hormones (O'Donnell et al., 2001).
In conclusion, treatment with tablets of Maca at 1.5–3.0 g day for 8 or 12 weeks improved sexual desire in healthy men independently of changes in mood or serum testosterone and estradiol levels.
Acknowledgements
The authors thank Manuel Gasco and Julio Rubio for their help in field work. The Hersil Laboratories and the Universidad Peruana Cayetano Heredia supported this study.
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