LE Magazine July 1998
It's been almost three years since the Life Extension Foundation presented findings about therapies to boost sex drive. Following that report, other media featured sensational stories on Foundation members who were using aphrodisiac products we had written about. This resulted in an avalanche of phone calls from the public whose only concern was to get their hands on these products as quickly as possible. So great was the response that it was difficult for Foundation members to reach us by phone during this period. In this first of two reports, we focus strictly on the scientific evidence about aphrodisiacs. Unlike our previous report, we are not including explicit, anecdotal testimonials about the sexual effects that were described by the study participants.
By William Faloon
Sexual enjoyment is of paramount importance to a great many people, increasingly so as we age. For a variety of biological reasons, our ability to function sexually declines as we grow older. Thus, it's no wonder that so-called aphrodisiac drugs or compounds have been popular for years.
Sex-enhancing supplements for men are widely sold throughout the world, more so in other countries than in the United States. But questions abound: Do these compounds really work? Are they equally effective for men and for women? Do they have any side effects that one should be concerned about?
One thing is for certain. The recent national fixation on the new potency pill Viagra only underscores how central the role of sexual intimacy is in our lives. Less noticed by the public, but equally important, is the increased scientific scrutiny of alternate and safer natural compounds that also demonstrate aphrodisiac properties.
Here, we'll take a hard look at plant-based compounds and prescription drugs that may have sex-boosting qualities, the science that has been conducted, and the varying biological mechanisms by which they work.
But first, a question: What common factors are there that may cause loss of libido?
Aging men often attribute their reduced sexual potency to testosterone deficiency, yet products that increase testosterone levels only produce a temporary sex boost for most people. Testosterone is the hormone responsible for sex drive in both men and women. For testosterone to promote youthful sexual interest, satisfaction, and performance, it must be freely available to brain cell receptor sites. However, as people age, testosterone becomes bound to serum globulin and is not available to the sex stimulating centers in the brain.
There is much confusion about the benefits and dangers of testosterone. About 90 percent of testosterone is produced by the testes, the remainder by the adrenal glands. Testosterone functions as an aphrodisiac hormone in brain cells, and as an anabolic hormone in the development of bone and skeletal muscle. But remember, testosterone that becomes bound to serum globulin is not available to cell receptor sites and fails to induce a libido effect. It is, therefore, desirable to increase levels of "free testosterone" in order to ignite sexual arousal in the brain.
The hormone that controls levels of free testosterone is sex hormone binding globulin (SHBG). When testosterone binds to SHBG, it loses its biological activity and becomes known as "bound testosterone," as opposed to the desirable free testosterone. One measure of SHBG's binding capacity shows that the average value in men under age 45 is 2.85, but increases to 4.66 and higher as men approach 60, indicating that more testosterone becomes bound to globulin through the actions of SHBG as we age.
A confirming study showed that the total testosterone levels of men aged 50 to 70 was not significantly different from younger adults, but that the younger adults had a much greater percentage of free (sex-arousing) testosterone. These studies showed that the decline in sexual interest with advancing age is not due to the amount of testosterone produced, but rather to the increased binding of testosterone to globulin by SHBG. This explains why most older men who are on testosterone-replacement therapy do not report a long-term aphrodisiac effects...that is, the artificially administered testosterone becomes bound by SHBG, and is not bioavailable to neuronal receptor sites where it would normally produce a libido-enhancing effect.
It should be noted that the liver also causes testosterone to bind to globulin. This liver-induced binding of testosterone is worsened by the use of sedatives, anti-hypertensives, tranquilizers and alcoholic beverages, and thus overuse of drugs and alcohol could explain why some men do not experience a libido-enhancing effect when consuming plant-based aphrodisiacs. An interesting published review, "How Desire Dies" (Nature, 381/6584, 1996), discusses how frequently prescribed drugs, such as beta-blockers and antidepressants, cause sexual dysfunction. Prescription drugs of all sorts have been linked to inhibition of libido.
Logically, one way of increasing libido in older men would be to block the testosterone-binding effects of SHBG. This would leave more testosterone in its free, sexually activating form.
Nettle Extract's Effects
A highly concentrated extract from the nettle root provides a unique mechanism for increasing levels of free testosterone. Recent European research has identified constituents of nettle root that bind to SHBG in place of testosterone, thus reducing SHBG's binding of free testosterone. As the authors of one study state, these constituents of nettle root "may influence the blood level of free, i.e. active, steroid hormones by displacing them from the SHBG binding site."
The prostate gland also benefits from nettle root. In Germany, nettle root has been used for decades as a treatment for benign prostatic hyperplasia (enlargement of the prostate gland). A metabolite of testosterone called DHT (dihydrotestosterone) stimulates prostate growth, leading to enlargement, as well as excess facial hair and hair loss at the top of the head. Nettle root inhibits the binding of DHT to attachment sites on the prostate membrane.
Enhancing Genital Sensitivity
While free testosterone stimulates sex cell receptor sites in the brain, there are aging-induced changes in the genital regions of men and women that must also be corrected if a youthful libido is to be maintained or restored.
Few doctors understand the biochemical mechanisms involved in sex organ stimulation. It is well known that free testosterone is required to activate sex cell receptor sites in the brain. For stimulation of sex cells in the genital area, however, a naturally produced chemical is needed to relax blood vessels in a part of the human anatomy called the corpus cavernosum.
The corpus cavernosum is a spongy bundle of tiny nerves, surrounded and filled with blood vessels, and located in the penis and clitoris that transmits endorphin-stimulating impulses to the brain: For men, penile erection and optimal sensation mandates proper function of the corpus cavernosum, and for women, the ability to enjoy sex and achieve orgasm is often dependent on clitoral corpus cavernosum activity.
The corpus cavernosum becomes active when it becomes engorged with blood during periods of sexual excitement, and its stimulation is dependent on the relaxation of genital muscles during sexual arousal. Nitric oxide and its metabolite cyclic GMP are the two dominant biochemicals that induce genital muscle relaxation, and subsequently increased blood flow to the sexually sensitive corpus cavernosum.
The Role of Arginine
The amino acid arginine promotes natural nitric oxide production in the body. By enhancing nitric oxide and subsequent cyclic GMP synthesis, arginine enlarges blood vessels in the corpus cavernosum that can lead to enhanced sensation and penile erection. Arginine is given to prize race horses at stud to improve the frequency of their sexual encounters, and to improve the quality of their sperm.
Like the new prescription potency drug Viagra (see sidebar story, opposite), arginine works to boost cyclic GMP levels. Arginine causes the production of nitric oxide that leads to increased levels of cyclic GMP. The longer that cyclic GMP levels are maintained, the better the chance of achieving and maintaining an erection. (One benefit of arginine supplementation is that it is much less costly than Viagra.)
But arginine is not just for men. The nitric oxide produced from arginine improves vaginal circulation in women and has been shown to stimulate the perivascular nerves in the genital area involved in sexual arousal. Arginine is recommended as a libido-enhancing supplement by scientists and doctors familiar with this amino acid's ability to stimulate nitric oxide synthesis.
The dose of arginine needed to enhance sexual function has been estimated to be between 6 and 12 grams a day. There are a variety of arginine supplements available. One practical approach would be to take three to four 1,000-mg capsules of arginine, three times a day. Others have reported that taking a large dose of arginine an hour before an anticipated sexual encounter produces a significant effect.
In addition to the use of nettle root and arginine, French scientists have identified a new herbal extract, Muira puama, that has shown significant libido-enhancing effects in two clinical studies. Muira puama, from a plant in the Amazon region of South America, is widely used as an aphrodisiac, tonic and cure for rheumatism and muscle paralysis.
Muira puama has been the subject of two published clinical studies conducted by Dr. Jacques Waynberg, an eminent medical sexologist and author of 10 books on the subject. The first study, conducted at the Institute of Sexology in Paris under Waynberg's supervision, was reported in the November 1994 issue of The American Journal of Natural Medicine. The study population consisted of 262 men complaining of lack of sexual desire, or inability to attain or maintain erection.
The result: After two weeks, 62 percent of patients with loss of libido rated the treatment as having a dynamic effect, while 52 percent of patients with erectile dysfunction rated the treatment as beneficial.
Waynberg's second study, "Male Sexual Asthenia," focused on sexual difficulties associated with asthenia, a deficiency state characterized by fatigue, loss of strength or debility. The study population consisted of 100 men over 18 years of age who complained of impotence or loss of libido, or both. A total of 94 men completed the study. Muira puama treatment led to significantly increased frequency of intercourse for 66 percent of couples. Of the 46 men who complained of loss of desire, 70 percent reported intensification of libido. The stability of erection during intercourse was restored in 55 percent of patients, and 66 percent of men reported a reduction in fatigue. Other beneficial effects included improvement in sleep and morning erections.
Treatment with Muira puama was much more effective in cases with the least psychosomatic involvement. Of the 26 men diagnosed with common sexual asthenia without noticeable sign of psychosomatic disorder, the treatment was effective for asthenia in 100 percent of cases, for lack of libido in 85 percent of cases, and for inability to obtain an erection in 90 percent of cases."Few in number are the plants that seem to have a reliable reputation as true aphrodisiacs. Snake oil remedies abound, and confusion, dishonesty and hyped-up placebo razzmatazz carry the day. Out of this mess, one plant appears to have risen above the competition. The plant is called Muira puama."
-Daniel Mowrey, Ph.D.
Herbal Tonic Therapies
The latter finding confirms the broad tonic action of Muira puama on conditions of fatigue and stress-related sexual dysfunction. Since Muira puama is not an artificial stimulant, it fortifies the system over a period of time. Some men report increased vitality within two weeks, while the full effects build over several weeks.
Waynberg notes that his toxicology studies and observations corroborate the conclusions of the scientific literature on the absence of toxicity of Muira puama, which is well tolerated by men in generally good health.
An early French study found Muira puama to be effective in gastrointestinal and circulatory asthenia, as well as impotence. Three of the most respected scientific authorities on medical herbalism recommend Muira puama. In recently published books, James Duke, Ph.D., chief of the United States Department of Agriculture's Medical Plant Laboratory, and Michael Murray, N.D., recommend Muira puama for erectile dysfunction or lack of libido. In addition, Daniel Mowrey, Ph.D., states the following in his book Herbal Tonic Therapies:
"Few in number are the plants that seem to have a reliable reputation as true aphrodisiacs.... Snake oil remedies abound, and confusion, dishonesty, and hyped-up placebo razzmatazz carry the day. Out of this mess, one plant, virtually unknown to most Americans, appears to have risen above the competition. The plant is called Muira puama. And though not much is known scientifically about the plant, all indications would lead one to believe that here is a material with the potential for making an important and significant contribution to the health of the male reproductive system."
Complementing all of the above, adequate zinc levels are essential for hormonal activity and reproductive health, as well as for normal, physiological function in both men and women.
In adult males, the testes and prostate have particularly high concentrations of zinc. The sites where male hormones attach to cells (androgen receptors) require zinc in order to function.
Zinc deficiency substantially reduces testosterone levels, sperm production and muscle endurance. Research suggests that zinc deficiency also may reduce the life span of ejaculated sperm.
A recent study examined marginal zinc deficiency in young men, 27 to 28 years of age, and older men from 55 to 73. When young men were put on diets in which zinc intake was restricted, their serum testosterone levels declined by an average of 73.4 percent after 20 weeks. In contrast, when older men with marginal zinc deficiency were given oral zinc supplementation for three to six months, their serum testosterone levels increased by an average of 92.8 percent. In fact, the elderly men taking a zinc supplement had serum testosterone levels 50.9 percent higher than the young men whose dietary zinc was restricted.
Another study demonstrated that only five weeks of dietary zinc restriction in young men significantly reduced serum testosterone levels, as well as the amount of ejaculated semen.
While zinc deficiency is prevalent throughout the world, clinical evaluation of mild deficiency is uncertain. A 1994 study noted, "Suspicions that mild zinc deficiency is common among the elderly cannot be confirmed or refuted because definitive indicators of zinc status are lacking."
The authors point out, "Decreased testosterone levels, problems with wound healing, and age-associated energy [deficient energy or immune function] may all be related to marginal zinc status in the elderly." They also note that serum zinc levels decrease with age, and that the ability to absorb zinc is also decreased with age. However, "The detection of mild zinc deficiency remains difficult and impractical," they note. Conventional indicators such as serum zinc levels and alkaline phosphatase levels do not respond in a consistent way to changes in zinc intake. The authors studied the enzyme 5'-nucleotidase, which they propose as a potentially more reliable indicator of zinc status.
Much of our detailed understanding of the hormonal mechanisms involved in zinc deficiency derives from studies conducted on rats. One study found that the testicular cells of zinc-deficient rats lost their ability to convert lipids into sex hormones. Other rat studies have found that zinc deficiency significantly reduces the concentration of androgen receptors sites in reproductive organs and the liver.
The authors note that the effects of zinc deficiency on liver metabolism and binding of sex hormones acts in a similar way to the effects on the body of alcohol or castration. They conclude that such zinc deficiency "plays a pathogenic role in feminization and reproductive dysfunction."
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