Nutrients and Botanicals for Erectile Dysfunction: Examining the Evidence

Alternative Medicine Review,  March, 2004  by Douglas MacKay

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Abstract

Erectile dysfunction effects 50 percent of men ages 40-70 in the United States and is considered an important public health problem by the National Institutes of Health. Consumers are exposed to a plethora of natural products claiming to restore erection and sexual vitality. A review of the available empirical evidence reveals most naturally occurring compounds lack adequate clinical trials to support efficacy. However, arginine, yohimbine, Panax ginseng, maca, and Ginkgo biloba all have some degree of evidence they may be helpful for erectile dysfunction. Improvements in penile endothelial L-arginine-nitric oxide activity appear to be a unifying explanation for the actions of these naturally occurring agents. (Altern Med Rev 2004;9(1):4-16)

Introduction

Throughout history the erect penis has been a symbol of power and virility. (1) In men the inability to achieve or maintain an erection sufficient for satisfactory sexual function, known as erectile dysfunction (ED), (2) can have a considerable impact on interpersonal relationships and quality of life. The prevalence, cost, and psychosocial impact of ED has been described as an important public health problem by a National Institutes of Health Consensus Panel. (2) Results of a community-based, randomized, observational survey of men conducted from 1987-1989 in cities and towns near Boston, Massachusetts, found 52 percent of men ages 40-70 had some degree of ED. Incidence of complete ED tripled--from 5 to 15 percent--between age 40 and 70, while the incidence of moderate ED doubled from 17 to 34 percent during this same age span. In addition, 60 percent of men were estimated not to be impotent at age 40, with a decrease to 33 percent by age 70 (Figure 1). (3) From this data, an estimated 30 million men in the United States are affected by some degree of ED. (4) Researchers speculate that as baby boomers grow older and the global population ages, the prevalence of ED will more than double in the next 25 years, possibly affecting more than 330 million men worldwide. (5) The annual cost of ED in the United States, as estimated from the number of physician-related visits in 1985, was $146,000,000. (3)

[FIGURE 1 OMITTED]

Internationally, most men with ED fail to pursue treatment due to the complex nature of sexuality, taboos, cultural restrictions, and acceptance of ED as a normal sequela of aging. Worldwide, an estimated 10 percent of patients with ED seek medical attention. (6) Availability of oral sildenafil (Viagra,) in 1998 as the first efficacious oral treatment for ED of various causes has resulted in increased awareness and number of patients seeking treatment. Sildenafil has proven itself a valuable tool in the management of ED, but is not without limitations. While it provides symptomatic relief, it is not a cure, it is costly, and the long-term risks and benefits are unproven. (7) The success of sildenafil has led investigators on a feverish pursuit of other agents that can ultimately compete with this synthetic "love drug." (8) Scientists are beginning to gather empirical data on naturally occurring compounds that have been used historically as agents to increase male sexual function.

Currently, the efficacy of most natural agents remains moderate-to-uncertain. Many natural agents used to treat ED are attractive because they provide health benefits beyond those related to ED and are inexpensive compared to prescription medications. This article explores the empirical evidence related to the efficacy of various orally available natural agents used to treat ED.

Physiology of Normal Erection

Leonardo Da Vinci, through his dissection of cadaverous penises, was the first scientist to realize that during an erection the penis fills with blood. During his investigation, Da Vinci wrote, "The penis does not obey the order of its master, who tries to erect or shrink it at will, whereas instead the penis erects freely while its master is asleep. The penis must be said to have its own mind, by any stretch of the imagination." (5) Since Da Vinci's observations 500 years ago, investigators have determined the penis does not have a mind of its own, but is largely under the control of the central nervous system.

An erection requires intact psychological, neural, and vascular responses and reflects a dynamic balance of excitatory and inhibitory forces. Sexual stimulation causes excitatory signals to originate in the brain, resulting in the terminals of the axons of the parasympathetic nerves releasing nitric oxide (NO) gas directly and indirectly via endothelial cells in the penis (Figure 2). Simultaneously, the outflow from the sympathetic nerves is inactivated. NO gas diffuses into smooth muscle cells lining the arteries of the corpus cavernosum (spongy erectile tissue) acting as a chemical messenger, which activates guanylate cyclase (GC) within the muscle. Subsequently, GC converts the nucleotide guanosine triphosphate (GTP) into cyclic guanosine monophosphate (cGMP), which raises the intracellular concentration of cGMP. Guanosine monophosphate in turn causes smooth muscles of the penile arteries to relax, causing more blood to flow into the organ. The spongy erectile tissue of the penis becomes engorged with blood, causing compression of the veins that normally drain blood from the penis. Pressure created by the additional blood squeezes the veins until they are nearly closed, trapping blood within the corpus cavernosum and producing an erection. The erection eventually subsides because cGMP is hydrolyzed by phosphodiesterase type 5 enzymes (PDE5) to inactive GMP.