From The September 2000 Issue of Nutrition Science News
by Lise N. Alschuler, N.D.
Could the fruit of a plant many consider a weed ease the symptoms of a painful condition that affects so many older men? Native Americans have used saw palmetto (Serenoa repens, S. serrulata and Sabal serrulatum) berries for hundreds of years as a nutritive tonic and a reproductive strengthener. They also used the herb to flush kidney stones, increase male fertility and treat breast disorders, urinary tract irritations and weakened urine flow. While many of these historical applications have yet to be studied, saw palmetto is touted today for its ability to reduce symptoms of benign prostatic hyperplasia (BPH).
BPH, characterized by a slow, continual enlargement of the prostate gland, affects nearly all older men, although not all display symptoms. Close to 90 percent of men older than 85 have microscopic evidence of BPH, but only half of them will have clinical prostate enlargement. As the prostate enlarges, it compresses the urethra, the duct through which urine flows from the kidney. This compression may obstruct urine flow, causing weakened urination, urinary frequency (especially at night), urine retention, pain and possibly kidney damage.
The factors causing the prostate to enlarge are not fully understood. A leading theory involves the levels and activity of activated testosterone and/or dihydrotestosterone (DHT) in the prostate. The enzyme 5a-reductase converts testosterone to DHT. A pharmaceutical, finasteride, treats BPH by blocking this enzymatic reaction and lowering the amount of DHT in the prostate, which decreases prostate cell division and overgrowth of the gland. In vitro evidence shows saw palmetto extracts also inhibit 5a-reductase activity, though its action is about 60 times weaker than that of finasteride. [1-3]
In an effort to more reasonably explain how saw palmetto reduces symptoms, other mechanisms of action also have been proposed.
It appears saw palmetto extracts inhibit DHT from binding to cellular receptors, which would be another way to decrease DHT's ability to make prostate cells grow. Such an effect has been demonstrated through in vitro experiments. 
This is a benefit beyond finasteride, which only has been shown to block 5a-reductase activity and thus lower the conversion of testosterone to DHT.
Saw palmetto also has demonstrated in vitro spasmolytic effects on muscle tissues. One effect of BPH is increased smooth-muscle tone of the urethra and other pelvic floor muscles. This increased muscle tone may contribute to urethral spasm, which would explain some BPH symptoms. It is conceivable, although unproven, that saw palmetto extracts may relax these pelvic muscles and thereby reduce BPH symptoms. 
Another theory is that saw palmetto extracts reduce estrogenic activity in the prostate. Estrogen contributes to BPH because it increases intracellular DHT levels by slowing its elimination. Researchers at the University of Rome, with a double-blind, placebo-controlled study, demonstrated that the anti-estrogenic and anti-androgenic actions exerted by saw palmetto extracts occur locally within the prostate, leaving serum levels of testosterone and estrogen unaffected. 
It is probable that multiple mechanisms contribute to saw palmetto's effects. For example, the herb's anti-inflammatory properties are no doubt part of the equation. Saw palmetto extracts have been shown in vitro to inhibit the production of inflammatory prostaglandins and leukotrienes.  This effect could significantly reduce prostatic inflammation and BPH symptoms, since the condition is associated with non-infectious inflammation. The swelling that results from this inflammation could explain the enlargement and some BPH symptoms.
Regardless of the mechanisms of action, numerous clinical trials support the effectiveness of saw palmetto extracts for treatment of BPH. There have been at least seven randomized, double-blind, placebo-controlled trials, and all but one had positive outcomes in terms of reducing urinary frequency, increasing urinary flow rate and reducing post-void residual urine volume.  However, none of the studies included a one-year follow-up, which is considered necessary to establish true efficacy.
One double-blind, placebo-controlled study in Britain enlisted 110 outpatients with BPH. Half the patients received 160 mg standardized extract of saw palmetto twice daily and half received placebo. Patients were evaluated and among those receiving saw palmetto, subjective improvement was noted to be "significantly superior" compared with those receiving placebo. Also, among the patients who received the herbal extract, statistically significant effects were observed in decreased nocturnal urination frequency, increased flow rate and decreased post-void residual volume. Oddly, there were fewer side effects reported from the saw palmetto group than the placebo group. 
A large, international, double-blind trial by French researchers at Pierre Fabre Medicament, La Chartreuse, Castres, compared saw palmetto extract to finasteride. For six months 1,098 patients with moderate BPH took 320 mg of saw palmetto daily or 5 mg finasteridethere was no placebo group. Both treatments were equally effective, but while the drug caused slight worsening of sexual function and lower levels of prostate-specific antigen (a hormonal marker), the herbal medicine did not cause side effects.  Although this trial suggests a positive effect from saw palmetto, it is flawed because there was no placebo group, and the length of the trial was less than one year. (Finasteride becomes more effective after six months to one year of use.)
Judging from the historical uses of saw palmetto as well as the current in vitro and clinical research data, the efficacy of the herb is undeniable. Although its mechanism of action is not yet fully understood, saw palmetto extracts are clearly effective at reducing BPH symptoms. The dose used in all of the studies is 160 mg twice daily of the liposterolic extract, which contains 85 to 95 percent free fatty acids (see table). This concentration corresponds to a dose of 34 g of dried berries daily.
There are relatively few side effects with saw palmetto therapy. Minor adverse effects such as headache, gastrointestinal discomfort, insomnia, dizziness and myalgia have been reported. High doses may cause diarrhea. Patients with hormone-dependent cancer should seek consultation from their doctor before taking saw palmetto.
As more information about this herb's mechanisms of action are uncovered, its efficacy in other conditions such as fibrocystic breast disease, impotence, chronic bladder infections and irritations, and general debility should be explored. Until then, using saw palmetto to treat BPH may be for many men a safe and effective alternative to prescription medications and surgery.
Saw Palmetto Breakdown
Commission E Monograph: Saw Palmetto Berry
Lise N. Alschuler, N.D., is the clinical medical director at Bastyr University, Bothell, Wash. She also has a private practice in Seattle.
1. Bombardelli E, Morazzoni P. Serenoa repens (Bartram) J.K. Small. Fitoterapia 1997;LXVIII(2):99-114.
2. Cristoni A, et al. Chemical and pharmacological study on hypercritical CO2 extracts of Serenoa repens fruits. Fitoterapia 1997;LXVIII(4):355-8.
3. Bone K. Saw palmettoa critical review. Euro J Herbal Med 1998;4(1):15-24.
4. DiSilervio F, et al. Evidence that Serenoa repens extract displays an antiestrogenic activity in prostatic tissue of benign prostatic hypertrophy patients. Euro Urol 1992;21(4):309-14.
5. Gutierrez M, et al. Spasmolytic activity of a lipidic extract from Sebal serrulata fruits: further study of the mechanisms underlying this activity. Planta Medica 1996;62(6):507-11.
6. Paubert-Braquet M, et al. Effect of the lipidic lipidosterolic extract of Serenoa repens (Permixon) on the ionophore A23187-stimulated production of leukotriene B4 (LTB4) from human polymorphonuclear neutrophils. Prostaglandins Leukot Essent Fatty Acids 1997 Sep;57(3):299-304.
7. Champault G, et al. A double-blind trial of an extract of the plant Serenoa repens in benign prostatic hyperplasia. Brit J Clin Pharmacol 1984;18:461-2.
8. Carraro J, et al. Comparison of phytotherapy (Permixon) with finasteride in the treatment of benign prostate hyperplasia: a randomized international study of 1,098 patients. Prostate 1996 Oct;29(4):231-40
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