Saw palmetto fruits, once used as food, are benign. Clinical trial evidence supports its efficacy for treating benign prostatic hyperplasia (BPH); prostate-specific antigen (PSA) is not affected.
[LFODPKM ] Letter Key
Latin Name
Serenoa repens [Bartr.] Small, syn. S. serrulata [Mich.] Hook f., Sabal serrulata [Mich.] Nuttall ex Schult.
Family
Palmae/Arecaceae
Other Common Names
Dwarf American palm
Description
- Saw palmetto, the most common palm in the United States, is 6 to 10 ft tall and has fan shaped, deeply divided leaves up to 1 m in width, and black fruits. Its branching stems are unusual in a palm (1). Saw palmetto grows throughout Florida, north to South Carolina, and west to Texas. It provides food or cover for more than 100 bird, 27 mammal, 25 amphibian, and 61 reptile species (1).
Part Used
Dried ripe fruit
Known Active Constituents
-Sitosterol and its glucoside, stigmasterol, and campesterol are thought to be the most important constituents (2). High molecular weight fatty alcohols (especially docosanol, hexacosanol, octacosanol, and triacontanol) also appear to be important (2). The purified lipid extract contains 85% to 95% fatty acids and sterols (including -sitosterol, stigmasterol, cycloartenol, lupeol, lupenone, and methylcycloartenol) (3). Free fatty acids (including capric, caprylic, caproic, lauric, palmitic, and oleic acids) compose nearly two thirds of the oil (1).
Mechanism/Pharmacokinetics
- The mechanism of Serenoa repens has not been well established. In vitro and in vivo studies indicate that saw palmetto inhibits binding of dihydrotestosterone (DHT) to androgen receptors.
- An antiestrogenic effect of saw palmetto was noted in a placebo-controlled trial of 35 men with BPH who received Serenoa repens 160 mg b.i.d. (4). Prostate cell nuclear fraction was positive for estrogen receptors in only 1 of 18 men receiving active therapy versus 14 of 17 men on placebo (the cytosolic fraction was estrogen receptor positive for 12 men in each group).
- Saw palmetto may competitively block translocation of estrogen receptors from the cytosol to the nucleus.
- In vitro studies are mixed on whether or not saw palmetto extracts inhibit 5
-reductase (5,6), but no evidence of 5-alpha-reductase inhibition was noted in 32 healthy men treated with 320 mg Permixon for 1 week (7). - A potent 1-adrenoceptor effect of saw palmetto extract was noted in vitro (8).
- In rats, saw palmetto concentrates to a higher extent in the prostate than in other genitourinary tissues or liver (4).
[Outline]
[CAO ] Letter Key
Clinical Trials
- A systematic review of randomized trials of Serenoa repens in symptomatic BPH identified 18 randomized controlled trials (16 double-blind) that included a total of 2,939 men (9). Trials were 4 to 48 weeks in duration; the average study duration was 9 weeks. Ten trials were placebo-controlled, two drug-controlled, one compared Serenoa repens with another herb and active control, one compared active control with a mixture containing Serenoa repens, and one bioequivalence study compared an oral formulation with a rectal suppository. Compared with placebo, those treated with saw palmetto experienced decreased urinary tract symptom scores (weighted mean difference 1.41 points), decreased nocturia (weighted mean difference 0.76 times for evening), improvement in self rating of urinary tract symptoms (risk ratio for improvement 1.72), and improved peak urine flow (weighted mean difference 1.93 mL/second).
- A meta-analysis of all published clinical trial data on Permixon (a standardized lipid-sterolic extract) in patients with BPH identified 11 randomized clinical trials and two open-label trials that enrolled a total of 2,859 patients and lasted from 21 to 180 days (10). Nine of these trials are covered in the Wilt systematic review discussed previously. Seven trials were placebo-controlled, three compared Permixon with pharmaceutical drugs (finasteride, prazosin and alfuzosin), and one three-armed trial compared Permixon with Pygeum africanum extract (Tadenan) and placebo. Common endpoints were peak urinary flow rate and nocturia. Compared with placebo, Permixon caused a significantly higher improvement in peak flow rate, increasing flow rates by 2.2 mL/second [95% confidence interval (CI) 1.2 to 3.2] and reducing nocturia by 0.50 episodes (95% CI 0.40 to 0.52).
- Drug-controlled trials included in the reviews above are summarized in the questions and answers section.
- A recent double-blind study, not included in the previous reviews, randomized 44 men with symptomatic BPH to placebo or a saw palmetto herbal blend. Each capsule contained saw palmetto lipoidal extract 106 mg, nettle root extract 80 mg, pumpkin seed oil extract 160 mg, lemon bioflavonoids extract 33 mg, and vitamin A as beta-carotene 190 IU for 6 months (11). Clinical parameters improved in both groups, with no difference between groups. However, in the saw palmetto group, prostate epithelial contraction in the transitional zone decreased significantly from 17.8% percent epithelium to 10.7%. The percent of atrophic glands increased from 25.2% to 40.9% after treatment, also a significant difference. No adverse effects were noted.
Animal/In Vitro
- In vitro, a liposterolic extract of Serenoa repens inhibits both type I and type II isoenzymes of 5-reductase, inhibits binding of DHT to androgen receptors in prostate cells (specifically the cytosol), and inhibits binding of [3H] DHT to its receptor in human foreskin fibroblasts (4).
- In hormone-treated castrated rats, a liposterolic extract of Serenoa repens inhibited the increase in prostate wet weight (12).
- Phytosterols (a mixture of -sitosterol, campesterol, and stigmasterol) do not appear to bind to estrogen receptors and do not stimulate transcriptional activity of human estrogen receptors in a recombinant yeast strain (13).
Other Claimed Benefits/Actions
- Hirsutism (in women)
- Aphrodisiac
- Diuretic
- Renal and bladder disorders
- Stimulate breast growth
- Digestion
- Ergogenic
- Lung disorders
[Outline]
Q: Does saw palmetto affect tests for prostate specific antigen?
A: No. PSA levels were assessed in at least three trials (11,14,15), none of which found an effect of saw palmetto on PSA.
Q: How does saw palmetto compare to drugs used to treat BPH?
A: No trials have compared saw palmetto to terazosin to date, but the herb has been compared with two other alpha-blockers and finasteride. A 3-week study in 63 patients with BPH compared saw palmetto (160 mg b.i.d.) to alfuzosin (2.5 mg t.i.d.) (16). Clinical symptoms, urinary flow rates, and residual urinary volume by transabdominal ultrasound were assessed. Both treatments significantly improved nocturia, daytime frequency, peak flow rates, mean flow rates and residual urinary volume, with no significant difference between groups. However, alfuzosin was significantly more effective than saw palmetto for total symptom score on Boyarsky’s scale, visual analog scale and on overall clinical impression.
A 12-week trial compared Permixon (2 tablets daily) to prazosin (4 mg/day) in 42 men; peak flow increased from 9.75 ± 7.29 mL/s to 11.25 ± 8.77 mL/s in the Permixon group, compared with 10.36 ± 7.86 mL/s to 10.83 ± 11.07 mL/s in the prazosin group. Episodes of nocturia decreased from 2.5 ± 1.17 to 2.3 ± 1.39 in the Permixon group compared with a change from 2.1 ± 1.61 to 1.7 ± 1.76 in the prazosin group (17). Results apparently favored prazosin, but no statistical analysis was done (4).
A double-blind randomized study compared 5 mg finasteride to Permixon 320 mg for 6 months in 1,098 men with moderate BPH (14). Permixon and finasteride were equivalent in decreasing the International Prostate Symptom Score, improving quality of life, and increasing peak urinary flow. Finasteride decreased prostate volume and serum PSA levels, whereas Permixon had no effect on either. Permixon was less likely to cause complaints of decreased libido and impotence.
Q: What other uses are there for saw palmetto?
A: Saw palmetto stems were once used as a starch, and the fruits were an important food for pre-Colombian people and Creek immigrants in Florida, although they are not uniformly popular. One correspondent described the taste as "rotten cheese steeped in tobacco" (1). Fibers have been used to make scrubbing brushes, roots were used for paper manufacture, leaves and stem fibers have been used as upholstery fill, and the stem was once used as a cork substitute. The fibers are also widely used in Seminole and Miccosukee crafts. Leaves are sometimes used as roof thatch.