Saw palmetto, Serenoa repens, also known as the American dwarf palm tree, grows wild in the southern states of the USA especially in Florida and Georgia. It is an evergreen shrub, grows up to 3 metres tall and has fan-shaped leaves. The plant was used as a food by the Native American populations in Florida and even today is still used as a food by Seminole people; a sweetened traditional drink ‘shiope sofkee’ is made from its juice.
Although saw palmetto has been used for a variety of medicinal purposes by Native Americans, it is now almost exclusively used to treat benign prostatic hyperplasia. It is easily the most commonly used herbal preparation for this condition worldwide and in some European countries it is regarded as the first-line treatment for this condition and is considerably cheaper than conventional drugs. It is the fruit of the plant that is used in modern dietary supplements and herbal medicines. It is consumed as a dried ground fruit or as an extract of the lipid fraction where the pharmacological activity is thought to be found. Teas made from saw palmetto are consumed, but as the active ingredients are believed to be lipid soluble these will contain little of these ingredients. The lipid extract contains plant sterols (phytosterols), numerous free fatty acids and monoglycerides.
Benign prostatic hyperplasia (BHP) and saw palmetto
Benign prostatic hyperplasia (BHP) is an enlargement of the prostate gland that frequently occurs in older men. Perhaps a third of men in their seventies have symptomatic BHP. The enlarged prostate gland can interfere with the voiding of urine, which can produce a range of symptoms such as:
• Difficulty in starting urination even when the bladder is full
• Incomplete bladder emptying or the sensation of incomplete emptying
• Slow flow of urine
• Dribbling of urine after urination
• Increased frequency of urination including during the night
• Urgency of urination
• Discomfort when passing urine.
Occasionally this condition can result in acute chronic retention where the patient is unable to pass urine even when the bladder is painfully full; this requires urgent catheterisation.
Neither the exact causes of benign prostatic hyperplasia nor the mode of action of saw palmetto in its relief have been unequivocally established. It has been suggested that saw palmetto extracts might work by blocking adrenergic receptors (specifically the a1-adrenoreceptor) in the prostate causing muscle relaxation and so assisting the passage of urine. Although saw palmetto extracts have been shown to have antagonistic effects upon these receptors in vitro, Goepel et al. (2001) suggest that therapeutic doses of saw palmetto do not cause this effect in vivo in men. An alternative suggestion and one that is currently favoured is that saw palmetto extracts inhibit the enzyme (5-alpha reductase) that converts testosterone to its more active form dihydrotestosterone – this effect has been demonstrated in isolated human prostate cells. Dihydrotestosterone stimulates growth of the prostate and there is speculation that hormonal imbalances in older men may be the cause of this prostatic hyperplasia. Saw palmetto may exert an anti-androgenic effect by blocking the binding of dihydrotestosterone to the androgen receptors in the prostate. Other less documented pharmacological actions of saw palmetto are listed in the United States Pharmacopeia.
There have been many clinical trials of saw palmetto for the treatment of BHP and several systematic reviews. Wilt et al. (2000) identified 18 randomised trials of saw palmetto with a total of almost 3000 participants. Some trials compared saw palmetto with placebos in double-blind trials and some compared it to finasteride (a drug widely used to treat BHP (benign prostatic hyperplasia), which is a known 5-a reductase inhibitor). The main outcome measure was the patients’ own assessment of their urinary symptoms using a standard validated scale. They concluded that the then available evidence suggested that saw palmetto performed significantly better than the placebo in reducing urological symptoms and improving urine flow. Its effects were comparable to those of the commonly used drug finasteride but the saw palmetto was cheaper and better tolerated with less adverse symptoms and fewer patient withdrawals. An update of this review added three further trials but essentially confirmed the original findings that saw palmetto provides mild to moderate symptomatic relief from the symptoms of BHP with few adverse effects. None of the trials that were reviewed lasted longer than 48 weeks so the long-term safety could not be established.
The standard dosage of saw palmetto is 320 mg/day of the lipid extract taken in two aliquots each day or 1-2 g of the dried fruit.
Note that whilst the evidence suggests some clinically useful benefit of this herb, self-medication should not be attempted without proper diagnosis of the condition and consultation with a physician. Some of the symptoms of benign prostatic hyperplasia are common to prostatic cancer and other conditions. This general rule should apply for the use of supplements in most other conditions as well.