Nature's Pharmacopeia: A World of Medicinal Plants

SAW PALMETTO

Serenoa repens

The saw palmetto is a low-growing palm abundant in its native range in eastern North America, along the coastal plains of South Carolina, Georgia, Florida, Alabama, and Mississippi.33 The plant grows in the shrub layer of the forest ecosystem and as scrub on sandy coastal dunes, reaching a height of 1 to 2 meters, with branching stems close to the ground and fan-shaped divided green or blue-green leaves as large as 1 meter in diameter (figure 14.5). Numerous small flowers in the spring yield black grape-size fruits (called berries) in the autumn.34 Saw palmetto has long been valued for its economically useful fibers, from which indigenous people made baskets and roof thatch, as well as for its slightly sweet, calorie-rich fruit.35 However, early European visitors to today’s Florida did not share the local peoples’ appreciation for saw palmetto berries, one seventeenth-century English writer describing their flavor as “rotten cheese steeped in tobacco.”36

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FIGURE 14.5   A stand of saw palmetto.

While saw palmetto was employed in traditional medicine among native North Americans for a wide variety of concerns, from respiratory to reproductive, it was not until the nineteenth century that saw palmetto came under the scrutiny of early biomedical science.37 Literature from that time documents the ways that doctors and pharmacists experimented with saw palmetto berry juice, fluid extract, and oil, taken orally or as a suppository (figure 14.6). Medical entrepreneurs also concocted numerous patent medicines combining saw palmetto with sandalwood (Santalum spp.) oil, coca (Erythroxylum coca) leaf, cola (Cola spp.) nut, parsley (Petroselinum crispum), and other ingredients.38 Late-nineteenth-century physicians recommended saw palmetto, in its various forms and preparations, for hemorrhoids, headaches, inflammation, bronchitis, gonorrhea, and a suite of other ailments of the male and female urogenital systems.39 Much attention was paid to saw palmetto’s effects on the sexual organs and on the breasts, for which doctors considered it “a great vitalizer, tending to increase their activity, to promote their secreting faculty, and add greatly to their size.”40

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FIGURE 14.6   An advertisement for Metto, a patent medicine that contained saw palmetto. (From Ocala [Fla.] Evening Star, July 27, 1901)

After a series of curious trials on themselves and their patients, saw palmetto researchers at the turn of the twentieth century lauded its effects in increasing female bust size, improving male libido and the quality of the erection, and particularly treating the prostate gland.41 While the prostate plays an important role in the male sexual response by secreting part of the seminal fluid, its position at the base of the bladder and tendency to enlarge with age can contribute to difficult and frequent urination in older men. The use of saw palmetto extract, doctors believed, reduced the size of the enlarged prostate and alleviated the urinary symptoms in their patients.

It is now recognized that certain fat-soluble chemicals (sterols and fatty acids) in the saw palmetto berry can interact with the normal pathways of testosterone and estrogen signaling, a finding that might help explain the plant’s therapeutic properties.42 Among several loci of action, saw palmetto fatty acids can inhibit the enzyme responsible for converting the steroid hormone testosterone to dihydrotestosterone, which is implicated in the (noncancerous) cell proliferation that increases the prostate’s size in older men.43 Numerous laboratory studies have demonstrated saw palmetto extract’s ability to reduce prostate cell growth in response to normal hormonal stimuli.44

Controlled clinical studies of saw palmetto’s effects on urinary symptoms associated with prostate enlargement have generated a rather large volume of literature, but evidence clearly demonstrating its therapeutic efficacy has not yet emerged. While some relatively small-scale trials using various types of extracts and methodologies have shown improved urinary symptom measures in patients treated with saw palmetto for durations of one to three months, the different experimental strategies make it difficult to generalize and compare outcomes.45 A recent meta-analysis of large-scale trials, applying strict criteria for quality of experimental design, found no significant difference in urinary symptoms or prostate size of patients with enlarged prostate between groups taking saw palmetto extract at various common doses or those taking a placebo.46 Despite laboratory results demonstrating saw palmetto extract’s mode of action on the hormonal processes regulating cell physiology, clinical trials taken collectively failed to show a convincing effect, highlighting the importance of ongoing research to understand better how herbal drugs enter the human system, whether and how they reach their proposed target tissues, and what activities they retain when there. The paucity of conclusive evidence notwithstanding, saw palmetto extract has become widely employed in Europe and North America.47

Types of biomedical herbal research data

Laboratory studies test pharmaceutical effects on isolated cell components, cells, or tissues in a test tube or Petri dish (called in vitro research) or in captive animals (in vivo research).

Clinical trials administer chemical preparations to human volunteers and record various physiological measures, noting side effects.

Meta-analyses use defined selection criteria and advanced statistical methods to draw conclusions from the results of numerous aggregated research reports.

While saw palmetto extracts are generally well tolerated, with few reported side effects, the commercial products available have been prepared to differing standards and vary tremendously in chemical composition.48 Therefore, any physiological effects of a saw palmetto extract would depend on the particular dose, formulation, and processing employed in its manufacture.

Hallmarks of good experimental design

•    Large sample size to reduce risk of test subjects unrepresentative of general population

•    Randomization of individuals receiving various experimental treatments

•    Blinding of researchers to the identity of the treatment groups

•    Credible placebo treatment to account for nonpharmacological effects