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Institute of Medicine (US) and National Research Council (US) Committee on the Framework for Evaluating the Safety of Dietary Supplements. Dietary Supplements: A Framework for Evaluating Safety. Washington (DC): National Academies Press (US); 2005.

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Dietary Supplements: A Framework for Evaluating Safety.

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Appendix KPrototype Focused Monograph: Review of Antiandrogenic Risks of Saw Palmetto Ingestion by Women1

I. DESCRIPTION OF THE INGREDIENT

A. Saw Palmetto as a Dietary Supplement Ingredient

Saw palmetto refers to Serenoa repens (W. Bartram) Small (Family: Arecaceae). An alternative name for the Arecaceae family is Palmae or Palmaceae. This plant is also known as (1) Serenoa serrulatum Schultes, (2) Serenoa serrulata (Michaux) Nichols, and (3) Sabal serrulata (Michaux) Nutall ex Schultes.

The medicinal part of saw palmetto is the fruit, which is about the size of a berry and is sometimes referred to as a “saw palmetto berry,” although it is a single seed drupe. The fruit is rich in carbohydrates and lipid components. The dried ripe fruit is typically the part of the plant used for dietary supplements.

B. Individual Components

Table A contains a list of the known components in extracts of saw palmetto fruit. Some components are common in many other plants and are widespread in the human diet. The components of extracts of saw palmetto fruit are commonly categorized as hexane extractable (i.e., phytosterols, phenolic components, free fatty acids, ethyl esters of fatty acids, and other lipid components), ethanol extractable (i.e., polyprenoids, flavonoid components, phenolic glycosides, and fatty alcohols), or water soluble (i.e., commonly found sugars and unique high-molecular-weight acidic polysaccharides). A hexane extract of saw palmetto fruit is the preparation that has been used most commonly in clinical trials. The hexane extract of saw palmetto fruit is unusual for a plant extract in that is has a very high content of medium-chain fatty acids and a high proportion of fatty acids present as ethyl esters.

C. Description of Dietary Supplement Preparations and Amounts Ingested in Ordinary Use

Saw palmetto is sold in several forms with lipid/sterol and “oily” extracts of the dried fruit being the most common forms on the market. A lipid/sterol extract of saw palmetto fruit (LESP) can be prepared by extraction with n hexane (100 percent), extraction with ethanol (70–95 percent, w/w), or by supercritical fluid extraction with liquid carbon dioxide. LESPs are somewhat quantifiable or standardized by total fatty acid content (usually 70–95 percent, w/w) or other components (USP, 2000). LESPs are commonly sold as capsules or tablets of a dried powder of the extract and in blended preparations where the powdered extract is combined with other ingredients, typically other powdered botanical extracts. Other forms of saw palmetto that may be available include powdered dried fruit (usually available in capsule or tablet form), dried whole fruit or preparations of the fruit (used in making a tea or water extract), tinctures (extracts made with aqueous ethanol as the solvent), and other liquid extracts.

In numerous clinical trials, the typical dose of saw palmetto for a subject with symptomatic benign prostatic hyperplasia (BPH)2 was 320 mg of LESP per day in 1 to 3 divided doses taken orally (or rectally in a few trials). The duration of ingestion of LESP varied from several weeks to several years.

II. SAFETY INFORMATION

A. Human Safety Data

1. Historical use

Historical use of saw palmetto for symptoms of BPH has been common in Asia and in native cultures in North America for centuries (Lowe, 2001; Wilt et al., 1998). Of the 30 plants known to have been used historically in phytotherapy for symptoms of BPH, saw palmetto has been the most widely used (Wilt et al., 1998). Historical uses were limited to saw palmetto in the form of the whole fruit, teas, aqueous extracts, and tinctures. They did not include lipid/sterol extracts of saw palmetto fruit such as those available in the current market.

In American Indian cultures, specifically in Florida, saw palmetto fruit was considered useful as a diuretic, sedative, aphrodisiac, nutritional tonic (due to the high oil content of the fruit), and to create a soothing vapor used as an expectorant. As American and European cultures learned about American Indian phytotherapy, the saw palmetto fruit came to be used to improve sexual vigor; to increase sperm production; as a mild diuretic; to relieve urinary difficulty, such as urgency-to-urinate and nocturnal enuresis in both men and women; and to improve urogenital disorders in women, such as ovarian enlargement and dysmenorrhea (Gennaro, 2000; Wilt et al., 1998).

Typically, the dried, ripe fruit is used for medicinal purposes. At times, the fresh fruit may be used; the safety of this practice has not been evaluated.

2. Adverse effects

Clinical trials: The clinical data for saw palmetto is primarily generated on male subjects. The one trial in women is in Table B, but there is no indication that pregnant women were included in this trial.

Spontaneous adverse event reports: Spontaneous reports related to possible effects in utero did not exist.

3. Interactions

Not applicable to the focus of this monograph.

B. Animal Studies

Animal studies: Only minimal classical animal toxicity data are available (Barsanti et al., 2000). These studies did not assess possible effects in utero or in offspring.

Table E summarizes information available from animal experiments related to antiandrogenic activity. In summary, in some model systems, antiandrogenic activity (specifically inhibition of hormonally or chemically induced prostate hyperplasia) can be demonstrated for extracts of saw palmetto fruit. In other model systems, no antiandrogenic activity was demonstrated.

TABLE E. Saw Palmetto: Summary of Animal Studies.

TABLE E

Saw Palmetto: Summary of Animal Studies.

C. In Vitro Studies

In vitro studies: Table F summarizes relevant information from in vitro experiments with saw palmetto. Inhibition of androgen-dependent proliferation and cellular stimulation have been demonstrated for extracts of saw palmetto fruit.

TABLE F. Saw Palmetto: Summary of In Vitro Studies.

TABLE F

Saw Palmetto: Summary of In Vitro Studies.

In vitro inhibition of testosterone metabolism through inhibition of steroid 5-α-reductase and 3-α-hydroxysteroid dehydrogenase was demonstrated. Inhibition of androgen binding was demonstrated in some model systems.

Classical in vitro toxicity data available are minimal (Degenring et al., 2001; Ondrizek et al., 1999a, 1999b) and do not address antiandrogenic concerns in females.

D. Related Substances

Table G contains information relevant to antiandrogenic safety issues for substances related to saw palmetto. Information about substances that are functionally related because they inhibit steroid 5-α-reductase is included. In summary, several of the substances functionally related to saw palmetto extract are contraindicated for use in women because of potential deleterious effects on the external genitalia and internal reproductive organs of the male fetus.

TABLE G. Saw Palmetto: Related Substances That Might Suggest Risk.

TABLE G

Saw Palmetto: Related Substances That Might Suggest Risk.

III. OTHER RELEVANT INFORMATION

A. Sources

The saw palmetto is one of the “fan palms”; it is also called the American dwarf palm tree or cabbage palm. The plant is sometimes called sabal and the fruit is called sabal fructus. This can be confusing because the saw palmetto is not a member of the genus Sabal; it is a distinct plant that can be confused with the Sabal palmetto. Other names for saw palmetto include shrub palmetto, juzhong, and palmier nain. Botanical descriptions of saw palmetto can be found in the literature (Leung and Foster, 1996).

Saw palmetto is an evergreen shrub, usually 2 to 10 feet tall. It is indigenous to undeveloped areas of the southern costal regions of the United States, especially Florida and Georgia, and is also abundant in Cuba and the Bahamas. Most saw palmetto fruit used in dietary supplements is harvested in Florida. It grows rapidly in sandy soil (either acidic or alkaline) and forms prominent colonies in sandy dunes, hammocks, or costal prairies. In the Northern Hemisphere, the plant blooms from April to early June and the fruit ripens in September and October.

Analytical issues: Saw palmetto was defined in the U.S. Pharmacopeia (USP) formulary in the early 1990s, but was eventually dropped. The 2002 National Formulary describes saw palmetto and powdered saw palmetto as preparations of partially dried, ripe fruit (USP, 2002). The USP requirements are voluntary, but must be met for any product bearing the USP designation. The USP formulary contains general tests for quality assurance3 and specific tests for saw palmetto or powdered saw palmetto4 (USP, 2000). Because these tests are voluntary, consumers have little assurance of product quality; variability in products is high (Feifer et al., 2002).

B. Relevant Conditions of Use Suggested or Recommended in Labeling or in Other Marketing Material

Occasionally, saw palmetto is marketed to women for urinary function, milk production during lactation, and, rarely, breast enlargement.

C. Cautions About Use

Cautions provided in labeling5 or other marketing material: A review of saw palmetto product labels and Internet marketing materials indicated that many (but not all) provide cautions to consumers to seek advice from health care providers before using the products if they have had prostate disorders or hormone-dependent cancers or are taking prescription medication, are pregnant, or are nursing. Some products carry warnings to discontinue use two weeks prior to surgery.

D. Usage Patterns

Total usage patterns and usage by men have been studied, but very little information is available about usage by women.

Saw palmetto has been used extensively in Europe and Asia. European sales figures for 1997 were $4 billion (Levy, 1998). In the United States, sales data reported by the Natural Marketing Institute ranked saw palmetto as the thirteenth best selling dietary supplement (Marra, 2002); however, sales growth has decreased 11 percent since 2001 (Marra, 2002). Sales for the U.S. market for saw palmetto supplements have been reported as $18 million in 1997 (Levy, 1998), $140 million in 1999 (Anon, 2000b), and $640 million in 2000 (Anon, 2000a). In a survey that examined the prevalence of use of herbal products among 752 randomly selected adults in Minnesota, saw palmetto was reportedly used by 4.3 percent of 376 respondents within the past 12 months to treat or prevent enlarged prostate, and to a lesser extent to promote general health and well-being and stimulate the immune system (Harnack et al., 2001).

It is estimated that 50 percent of men over the age of 50 have some symptoms of BPH (Berry et al., 1984). The incidence of BPH is 80 percent in men over the age of 80 (Berry et al., 1984). Urinary symptoms due to BPH result in 300,000 prostatectomies in the United States each year (Pinn, 2001). In a survey of patients in a U.S. urology clinic, 20 percent were combining conventional and botanical therapies, and 15 percent were using botanical dietary supplements alone (Bales et al., 1999). Over 30 percent of men with prostate problems have ingested saw palmetto for some period of time (Anon, 2000a).

E. Information on Regulation and Regulatory Actions

Foreign regulatory status: Saw palmetto is approved as a drug with prescription status in Austria, Italy, and Poland (Vallancien and Pariente, 2001). It is approved as a drug with over-the-counter drug (OTC) status for use in various urinary problems associated with BPH in Switzerland, Sweden, and Denmark. In Spain, standardized lipid/sterol extracts are approved as a drug with prescription status, and nonstandardized extracts are approved as dietary supplements. In France, saw palmetto has OTC status but is primarily prescribed by physicians. In Germany, the Commission E has evaluated saw palmetto as safe and effective for urination problems in mild to moderate BPH; extracts of saw palmetto fruit have OTC status but are primarily prescribed by physicians (Blumenthal, 1998). In Canada, saw palmetto is authorized for sale as a traditional herbal medicine with the indication of increasing the flow of urine.

F. Available Information on Physiological and Biochemical Aspects

Very little is known about the digestion, absorption, distribution, metabolism, and excretion of some components of saw palmetto fruit (i.e., phenolic components, phytosterols, flavonoids, and polyprenoids). Other components have been well characterized (i.e., sugars, fatty acids, and other hydrocarbons).

Distribution: In a study of rats given a radioactive n-hexane LESP, tissue concentrations of radioactive labeled isolates of lauric acid, oleic acid, and β-sitosterol were highest in abdominal fat tissue, prostate, and skin. Lower concentrations were distributed to the liver and urinary bladder (Chevalier et al., 1997). No other studies reporting on the distribution of components of saw palmetto fruit were identified. Saw palmetto components were not clearly identified in any reports found in the literature.

G. Supplementary Information

Rectal administration: Extract of saw palmetto fruit was administered rectally (De Bernardi di Valserra and Tripodi, 1994) to show that the bioavailability and pharmacokinetic profile was quite similar to oral administration. Tmax occurred about 1 hour after administration and a component was still detectable in plasma after 8 hours.

Topical use: A lotion containing cystine and saw palmetto extract is of possible use in alopecia (Morganti et al., 1998).

IV. TABLES ON SAW PALMETTO6

Table AIndividual Components of Saw Palmetto Fruit
Table BSaw Palmetto: Summary of Adverse Effects in Clinical Trials
Table CSaw Palmetto: Summary of a Clinical Case Reports (no relevant data available)
Table DSaw Palmetto: Summary of Adverse Event Reports (no relevant data available)
Table ESaw Palmetto: Summary of Animal Studies
Table FSaw Palmetto: Summary of In Vitro Studies
Table GSaw Palmetto: Related Substances that Might Suggest Risk

V. SUMMARY AND CONCLUSIONS

A. Summary

Saw palmetto is being widely used by men for prostate-related conditions, most notably benign prostate hyperplasia. Descriptions of saw palmetto are appearing in pharmacology texts for use in cystitis and for its antiedematous and antiandrogenic properties (Gennaro, 2000). There is a concern that these antiandrogenic properties pose a risk to males in utero because of the potential for deleterious effects on male genitalia.

Several pieces of evidence integrated together demonstrate that while there have not been documented cases of saw palmetto-induced birth defects in male offspring of humans or animals, there is a risk associated with saw palmetto ingestion by women.

It is well understood that testosterone, an androgen, or male sex hormone, is required for developing and maintaining masculine sexual characteristics. Testosterone is converted to the most active androgen DHT by 5-α-reductase, which then exerts the androgen action via androgen receptors.

In vitro data consistently demonstrate that saw palmetto extracts inhibit the testosterone conversion to DHT, including by inhibiting the 5-α-reductase enzyme. They also inhibit binding of DHT to androgenic receptors. Both of these actions would inhibit the androgen pathway if they occurred in vivo.

Animal data indicate that orally consumed saw palmetto preparations are antiandrogenic in vivo. Several animal studies were completed with oral administration of saw palmetto extracts following androgen stimulation of prostate hyperplasia. Studies indicate that saw palmetto extract at 50 to 300 mg/kg/day inhibit the androgen-stimulated hyperplasia in what appears to be a dose-dependent manner within studies. The 50 mg/kg/day is higher than the ~5 mg/kg/day ingested by humans (assuming 320 mg/day of LESP and 70-kg weight), but not high enough to mitigate concern for such serious effects as teratogenicity.

Inhibitors of 5-α-reductase are known to cause adverse effects and are thus contraindicated in women who may become pregnant (Table G). They are classified as pregnancy category X, the category indicating the greatest concern for pregnant women. As described in Table G, the pregnancy category X of these drugs results from teratogenicity studies in animals. These studies have shown that male offspring of animals (including monkeys) that consumed 5-α-reductase inhibitors exhibit abnormal male genitalia development.

Finally, the presumed mechanism for effectiveness of saw palmetto in prostate disorders is inhibition of androgen-sensitive pathways. This is partly because the prostate problems being investigated are generally treated by steroid 5-α-reductase inhibitors (Thomson PDR, 2004). Along these lines, the effect of saw palmetto on androgen pathways has also specifically been examined in humans. In a clinical study of healthy young males, no change in serum DHT was observed from ingesting the extract of saw palmetto fruit (320 mg/d, two divided doses, for 1 week) (Strauch et al., 1994). However, it was shown that activity of 5-α-reductase was decreased in prostate tissue and the content of DHT was markedly decreased in prostate tissue (mainly in the periurethral zone) in patients with benign prostatic hyperplasia who had ingested extract of saw palmetto fruit for 3 months.

The historical use of saw palmetto does not mitigate any concern about safety for pregnant women for several reasons. Most obvious is that saw palmetto has been predominantly used by men, and there is no indication that it has been safely used by pregnant women.

B. Conclusions and Recommendations About the Safety of the Ingredient Based on the Strength of the Scientific Evidence

At the present time, the weight of scientific evidence suggests that consumption of saw palmetto poses a risk to unborn male fetuses. This overall public health concern is mitigated somewhat by the much lower popularity of saw palmetto with women, but as noted previously, saw palmetto use is not limited to men. In summary, unless information becomes available to suggest that the antiandrogenic activity in humans is not high enough to cause birth defects in male offspring, a concern exists.

TABLE A. Individual Components of Saw Palmetto Fruit.

TABLE A

Individual Components of Saw Palmetto Fruit.

TABLE B. Summary of Adverse Effects in Clinical Trials Using Saw Palmetto in Blended Preparations.

TABLE B

Summary of Adverse Effects in Clinical Trials Using Saw Palmetto in Blended Preparations.

TABLE C. Saw Palmetto: Summary of a Clinical Case Reports (no relevant data available).

TABLE C

Saw Palmetto: Summary of a Clinical Case Reports (no relevant data available).

TABLE D. Saw Palmetto: Summary of Adverse Event Reports (no relevant data available).

TABLE D

Saw Palmetto: Summary of Adverse Event Reports (no relevant data available).

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Footnotes

1

This is a focused monograph, prepared for the purpose of illustrating how a safety review of a dietary supplement ingredient might be prepared following the format for focused monographs described in this report. While it was prepared as a prototype using the processes described in the report, it was not conducted under the auspices of the Food and Drug Administration utilizing all the resources available to the agency. Thus some pertinent information not available to the Committee could be of importance in evaluating safety to determine if use of this dietary supplement ingredient would present an unreasonable risk of illness or injury. Also, the development and review of this prototype was conducted by individuals whose backgrounds are in general aspects of evaluating science and whose expertise is not necessarily focused specifically on this dietary ingredient, although significant additional assistance was provided by consultants with relevant expertise. Therefore, this prototype monograph, while extensive, does not represent an authoritative statement regarding the safety of this dietary supplement ingredient.

2

BPH is a nonmalignant enlargement of the prostate from excessive proliferation, which causes nodules of the prostate gland to enlarge around the urethra, eventually limiting urinary flow from the bladder. Throughout life, dihydrotestosterone (DHT) directly stimulates the growth of the epithelial and stromal cells of the prostate. In aging men, the prostate is more responsive to androgen stimulation and the gland increases in size, causing urinary symptoms. Symptoms include difficulty in starting or stopping urine flow, a need to urinate frequently (especially at night), and a feeling of urgency-to-urinate. Urinary tract infections and urinary obstruction are common.

3

General USP tests for quality assurance are (i) foreign organic matter, (ii) loss on drying, (iii) total ash, (iv) acid-insoluble, (v) pesticide residues, (vi) heavy metals, and (vii) microbial limits.

4

Specific USP tests for saw palmetto or powdered saw palmetto are (i) botanic characteristics, macroscopic and microscopic (not applicable for powdered saw palmetto), (ii) identification, (iii) volatile oil content, (iv) content of lipophilic extract, and (v) content of fatty acids. The latter test includes identification of 11 USP methyl fatty acid RS standards (C6:0 through C18:3).

5

As defined in the Federal Food, Drug, and Cometic Act (FDCA) as currently amended, “The term ‘labeling' means all labels and other written, printed, or graphic matter (1) upon any article or any of its containers or wrappers, or (2) accompanying such article.” The term “label” is not being used; label means “a display of written, printed, or graphic matter upon the immediate container of any article” (FDCA, 21U.S.C. § 201(k) and (m)).

6

Tables appear at the end of this appendix.

Copyright 2005 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK216069

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