Saw palmetto no more effective than placebo for urinary symptoms

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NIH-funded study finds dietary supplement does not alleviate BPH

Saw palmetto, a widely used herbal dietary supplement, does not reduce urinary problems associated with prostate enlargement any better than a placebo, according to research funded by the National Institutes of Health. The study was published Sept. 28 in the Journal of the American Medical Association.

Prostate enlargement, also called benign prostatic hyperplasia (BPH), can cause frequent urination, a weak or intermittent urine stream and an inability to empty the bladder completely. More than half of men in their 60s, and up to 90 percent in their 70s and 80s, have symptoms of BPH.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the National Center for Complementary and Alternative Medicine (NCCAM) and the Office of Dietary Supplements (ODS) supported the study. All are part of the NIH.

According to Robert A. Star, M.D., director of the NIDDK's Division of Kidney, Urologic and Hematologic Diseases, the current study met an important need for rigorous evaluation of standard and higher doses of saw palmetto. The trial also confirmed results of the earlier NIDDK- and NCCAM-sponsored Saw Palmetto Trial for Enlarged Prostates (STEP), which found that a standard daily dose of 320 milligrams provided no greater symptom relief than placebo.

"Investigators designed the current trial to determine whether daily doses of up to 960 milligrams — three times the standard daily dose — would prove better than a placebo at improving lower urinary tract symptoms in men due to BPH," said Star. "We were disappointed to find that higher doses of saw palmetto did not improve symptoms more than placebo."

Josephine P. Briggs, M.D., director of NCCAM, added that this study further illustrates the importance of conducting research on botanical products that are used extensively by the general public.

"This was a well-designed study that addressed limitations of earlier, smaller trials — it was a multicenter study with a larger sample size and tested different doses of a carefully analyzed saw palmetto product," Briggs said. "The NIH is committed to bringing rigorous science to the study of natural products and to building the evidence base that can guide consumer decisions."

The study was a double-blind randomized placebo-controlled clinical trial conducted at 11 North American clinical sites from June 2008 to October 2010. A cohort of 369 men aged 45 years or older participated, each with a peak urine flow rate of at least four milliliters per second at the beginning of the study — which is less than normal. Also, all had an American Urological Association Symptom Index (AUASI) score of between eight and 24 — a lower score is better. The AUASI score ranges from zero to 35. Escalating doses of saw palmetto or placebo were given, starting at one, then two, and then three pills of 320 milligrams per day, with dose increases at 24 and 48 weeks.

The study measured the differences between the AUASI score at the start of the trial and after 72 weeks of treatment. Secondary measures included improvements in frequency, nocturia (nighttime urination), peak urine flow, prostate-specific antigen (PSA) level, sexual function, incontinence and sleep quality.

Between baseline and 72 weeks, mean AUASI scores decreased from 14.4 to 12.2 points with saw palmetto extract and from 14.7 to 11.7 points with placebo. The group average change in AUASI score from baseline to 72 weeks between the saw palmetto and placebo groups was 0.79 points, favoring placebo. Saw palmetto was not more effective than placebo in reducing urinary symptoms for any of the secondary outcomes.

According to Joseph M. Betz, Ph.D., director of the Analytical Methods and Reference Materials program at ODS and a study co-author, the study used a very well-characterized saw palmetto product. Through batch testing, study investigators took extreme care to ensure that the composition of the supplement was consistent over the whole study.

"Saw palmetto and other herbs are often manufactured in different ways, so no two brands are likely to have the same composition," Betz said.