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Beta-sitosterol for benign prostatic hyperplasia

Suppose you are an advisor to an active local group of Age Concern that comes to you with the question of whether ß-sitosterol is worthwhile for treating benign prostatic hyperplasia. After a mild panic, you have to admit that you've never heard of ß-sitosterol, but you'll have quick look to see whether there's anything in the literature.

A quick search of PubMed tells you that there's a recent systematic review [1], and what's more you can download it from the Internet. Now the real problems start, because you have to interpret this for some bright, interested, and concerned people. What can you usefully say?


Immediate confidence comes from the review itself. It comes from a specialist prostate group at the Veterans Association in the USA. It uses extensive searching, including specialist databases of herbal medicines, and the Cochrane Library, and Cochrane Prostate and Complementary Medicine organisations. So it might be supposed that this is a comprehensive search.

Then the inclusion criteria are specific. Only properly randomised trials were acceptable, and the authors show they were aware of pitfalls from improper randomisation, which can give rise to falsely optimistic results. The diagnosis of benign prostatic hyperplasia has to be by recognised symptom scoring, and what constitutes ß-sitosterol is clearly defined.

The outcomes are clearly defined. Symptom scoring is most important, with maximum urinary flow rate and residual volume and prostate size as secondary outcomes. The methods of analysis tell us that the reviewers know how to deal with difficult issues like incomplete reporting of continuous data (for instance where no standard deviations or errors are given with continuous data).


The first problem is that there were only four randomised trials with 519 men randomised. The second is that they all used different ß-sitosterol preparations. The third is that while three had lasted six months, one was of only four weeks. Given these problems, was there any benefit?

Three studies reported symptom scoring, and all showed significant benefits for ß-sitosterol over placebo. Three of four also showed significant benefits for peak urinary flow rate and three for residual volume. The study consistently showing no benefit was the smallest of the four.


Now comes the difficult bit: giving some advice to these bright older folk from Age Concern. There is a variety of problems you need to convey.

The problems are that ß-sitosterol comes in many different forms and there is simply no guarantee that anything used resembles any of the products in the trials. The review discusses the bewildering mixture of phytopharmacological extracts that can form ß-sitosterol, including whether or not the ß-sitosterol is glucuronidated or not. No mechanism of action is known, and there is no basic science to fall back on to help in evaluating the results.

There is some evidence of benefit, but there is still the possibility of residual bias. We are told about randomisation, but not about double blinding. [Note from the Editor: not so - the paper tells us that all the studies were double blind. It just shows how eagle-eyed one has to be when reading reviews and clinical trials] Unblinded studies can give falsely optimistic results. The numbers are pitifully small, with only 440 men studied for at least six months. There is no information given about possible harm, or interaction with other medicines likely to be taken by older people.

None of the studies compared ß-sitosterol with conventional pharmaceuticals. That means we just don't know how treatments compare. All the review tells us is that in two of the trials men had only moderately inconvenient symptoms.

So, much as it would be nice to be positive about this, the best we can manage is to advise caution. Caveat emptor . Ask the vendors for full information. Ask the vendors about possible harm. Ask the vendors how much they are spending on research and development to help answer these questions.


  1. TJ Wilt et al. ß-sitosterol for the treatment of benign prostatic hyperplasia: a systematic review. BJU International 1999 83: 976-983.
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