Beta-Sitosterol

What is beta-sitosterol?

Beta-sitosterol is one of the most common plant sterols, compounds with a structure similar to cholesterol. It is found in vegetable oils, nuts, seeds, avocados and legumes, and it is a major sterol in pumpkin seeds, saw palmetto and pygeum. Supplements are usually extracted from soy, pine or other plant sources. Plant sterols are also added to some margarines and foods because they reduce cholesterol absorption from the gut.

What the research says

Enlarged prostate symptoms

A Cochrane review, also published in the BJU International, pooled four randomized, double-blind trials with 519 men with benign prostatic hyperplasia, lasting 4 to 26 weeks. Compared with placebo, beta-sitosterol improved the International Prostate Symptom Score by about 4.9 points, increased peak urine flow by about 3.9 mL per second and reduced the urine left in the bladder after voiding by about 29 mL. It did not shrink the prostate. Dropout rates were similar to placebo (Wilt et al., 2000; Wilt et al., 1999).

The reviewers stressed important limits: the trials were short, used different and non-standardized preparations, and long-term effectiveness, safety and ability to prevent complications such as urinary retention or surgery were unknown. Most of these trials are now decades old, and few new placebo-controlled studies have been published.

Cholesterol

Plant sterols as a group reduce LDL cholesterol when taken in gram amounts with meals, which is why they are added to fortified foods. Doses in prostate supplements are usually much smaller.

How it might work

Proposed mechanisms include effects on inflammation and prostaglandins in prostate tissue and possibly on hormone metabolism, but these are not well established in people.

Putting it in context

Beta-sitosterol is one of the few prostate-support ingredients with pooled evidence from placebo-controlled trials, and the size of the symptom improvement in those trials was meaningful. Still, the evidence base is small and old, and men whose symptoms are bothersome or getting worse should discuss proven medical options with a doctor. Beta-sitosterol is also naturally present in other prostate ingredients such as pumpkin seed and pygeum, so combination products may supply it from several sources.

How it’s used in supplements

Beta-sitosterol is sold alone in capsules and is a staple of prostate formulas, often labeled as a “complex” or “plant sterols” that contains beta-sitosterol along with campesterol and stigmasterol. Because the label amount may refer to the whole sterol mix, the actual beta-sitosterol dose can be lower than it looks. It is generally well tolerated, with occasional digestive upset. People with sitosterolemia, a rare inherited disorder, should avoid it. Men should have urinary symptoms evaluated by a doctor and mention beta-sitosterol if they take prostate or cholesterol medicines.