Sterols and sterolins are also known as phytosterols or plant sterols, and phytosterolins or plant sterolins. Other synonyms include sitosterols or sitosterolins, and beta sitosterols or beta sitosterolins. The easiest way to categorize these molecules is to remember that they are the equivalent of plant cholesterols. They are very similar in structure to human cholesterol, but are not found in the plant world; such plant sterols and sterolins are not produced in humans. 
There are over 40 different plant sterols. The most abundant is beta-sitosterol. It comprises about 50% of the sterols found in plants.
Plant sterols are believed to enhance the immune system, lower lipid levels, treat BPH, and be anti-tumor. They also possess certain anti-inflammatory and antimicrobial actions.
All plants contain sterols and sterolins. The typical dietary intake of sterols from the recommended five fruits and vegetables equates to roughly 100 - 300 milligrams (mg) per day. Today plant sterols can also be found in margarine, spreads, and dressings. 
Many of the medicinal botanicals are high in plant sterols, including Saw Palmetto, Pumpkin Seed, and Pygeum africanum. In many cases the active compounds in these herbs that help to achieve the desired effect are the sterols.
- Plant sterols are effective at lowering the lipids in the blood. They have been shown to decrease LDL cholesterol. The mechanism of action is believed to be by means of decreased absorption in the gut, and displacement from the bile acids in the GI and carrier molecules in the blood. 
- Plant sterols, in particular Beta-sitosterol, are an effective treatment for BPH (benign prostatic hyperplasia). Numerous studies have shown that beta-sitosterol decreases the symptoms associated with this condition. 
- Beta-sitosterol has also been proven to be anti-tumor. It has chemoprotective action against colon and breast cancers in various animal models. It is believed to be effective at inhibiting invasion of the cancer cells into surrounding tissue, while preventing metastasis. 
- Plant sterols may also be effective at treating Rheumatoid arthritis and SLE (Systemic Lupus Erythematosus), due to its anti-inflammatory action. 
- Plant sterols are believed to stimulate the production of white blood cells and enhance immunological function. These actions may or may not make plant sterols effective as an adjunct treatment for infection.
The typical dosage for treating BPH is 10 - 65 milligrams of beta-sitosterol, three times a day. Dosages of 1 gram a day of plant sterols can be used to achieve desired effects on the immune system and cholesterol lowering effects.
- Side effects include indigestion, constipation, diarrhea, gas, and bloating.
- Ingestion of plant sterols is contraindicated in those individuals who suffer the rare genetic disease, phytosterolemia. These persons cannot metabolize the sterols correctly.
- Plant sterols are also contraindicated in women who are pregnant or nursing due to the ability to interfere with cholesterol absorption.
1. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Phytosterols. March 2005.
2. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Phytosterols. March 2005.
3. DeVaraj S et al. Plant sterol fortified orange juice effectively lowers cholesterol levels in mildly hypercholesterolemic healthy individuals. Arterioscler Thromb Vasc Biol. 2004 Mar; 24(3): e25-28.
4. Berges RR, Kassen A, Senge T. Treatment of symptomatic benign prostatic hyperplasia with beta-sitosterols: an 18-month follow-up. BJU Int. 2000 May; 85(7): 842-846.
5. Ovensa Z, Vachalkova A, Horvathova K. Taraxasterol and beta-sitosterol: new naturally compounds with chemoprotective/chemopreventative effects. Neoplasma. 2004; 51(6): 407-414.
6. Monograph: Plant sterols and sterolins. Altern Med Rev. 2001 Apr; 6(2): 203-206.
7. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Phytosterols. March 2005.