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Beta-Sitosterol and LDL

Beta-sitosterol is the most popular plant sterol used in traditional medicine. Among its many health benefits, it is known to lower cholesterol levels especially the level of LDL cholesterol. Studies have shown that this cholesterol-lowering effect is due to the similarity between the structures of beta-sitosterol and cholesterol. But how exactly does beta-sitosterol bring down serum cholesterol levels and what other cardiovascular benefits can be derived from this plant sterol? Read on to find out.
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What is Beta-Sitosterol?

Beta-sitosterol is one of the popular plant sterols with medicinal properties and it is structural similar to cholesterol.

It can be found in a wide variety of plants including herbs like saw palmetto and pygeum; fruits like cashew and avocado; as well as in wheat germ, rice bran, corn oils and soybeans.

Beta-sitosterol is one of the phytosterols used for lowering blood cholesterol levels. Both phytosterols and the related phytostanols work by inhibiting the uptake of cholesterol from the intestines. This is possible because they are all structurally similar to cholesterol.

Therefore, beta-sitosterol lowers cholesterol levels because it is structurally similar to cholesterol.

Basically, beta-sitosterol competes with cholesterol in the intestines. Therefore, it reduces the absorption of cholesterol.

Besides its importance in the treatment of hypercholesterolemia, beta-sitosterol is also used to reverse hair loss and treat prostate enlargement.

Common side effects of beta-sitosterol supplementation are nausea, indigestion, gas, constipation and diarrhea.

Beta-sitosterol consumption and supplementation are generally safe except for those with genetic disorders such as sitosterolemia (excessive storage of beta-sitosterol and related fats) and phytosterolemia (excessive absorption of phytosterols such as beta-sitosterol).

Although beta-sitosterol is not extensively absorbed, long-term use and high doses of beta-sitosterol supplements can result in high blood level of the sterol. The accumulation of beta-sitosterol in the body can cause coronary artery disease as sterols clog arteries much like cholesterol.

In addition, beta-sitosterol supplements are not recommended for those who have suffered from heart attacks. This is because studies have identified that high blood levels of beta-sitosterol can increase the risk of heart disease in such people.

How Beta-Sitosterol Lowers Cholesterol Levels
  • By reducing the absorption of cholesterol from the intestines; this leads to
  • Increased fecal excretion of dietary cholesterol
  • Upregulation of LDL receptors (increase in the population of LDL receptors) on the surface of liver cells
  • Increased uptake of LDL cholesterol into the liver leading to reduced blood level of LDL cholesterol

Studies on Beta-Sitosterol and Cholesterol

The cholesterol-lowering properties of beta-sitosterol has been repeatedly demonstrated over the last 50 years. The studies described below represent the highlights of the large body of scientific work done on the benefits of beta-sitosterol for lowering cholesterol levels and improving cardiovascular health.

Can Beta-Sitosterol Lower Cholesterol Levels?

One of the earliest studies investigating the cholesterol-lowering benefits of beta-sitosterol was published in the journal, Circulation, in 1956. In that study, the researchers gave 12 – 16 g/day of beta-sitosterol supplement to 15 young men who have previously suffered from myocardial infarction.

The results showed that beta-sitosterol reduced serum cholesterol and lipoprotein levels irrespective of the diets the men were eating, their weights or initial serum cholesterol levels.

A 1999 Swedish study also agreed with these conclusions. For this study, the researchers gave a group of volunteers a beta-sitosterol supplement while placing them on a low-fat diet.

At the end of the study (less than 1 month), the combination of the diet and beta-sitosterol lowered both total cholesterol and LDL (low-density lipoprotein or “bad”) cholesterol. Beta-sitosterol and the low-fat diet lowered total cholesterol by 15% and LDL cholesterol by 19%.

The researchers concluded that these results showed the combination of beta-sitosterol and dietary changes can significantly reduce cholesterol levels even without exercise

In another study published in the American Journal of Clinical Nutrition in 2000, researchers gave a group of volunteers phytosterol-containing margarine. At the end of 3 weeks, the sterol administered significantly reduced total cholesterol and LDL cholesterol levels in the participants even though it was given along with cholesterol-raising margarine.

A 1995 French study also confirmed that beta-sitosterol can lower cholesterol levels even without dietary changes and exercise.

This study was done at the Center for Human Nutrition in France. The researchers gave beta-sitosterol to healthy people with normal cholesterol levels for 1 month. The results showed that beta-sitosterol lowered cholesterol levels by 10%.

This result is remarkable for different reasons. First, it demonstrates that beta-sitosterol can reduce cholesterol levels even when they are within normal ranges. Secondly, it shows that the cholesterol-lowering ability of beta-sitosterol does not depend on dietary changes or exercise although these can help too.

In fact, long-term beta-sitosterol supplementation is not required to produce results. A couple of related Japanese studies published in the journal, Joshi Eiyo Daigaku Kiyo, confirmed this.

One study involved a group of healthy, young men while the other involved healthy, young women.

In both studies, beta-sitosterol was given for 5 days and the results of both studies showed significantly drop in cholesterol levels.

These results are remarkable because they showed that beta-sitosterol can reduce cholesterol levels quickly. This means that the therapeutic effects of beta-sitosterol are not cumulative and even indicates that it stops cholesterol very early in its journey through the body.

Secondly, the results showed that even in healthy, young people, beta-sitosterol can still reduce cholesterol levels.

This conclusion is important because a review of past studies done on the cholesterol-lowering ability of beta-sitosterol shows that the best results are obtained in people with high-cholesterol levels who eat high-fat/high-cholesterol diets.

This review was published in American Journal of Medicine in 1999 and it analyzed the results of 17 human studies done between 1951 and 1999 on the effects of beta-sitosterol on cholesterol levels.

The authors of this meta-analysis concluded that beta-sitosterol can reduce total cholesterol level by 10% and LDL cholesterol by 13%.

How Does Beta-Sitosterol Lower Cholesterol?

In a study conducted at the University of California in San Diego, researchers fed a group of men with 500 mg/day of cholesterol and then gave them beta-sitosterol supplements.

The results of this study was published in the American Journal of Clinical Nutrition in 1982. The researchers found out that beta-sitosterol reduced the absorption of cholesterol in the intestines by 42%. Therefore, they recommended the addition of dietary sources of beta-sitosterol to diets rich in cholesterol in order to reduce the absorption of cholesterol.

A lot of studies investigating the mechanisms by which beta-sitosterol lowers cholesterol provide support for this conclusion.

From the Finnish trial published in the journal, Clinical Chimica Acta, in 1988 to a review published in 1999 in the journal, Current Opinion Lipidology, researchers have conclusively demonstrated that beta-sitosterol promotes the excretion of cholesterol.

Therefore, increasing the fecal excretion of cholesterol is the major mechanism by which beta-sitosterol lowers blood cholesterol levels.

A 1997 study published in the Journal of Lipid Research detailed the processes by which beta-sitosterol prevented the absorption of dietary cholesterol.

This in vitro study investigated the handling of cholesterol and phytosterols (beta-sitosterol, stigmasterol and campesterol) by intestinal cells. The summary of the study is detailed in the table below.

How Beta-sitosterol Inhibits Cholesterol 
  • Blocks the transportation of cholesterol from the plasma membrane to the endoplasmic reticulum. This means that beta-sitosterol blocks the movement of cholesterol from the outer membranes of intestinal cells into the inner chamber. This blockage reduces the absorption of cholesterol.
  • Blocks the uptake of micellar cholesterol. Before cholesterol can be absorbed, it has to be packaged in a group of charged molecules called micelles. This ensures its solubility and increases its absorption.
  • Reduces the secretion of cholesteryl ester in the intestinal lumen. This is the form in which cholesterol is absorbed.
  • Reduces cholesterol synthesis by inhibiting the liver enzyme, HMG-CoA reductase.

Effect of Beta-Sitosterol on Lipid Oxidation

The ability to lower blood cholesterol level is not the only means by which beta-sitosterol improves cardiovascular health. Studies also show that beta-sitosterol can also inhibit lipid peroxidation.

Lipid peroxidation produces free radicals and reactive oxygen species that can damage cellular membranes and even oxidize LDL cholesterol.

A study published in the journal, Metabolic Brain Disease, in 2000 tested the effects of cholesterol, beta-sitosterol, melatonin and DHEAS (dehydro-epiandrosterone sulfate) on lipid peroxidation in an in vitro system.

The study showed that at low concentrations, beta-sitosterol (and even cholesterol) can reduce lipid peroxidation. However, at high concentrations, beta-sitosterol (much like cholesterol) can actually increase lipid peroxidation.

The results of this study suggest that high doses of beta-sitosterol should be avoided because at high concentrations beta-sitosterol actually worsens cardiovascular health.

This may well be the reason beta-sitosterol supplementation increases the risk of heart disease in men who have had previous heart attack.

Should Beta-Sitosterol Be Combined with Prescription Cholesterol-Lowering Drugs?

Although beta-sitosterol is not commonly prescribed for lowering cholesterol levels by doctors, there is overwhelming clinical evidence to support its use as a cholesterol-lowering agent. Therefore, there is an ongoing interest in finding out the benefits of combining beta-sitosterol with prescription cholesterol drugs.

A 1996 study published in the journal, Current Therapeutic Research, researchers recruited 30 patients with elevated cholesterol and triglyceride levels. For the first 16 weeks of the study, these volunteers were given the maximum doses of lovastatin they could tolerate.

For the next 12 weeks, some of these patients continued on lovastatin while the others added 6 g/day of beta-sitosterol.

The results showed that the levels of total cholesterol and LDL cholesterols decreased in all the volunteers after the 16-week period during which they were all placed on lovastatin.

However, the addition of beta-sitosterol lowered LDL cholesterol levels by 13% – 15%.

The results also showed that when beta-sitosterol was discontinued, the level of LDL cholesterol increased again.

This study indicates that beta-sitosterol may provide additional benefits when added to prescription cholesterol drugs especially those that lower cholesterol by other means.

Prescription cholesterol drugs that also reduce cholesterol absorption may not be combined with beta-sitosterol. For example, studies have shown that the combination of beta-sitosterol and ezetimibe (Zetia or Ezetrol) provided no additional benefits and might even be less effective than the individual medications.

Sources


http://www.webmd.com/vitamins-supplements/ingredientmono-939-BETA-SITOSTEROL.aspx?activeIngredientId=939&activeIngredientName=BETA-SITOSTEROL

http://www.drugs.com/npp/beta-sitosterol.html

http://prostate.emedtv.com/beta-sitosterol/beta-sitosterol.html

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