Chitosan is a form of fiber chemically processed from crustacean shells. Like other forms of fiber, such as oat bran, chitosan is not well digested by the human body. As it passes through the digestive tract, it seems to have an ability to bond with ingested fat and carry it out in the stool. For this reason, it has been tried as an agent for lowering cholesterol and reducing weight. However, the results in studies have been more negative than positive.

In addition, chitosan has been tried as a treatment for kidney failure and as an aid in wound healing.

Note: We do not recommend the use of chitosan in children or pregnant women due to concerns about possible delayed growth (see Safety Issues below).

Requirements/Sources

Chitosan can be extracted from the shells of shrimp, crab, or lobster. It is also found in yeast and some fungi. Another inexpensive source of chitin is "squid pens," a byproduct of squid processing; these are small, plastic-like, inedible pieces of squid that are removed prior to eating.

Therapeutic Dosages

The standard dosage of chitosan is 3 to 6 g per day, to be taken with food.

Chitosan can deplete the body of certain minerals (see Safety Issues below). For this reason, when using chitosan, it may be helpful to take supplemental calcium, vitamin D, selenium, magnesium, and other minerals.

Also, according to a preliminary study in rats, taking vitamin C along with chitosan might provide additional benefit in lowering cholesterol.1

Therapeutic Uses

On the basis of chitosan's supposed ability to bind fat in the intestines, it has been tried as a treatment for high cholesterol. However, the evidence regarding whether it really works is generally more negative than positive.31, 36,37,39,40, 42,43,45,48,49 At best, chitosan appears to offer no more than minimal benefit for high cholesterol.

Chitosan has also been proposed as a weight loss treatment on the same principle.2,3 However, despite some mildly positive results, the current balance of evidence suggests chitosan does not in fact significantly aid weight loss.4,5,37,41,44,46,49,50

Weak evidence hints that chitosan may be helpful in kidney failure.15 When used for this purpose, it is thought to work by binding with toxins in the digestive tract and causing them to be excreted.

Studies in dogs have found that topically applied chitosan can help heal wounds.16 This effect might be due to stimulation of new tissue growth; in addition, topical chitosan appears to kill bacteria such as Streptococcus, which may also contribute to wound healing.16 Chitosan may also have activity against Candida albicans, a form of yeast that causes vaginal infections.

Highly preliminary evidence suggests that oral chitosan may inhibit the expected rise in blood pressure after a high-salt meal.18 Other weak evidence hints that chitosan chewing gum might help prevent cavities.47

It has been suggested that chitosan can stimulate the immune system and prevent cancer,16 but there is no reliable evidence as yet that it offers these benefits.

Animal studies suggest that some forms of chitosan may help to prevent bone loss;20 however, because chitosan also interferes with mineral absorption, the net effect in humans might actually be to increase bone loss (see Safety Issues below).

What Is the Scientific Evidence for Chitosan?

An 8-week, double-blind, placebo-controlled trial of 51 women found that use of chitosan at a dose of 1,200 mg twice daily slightly reduced LDL ("bad") cholesterol as compared to placebo, but did not affect total or HDL ("good") cholesterol levels.37 Another 8-week trial, this one enrolling 84 people, also found modest benefits.39

However, a 4-month, double-blind, placebo-controlled trial of 88 individuals found no improvement in cholesterol with 1,000 mg 3 times daily of a different chitosan product.31 A 7-month study of 84 men given placebo or 1,200 mg of chitosan daily also failed to find benefit.43 Furthermore, in a 10-month, double-blind, placebo-controlled study of 130 men and women, use of a special microcrystalline form of chitosan at a dose of 1,200 mg twice daily again failed to improve cholesterol profile.40

These contradictory results suggest that if chitosan actually improves cholesterol profile at all, it does so to only a minimal extent.

Chitosan has been widely advocated as a weight loss supplement, on the basis of its supposed ability to bind fat in the digestive tract. However, despite some positive results 21,46 the largest and best designed trial failed to find benefit.41 In this 6-month, double-blind, placebo-controlled study of 250 overweight people, use of chitosan at a dose of 3 g daily failed to enhance weight loss to any meaningful extent as compared to placebo.

Other studies have also failed to find significant benefit.22, 37,44,49,50  

People with kidney failure experience numerous health problems, including anemia, fatigue, and loss of appetite. In one open study, researchers tested chitosan supplements in 80 people with kidney failure receiving ongoing hemodialysis treatment. Half the participants were given 45 mg tablets for a total of about 1,500 mg of chitosan daily for 12 weeks; the other half were not given a supplement.32 Those in the treatment group showed a significant decrease in urea and creatinine levels. Further, they had a rise in hemoglobin levels and reported improved overall strength, appetite, and sleep. However, these results must be taken with grain of salt, for only double-blind, placebo-controlled studies can prove a treatment effective. (For information on why this is so, see Why Does This Database Rely on Double-blind Studies?)

Safety Issues

There is significant evidence that long-term, high-dose chitosan supplementation can result in malabsorption of some crucial vitamins and minerals including calcium, magnesium, selenium, and vitamins A, D, E, and K.16,34 In turn, this appears to lead to a risk of osteoporosis in adults and delayed growth in children. For this reason, adults taking chitosan should also take supplemental vitamins and minerals, making especially sure to get enough vitamin D, calcium, and magnesium.

Another possible risk of long-term ingestion of high doses of chitosan is that it could change the intestinal flora and allow the growth of unhealthful bacteria.16

Finally, there has been a case report of arsenic poisoning caused by long-term use of chitosan supplements.38 Shellfish, it appears, can concentrate arsenic in their shells as part of their normal development; this in turn may lead to arsenic-laced chitosan supplements.

Pregnant or nursing women and young children should probably avoid chitosan altogether.