What are chitosan's therapeutic uses?

Overview

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.

Requirements and 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 by-product of squid processing; these are small, plastic-like, inedible pieces of squid that are removed before the squid is consumed.

Therapeutic Dosages

The standard dosage of chitosan is 3 to 6 grams (g) per day, to be taken with food. Chitosan can deplete the body of certain minerals. 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.

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. 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. However, despite some mildly positive results, the current balance of evidence suggests chitosan does not in fact significantly aid weight loss.

Weak evidence hints that chitosan may be helpful in kidney failure. 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. This effect might be caused by stimulation of new tissue growth; in addition, topical chitosan appears to kill bacteria such as those in the Streptococcus species, which may also contribute to wound healing. 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. Other weak evidence hints that chitosan chewing gum might help prevent cavities. It has been suggested that chitosan can stimulate the immune system and prevent cancer, 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; however, because chitosan also interferes with mineral absorption, the net effect in humans might actually be to increase bone loss.

Scientific Evidence

High cholesterol. An eight-week double-blind, placebo-controlled
trial of fifty-one women found that use of chitosan at a dose of 1,200 milligrams
(mg) twice daily slightly reduced low density lipoproteins (LDL, or bad
cholesterol) compared with a placebo but did not affect total or high density
lipoprotein (HDL, or good cholesterol) levels. Another
eight-week trial, this one enrolling eighty-four people, also found modest
benefits.

However, a four-month double-blind, placebo-controlled trial of 88 individuals found no improvement in cholesterol with 1,000 mg three times daily of a different chitosan product. A seven-month study of 84 men given a placebo or 1,200 mg of chitosan daily also failed to find any benefit. Furthermore, in a ten-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. These contradictory results suggest that if chitosan actually improves cholesterol profile, it does so to only a minimal extent.

Weight loss. 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, the largest and best-designed trial failed to find benefit. In this six-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, compared with a placebo.

Kidney failure. People with kidney failure experience numerous
health problems, including anemia, fatigue, and loss of appetite.
In one open study, researchers tested chitosan supplements in eighty 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
twelve weeks; the other half were not given a supplement. 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.

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. 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.

Finally, there has been a case report of arsenic
poisoning caused by long-term use of chitosan supplements.
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.

Bibliography

Bokura, H., and S. Kobayashi. “Chitosan Decreases Total Cholesterol in Women.” European Journal of Clinical Nutrition 57 (2003): 721-725.

Guha, S., et al. “Effect of Chitosan on Lipid Levels When Administered Concurrently with Atorvastatin.” Journal of the Indian Medical Association 103 (2005): 418, 420.

Ho, S. C., et al. “In the Absence of Dietary Surveillance, Chitosan Does Not Reduce Plasma Lipids or Obesity in Hypercholesterolaemic Obese Asian Subjects.” Singapore Medical Journal 42 (2001): 6-10.

Lehtimaki, T., et al. “Microcrystalline Chitosan Is Ineffective to Decrease Plasma Lipids in Both Apolipoprotein E Epsilon4 Carriers and Non-carriers: A Long-term Placebo-Controlled Trial in Hypercholesterolaemic Volunteers.” Basic and Clinical Pharmacology and Toxicology 97 (2005): 98-103.

Metso, S., et al. “The Effect of Long-term Microcrystalline Chitosan Therapy on Plasma Lipids and Glucose Concentrations in Subjects with Increased Plasma Total Cholesterol.” European Journal of Clinical Pharmacology 59, no. 10 (2003): 721-726.

Mhurchu, C. N., et al. “The Effect of the Dietary Supplement, Chitosan, on Body Weight: A Randomised Controlled Trial in 250 Overweight and Obese Adults.” International Journal of Obesity and Related Metabolic Disorders 28 (2004): 1149-1156.

Schiller, R. N., et al. “A Randomized, Double-Blind, Placebo-Controlled Study Examining the Effects of a Rapidly Soluble Chitosan Dietary Supplement on Weight Loss and Body Composition in Overweight and Mildly Obese Individuals.” Journal of the American Nutraceutical Association 4 (2001): 42-49.