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. 1 In turn, this appears to lead to a risk of osteoporosis in adults and growth retardation 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. 2 Finally, there has been a case report of arsenic poisoning caused by long-term use of chitosan supplements. 3 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.
