The Wikipedia article on carrageenan outlines a number of peer reviewed animal studies, the results of which are mixed with some researchers claiming carrageenan poses no health concerns, while others assert that it promotes gastrointestinal tract inflammation and increased incidence of tumours.
This study found no correlation between dietary carrageenan and tumour formation
- Cohen S and Ito N (2002) "A critical review of the toxicological effects of carrageenan and processed eucheuma seaweed on the gastrointestinal tract." Crit Rev in Toxicol 32(5) 413-444
Studies that found an increase in tumour formation:
Watanabe, K., Reddy, B. S., Wong, C. Q., & Weisburger, J. H. (1978). "Effect of dietary undegraded carrageenan on colon carcinogenesis in F344 rats treated with azoxymethane or methylnitrosourea" Cancer Research 38(12), 4427-4430.
Taché, S, Peiffer, G, Millet, A-S, and Corpet, DE. "Carrageenan gel and aberrant crypt foci in the colon of conventional and human flora-associated rats." Nutr Cancer 37:75–80, 2000.
Corpet, DE, Taché, S, and Préclaire, M. "Carrageenan given as a jelly, does not initiate, but promotes the growth of aberrant crypt foci in the rat colon" Cancer Lett 114:53–55, 1997b.
These studies show a link between GI inflammation and dietary carrageenan:
Bhattacharyya S, Dudeja PK and Tobacman JK (2010) "Tumor necrosis factor alpha-induced inflammation is increased but apoptosis is inhibited by common food additive carrageenan." Journal of Biological Chemistry 285(50): 39511-22
Borthakur A, Bhattacharyya S, Anbazhagan AN, Kumar A, Dudeja PK and Tobacman JK (2012) "Prolongation of carrageenan-induced inflammation in human colonic epithelial cells by activation of an NFκB-BCL10 loop." Biochimica and Biophysica Acta 1822(8): 1300-7