The aim of this study was to examine the absorption of fucoidan through the intestinal tract. Fucoidan (0.1, 0.5, 1.0, 1.5 and 2.0 mg/mL) was added to Transwell inserts containing Caco-2 cells. The transport of fucoidan across Caco-2 cells increased in a dose-dependent manner up to 1.0 mg/mL. It reached a maximum after 1 h and then rapidly decreased. In another experiment, rats were fed standard chow containing 2% fucoidan for one or two weeks. Immunohistochemical staining revealed that fucoidan accumulated in jejunal epithelial cells, mononuclear cells in the jejunal lamina propria and sinusoidal non-parenchymal cells in the liver. Since we previously speculated that nitrosamine may enhance the intestinal absorption of fucoidan, its absorption was estimated in rats administered N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in their drinking water. Rats were fed 0.2% fucoidan chow (BBN + 0.2% fucoidan rats), 2% fucoidan chow (BBN + 2% fucoidan rats) and standard chow for eight weeks. The uptake of fucoidan through the intestinal tract seemed to be low, but was measurable by our ELISA method. Fucoidan-positive cells were abundant in the small intestinal mucosa of BBN + 2% fucoidan rats. Most fucoidan-positive cells also stained positive for ED1, suggesting that fucoidan was incorporated into intestinal macrophages. The uptake of fucoidan by Kupffer cells was observed in the livers of BBN + 2% fucoidan rats. In conclusion, the absorption of fucoidan through the small intestine was demonstrated both in vivo and in vitro.

We performed an oral administration study of fucoidan in 396 Japanese volunteers and investigated significant factors concerning the absorption of fucoidan. Urine samples were collected at 0, 3, 6, and 9 h after ingestion of 3 g of fucoidan. Fucoidan was detected in urine after ingestion in 385 out of 396 subjects. The maximum value (mean ± standard deviation (SD)) of urinary fucoidan was 332.3 ± 357.6 μg/gCr in subjects living in Okinawa prefecture, compared with 240.1 ± 302.4 μg/gCr in subjects living outside Okinawa. Compared with the estimated urinary excretion of fucoidan by place of residence, those of subjects living in Okinawa prefecture were significantly higher than those living outside Okinawa prefecture (p < 0.01). In addition, subjects living in Okinawa prefecture consumed significantly greater amounts of mozuku compared with those living outside Okinawa prefecture (p < 0.01). Multiple regression analysis showed that having Okinawa prefecture as a place of residence was a significant factor (p < 0.01) contributing to the estimated urinary excretion of fucoidan. Because the habit of eating mozuku was significantly higher (p < 0.01) in subjects living in Okinawa prefecture than in those living outside Okinawa prefecture, the habit of eating mozuku was speculated to be a factor in the absorption of fucoidan.

Cancer survivors are highly motivated to seek information about the use of dietary supplements and complementary nutritional therapies to improve their quality of life. Fucoidan, a sulfated polysaccharide extracted from brown marine alga, exhibits a wide range of bioactivities, including anticancer activity. As natural killer (NK) cells serve an important role in defenses against tumor cells, the present study examined the effects of fucoidan extracted from Cladosiphon Okamuranus on NK cell activity in cancer survivors. A prospective, open‑label clinical study was conducted on cancer survivors treated with fucoidan via oral administration; 11 cancer survivors with a performance status of 0 or 1 participated and consumed 3 g of fucoidan for 6 months. No significant changes were observed in the mean activities of NK cells in total subjects following the ingestion of fucoidan. An analysis of each sex revealed that NK cell activity was significantly increased by the ingestion of fucoidan in male, yet not female subjects. Serum fucoidan levels were markedly increased following the ingestion of fucoidan and the peak levels ranged between 30 and 198 ng/ml. Tumor markers remained within the reference range during the trial period in subjects, in whom primary tumors were eradicated by treatment. The basal values of tumor markers were elevated in three cases; tumor markers were increased in two cases and decreased in one by the ingestion of fucoidan. These findings suggest that fucoidan enhances the activation of NK cells in male cancer survivors.