Iodine Bioavailability and Accumulation of Arsenic and Cadmium in Rats Fed Sugar Kelp (Saccharina latissima)

In Vivo Bioavailability and In Vitro Bioaccessibility of Iodine in Edible Seaweeds: Method Development and Health Implications

Both iodine (I) deficiency and I excess can adversely affect human health. Seaweed consumption is one of the most important natural sources for I. This study assessed I relative bioavailability (RBA) in seaweed using an in vivo mouse model and compared it with I bioaccessibility measured by three in vitro methods (Physiologically Based Extraction Test (PBET), the Solubility Bioaccessibility Research Consortium (SBRC), and the Unified Bioaccessibility Research Group of Europe Method (UBM)). Total I concentrations in 26 seaweed samples from four species ranged from 52.4 to 1322 mg/kg of dry weight. The I RBA varied from 18.5% to 89.0%, significantly influenced by inorganic I percentage (r = 0.50, p < 0.01) and total dietary fiber contents (r = -0.28, p < 0.05) in seaweeds. The I bioaccessibility varied among species and methods and were affected by the pH of gastric solution, as well as the structural changes in seaweed during in vitro extraction. Correlation analysis demonstrated that PBET was the best predictor for I RBA (R2 = 0.64). These results developed an appropriate in vitro method for predicting I bioavailability in seaweeds, which is highly beneficial for the accurate assessment for I dietary intake.

Cadmium bioavailability in market nori and kelp: A comparison with rice and mechanisms underlying reduction in rice cadmium bioavailability with nori and kelp consumption

Seaweeds, despite being rich in beneficial substances, also contain toxic metals such as cadmium (Cd), leading to ongoing debates about their health impacts. This study assessed the risk of Cd exposure from consuming nori and kelp, as well as the potential benefits of these seaweeds in mitigating Cd exposure from rice, using mouse bioassays. The results indicated that all test nori samples (n = 35) had Cd concentration exceeding 1.2 μg g-1, while the majority of kelp samples (18 out of 24) contained <0.5 μg g-1. When mixed with Cd-free rice at a 5 % (w/w) ratio and administered to mice for 14 days, kelp samples with 0.36 and 0.50 μg g-1 Cd (Kelp-0.36 and Kelp-0.50) did not result in Cd accumulation in the liver or kidneys. Conversely, nori samples with 1.30 and 1.67 μg g-1 Cd (Nori-1.30 and Nori-1.67) led to significant Cd accumulation, highlighting the exposure risk associated with nori. This risk was further emphasized by a doubling of Cd accumulation in the tissues of mice fed sushi containing nori compared to those fed sushi without nori. However, the Cd accumulation from consuming Nori-1.30 and Nori-1.67 was comparable to that from rice with a lower Cd concentration (0.93 μg g-1), suggesting a lower bioavailability of Cd in nori than in rice. More promisingly, when consumed with Cd-containing rice at a 5 % (w/w) ratio, Kelp-0.36, Kelp-0.50, Nori-1.30, and Nori-1.67 reduced the accumulation of rice Cd in mouse tissues by 25.8 %-48.1 %, primarily by increasing the relative abundances of Bacteroides in the gut of mice and enhancing fecal output, which in turn increased the excretion of rice-derived Cd by 1.46-1.54 times. These findings suggest that kelp consumption may be relatively safe, while caution is advised for nori. Moreover, regular consumption of specific amounts of seaweeds, particularly kelp, could help to reduce Cd exposure from rice.

Evaluation of the Bioavailability of Iodine and Arsenic in Raw and Cooked Saccharina japonica Based on Simulated Digestion/Caco-2 Cell Model

Kelp is a traditional healthy food due to its high nutritional content; however, its relatively high contents of iodine and arsenic have raised concerns about its edible safety. This study explored the effects of different cooking treatments on the contents of iodine and arsenic in kelp, evaluated the bioaccessibility and bioavailability of iodine and arsenic in kelp using in vitro digestion, and compared the differences in the transport characteristics of iodine in kelp and KIO3 using a Caco-2 monolayer cell transport model. The results show that the content of target elements that reached systemic circulation could be reduced by cooking and gastrointestinal digestion. The highest reductions in iodine and arsenic were 94.4% and 74.7%, respectively, which were achieved by boiling for 10 min. The bioaccessibility and bioavailability of iodine and arsenic were significantly improved by a cooking treatment. However, the contents of iodine and arsenic decreased significantly, with the bioaccessibility of iodine reducing from 3188.2 μg/L to 317.0 μg/L and that of arsenic reducing from 32.5 μg/L to 18.1 μg/L in the gastric phase after boiling. The findings also show that the efficiency of iodine transport in kelp and KIO3 was positively correlated with the transport time and negatively correlated with the concentration of iodine. With the increase in the iodine concentration, the rate of iodine transport in kelp decreased from 63.93% to 3.14%, but that of KIO3 was stable at around 35%, which indicates that the absorption efficiency of iodine from kelp was limited, even when too much kelp was ingested. In conclusion, the edible safety of kelp is significantly improved after cooking. The risk of excessive iodine and arsenic intake caused by consuming kelp is extremely low, and as an effective iodine supplement source, kelp has higher edible safety compared with KIO3. This study clarifies the safety of algae based on iodine and arsenic contents and also provides a basis for the formulation of food safety standards.

Simultaneous speciation analysis of arsenic and iodine in human urine by high performance liquid chromatography-inductively coupled plasma mass spectrometry

A high-performance liquid chromatography-inductively coupled plasma mass spectrometry-based method was developed for the simultaneous determination of four iodine species (i.e. iodate, 3-iodo-tyrosine, 3,5-diiodo-tyrosine, and iodide) and six arsenic species (i.e. arsenobetaine, arsenite, dimethylarsinic acid, arsenocholine, methylarsonic acid, and arsenate) in human urine. The chromatographic separation was performed on a Dionex IonPac As7 anion exchange column. The mobile phase was initiated with 0.5 mmol/L ammonium carbonate solution, followed by 50 mmol/L ammonium carbonate/100 mmol/L ammonium nitrate solution (with 4% methanol). The limits of quantification of the analytes ranged from 0.045 to 2.26 μg/L. At three spiked levels (10.0, 20.0, 50.0 μg/L), the average recoveries (%) ranged from 87.4 to 113.1%, and the relative standard deviations (RSD, %) ranged from 0.4 to 17.2%. The ratio of the sum of six arsenic species to the total arsenic measured by ICPMS ranged from 77.4 to 121.2%, and the ratio of the sum of the four iodine species to the total iodine ranged from 70.7 to 114.7%, indicating a good agreement between these two methods for both arsenic and iodine.

Bioavailability of iodine from a meal consisting of sushi and a wakame seaweed salad-A randomized crossover trial

The consumption of seaweed is on the rise in the Western world. Seaweeds may contain substantial amounts of iodine, and some species could serve as a potential dietary iodine source. However, limited data on the iodine content and in vivo bioavailability of iodine from seaweeds exist. The objective was to assess whether iodine from a meal consisting of sushi with nori, (Porphyra spp) and a wakame seaweed salad (Undaria pinnatifida) had similar bioavailability as a potassium iodide reference supplement of similar iodine content. A randomized 2 × 2 crossover trial (AB/BA model) was conducted in 20 healthy young women. One intervention arm consisted of a meal with sushi and wakame salad (231 μg iodine), and the other of potassium iodide (KI) supplement (225 μg iodine). Urinary iodine concentration (UIC) was measured at 11 different time points for 48 h after the interventions. The UIC increased after consumption of both the sushi and wakame meal and the KI supplement, but the median UIC was higher after ingestion of the KI supplement. The estimated bioavailability of iodine during the first 24 h was 75% from sushi with wakame and 97% from the KI supplement. The bioequivalence analyses confirmed that the KI supplement had higher estimated bioavailability than the sushi and wakame meal, however, with small margins. Our findings on iodine bioavailability imply that sushi and wakame could be potential iodine sources in the diet, which may be favorable for population groups at risk for iodine deficiency. However, further research is needed to account for the variability of iodine content in seaweeds by different locations and degree of processing, to assure that the iodine levels are stable and predictable for the consumers.