IngredientsHizikia fusiformis (Harvey) Okamura, commonly known as "hijiki seaweed" (syn. Sargassum fusiforme (Harvey) Setchell), is an edible brown alga belonging to the class Phaeophyceae, order Fucales, and family Sargassaceae. The two names β Hizikia fusiformis and Sargassum fusiforme β are in current use in the scientific literature; the latter is the more recently accepted nomenclature but both appear widely in peer-reviewed journals.
The Japanese name is written γγΈγ or using the kanji ιΉΏε°Ύθ / ηΎζ θ; it is sometimes spelled hiziki or, in Korean, tot (ν³). It is a brown seaweed that grows wild on the rocky coastlines of East Asia. In Chinese it is known as Yangqicai (ηΎζ θ). Its first recorded use as a traditional Chinese medicinal plant appears in the Shennong Bencao Jing, dated approximately 200 AD, where it was referred to as Haizao (seaweed) and described as a treatment for tumor-like induration, dysuria, and edema.
H. fusiformis grows naturally on lower intertidal rocks around the coastline of the northwest Pacific Ocean and is widely used as a food delicacy, marine vegetable, and medicinal herb in China, Korea, Japan, and Southeast Asia. Within Japan specifically, hijiki (Sargassum fusiforme) grows in rocky areas from southern HokkaidΕ to the southern tip of Kyushu; it is in season from March to May. Although hijiki has been consumed since ancient times, domestic production has been declining, and now nearly 90% of hijiki sold in Japan comes from South Korea and China.
Hijiki seaweed (γ²γγ in Japanese) is frequently sold in stores in its dried form and must be rehydrated and then cooked before eating. The small, soft buds are called mehijiki, and the long, chewy stems are called nagahijiki. Hijiki typically comes in a twig-like dried form or as small buds resembling dry black tea; both forms are black in color and swell approximately three to five times their dry size once cooked or rehydrated.
After harvesting, hijiki is dried in the sun, then washed and steamed; in some regions it is steamed or boiled in its raw state, with the buds removed from the stems during this process and sold separately as nagahijiki (stems) and mehijiki (buds). The Ise and Boshu methods are the two main traditional harvesting techniques; the more common Ise method involves sun-drying the hijiki at the harvest site, then transporting it to a processing site for cleaning, steaming, and final drying. Beyond whole dried seaweed, hijiki is available as extracts and, in cosmetics, as a heat-treated or fermented extract.
Hijiki is usually dried for preservation and then reconstituted in water before cooking; it is used in simmered dishes, mixed with rice, and in salads, among others. Hijiki has a nutty flavor and a firm texture and is typically used as a soy sauce-simmered condiment along with a breakfast serving and as a topping on steamed rice.
Hijiki has been a part of the Japanese culinary sphere and diet for centuries. It is thought to have been consumed since the Yayoi era (approximately 100β200 AD), with material believed to be hijiki found in pottery at Ryugado Cave in Kochi prefecture. The word first appeared in the literary work Tales of Ise, published during the early Heian period (around 880 AD), where the poet Ariwara no Narihira references sending hijiki to his lover. By the 17th century, a cooking book published in 1643β1644 AD describes stir-fried and marinated preparations of hijiki.
In the Edo era, with the development of traffic networks, hijiki was distributed around the country alongside kelp, laver, wakame, and other seaweed products. Kombu, nori, hijiki, and wakame are also among the foods offered to the gods as part of Shinto religious practices.
In traditional Japanese folk medicine, hijiki was valued as a tonic for promoting overall health and longevity; it was believed to support hair growth, contributing to the saying "eating hijiki will give you beautiful, black hair," and was prescribed to strengthen bones and teeth due to its high calcium content. Hijiki was also used to address digestive issues including constipation, owing to its rich dietary fiber, while its mineral-rich profile β especially iodine, iron, and magnesium β made it a popular remedy for fatigue, anemia, and thyroid imbalances.
In Chinese herbal medicine, hijiki was sometimes combined with other seaweeds like kombu and wakame to enhance its effects in purifying the blood, regulating fluid balance, and detoxifying the body. Its earliest documented medicinal role in China is in the Shennong Bencao Jing (dated ~200 AD), where it was renowned for treating tumor-like induration, dysuria, and edema.
H. fusiformis is widely used as a food delicacy, marine vegetable, and medicinal herb in China, Korea, Japan, and Southeast Asia. In Korea it is known as tot, and the seaweed has been cultivated there; at present, H. fusiformis has been effectively cultivated in southern China and Korea, with South Korea producing 28,157 tons dry weight per hectare per year as of 2015.
In English-language publishing, the word "hijiki" first appeared in 1867 in A Japanese and English Dictionary by James C. Hepburn. Starting in the 1960s the word came into wide use in the United States, with the product (imported in dried form from Japan) becoming widely available at natural food stores.
Sargassum fusiforme polysaccharides (SFPs) are acidic polysaccharides that possess significant medicinal and commercial potential; the primary constituents are alginic acid (alginate), fucoidan, and laminaran. Wang et al. (2009) reported that wild S. fusiforme contained 32.18% alginic acid (calculated as glucuronic acid), 2.40% fucoidan (calculated as fucose), and 0.54% laminarin (calculated as glucose).
Fucoidan is the most studied single compound. It is a sulfated polysaccharide known for its potential antioxidant, anti-inflammatory, and anti-cancer properties. Fucoidans from Hizikia fusiforme are characterized by high molecular weights β up to 950 kDa in native form β and their sulfate ester groups impart a negative charge on the macromolecule skeleton, giving fucoidans their anionic character.
A comparative study of two S. fusiforme strains found that, compared with several other algae, S. fusiforme can be recommended as a nutritious food for its high levels of minerals, polyunsaturated fatty acids, phlorotannins, fucoidan, and alginate. The alginate content ranged from 14.97β26.30% across the two strains, while fucoidan content ranged from 5.30β11.60%.
Several compounds have been isolated from brown seaweeds including phlorotannins, fucoxanthin, fucoidan, alginate, and laminarin β almost all of which have been found to possess various biological activities. Phlorotannins, members of the polyphenolic group of secondary metabolites, have been found in abundance in brown algae belonging to the Fucaceae, Sargassaceae, and Alariaceae families. In S. fusiforme, phlorotannin content has been measured at 17.55β48.91 mg/g in one strain.
Fucoxanthin is a compound belonging to the group of carotenoids and is considered one of the most abundant and characteristic pigments of brown algae; edible algae that contain fucoxanthin include those of the genus Hijikia (and related genera such as Undaria, Sargassum, and Laminaria).
Hijiki seaweed contains potassium, calcium, and magnesium. Hijiki also contains beta-carotene, which promotes healthy skin and mucous membranes, and is rich in iodine, which helps regulate thyroid gland functioning and basal metabolism. As a food source, Sargassum is high in protein and low in fat, and it is rich in polysaccharides, dietary fiber, vitamins, minerals, amino acids, and a variety of trace elements.
A distinguishing and safety-relevant constituent is inorganic arsenic (arsenate). Total arsenic in hijiki has been measured at concentrations ranging from 18 to 124 mg/kg. Inorganic arsenic β which can cause liver cancer β was detected in hijiki samples at concentrations in the range of 67β96 mg/kg as sold, while other types of seaweed were all found to contain less than 0.3 mg/kg inorganic arsenic (the detection limit of the method used).
Modern medical research has demonstrated that S. fusiforme possesses antioxidant, anti-tumor, and anti-inflammatory properties, as well as the ability to regulate blood sugar and enhance human immunity. Fucoidan from H. fusiforme has been shown to act through multiple antioxidant pathways: a fucoidan fraction (SFF-PS-F5, molecular weight 213.33 kDa) obtained after fermentation of S. fusiforme with Lactobacillus rhamnosus, when tested in vitro on Vero cells damaged by hydrogen peroxide stimulation, suppressed apoptosis by scavenging intracellular reactive oxygen species and up-regulating intracellular antioxidants.
Fucoidan is a naturally derived compound found in brown algae that has gained attention for its anticancer properties, although the exact mechanism of action is currently not fully established. The general bioactivity of fucoidan is difficult to establish due to species-related structural diversity, growth conditions, and extraction method. The main pathways influenced by fucoidan are the PI3K/AKT pathway, the MAPK pathway, and the caspase pathway. PTEN appears to be important in the fucoidan-mediated effect on the AKT pathway, and interactions with VEGF, BMP, TGF-Ξ², and estrogen receptors are also implicated.
Several studies have reported that ethanol extracts of H. fusiformis, fucoidan, and alginate isolated from H. fusiformis possess anti-apoptotic effects in relevant model systems.
Fucoidan with a molecular weight of 102.67 kDa isolated from Hizikia fusiforme was found to possess strong antioxidant activity; studies of its anti-photoaging effect in UVB-irradiated human keratinocytes (HaCaT cells) showed that fucoidan effectively reduced intracellular reactive oxygen species levels and improved cell viability, while also significantly decreasing UVB-induced apoptosis by regulating the protein expression of Bax, Bcl-xL, PARP, and Caspase-3 in a concentration-dependent manner.
Phlorotannins exert an antibacterial and anti-inflammatory effect by suppressing oxidative phosphorylation, altering target cell membrane permeability, and triggering cell death by interacting with target microbial proteins; the phenolic aromatic ring and hydroxyl groups of various phlorotannins have been shown to bind to microbial proteins and induce cell lysis.
Important note: As detailed in the 2021 systematic review published in Foods (PMC8306711), the overwhelming majority of pharmacological studies on H. fusiformis are in vitro (cell culture) or in vivo (animal) studies. As of the review's coverage period (2010β2021), there are no published human clinical trials examining hijiki as a therapeutic agent. All evidence for pharmacological effects must therefore be characterized as preliminary.
Between 2010 and 2021, anticancer and antitumor activity accounted for 15.09% of published pharmacological research articles on H. fusiformis. The evidence is exclusively preclinical. One study investigated the antiproliferative effects of fucoidan from three regional hijiki (Hizikia fusiforme) samples from Zhejiang (China), Jeju (Korea), and Wando (Korea); hijiki was processed using 1% citric acid to decrease heavy metal content. The most active fucoidan fraction (JHCF4) showed the highest fucose and sulfate content and decreased Hep3B (human hepatocellular carcinoma) cell growth in 48 hours with a half-maximal inhibitory concentration (IC50) of 33.53 Β± 2.50 ΞΌg/ml; nuclear staining demonstrated that the anticancer activity involved apoptosis.
Polysaccharides from S. fusiforme have demonstrated valuable in vivo anti-cancer and immunomodulatory effects in animal studies. In one study, the polysaccharide fraction of S. fusiforme was purified and selenylated; the selenylated polysaccharide was administered intraperitoneally for 10 days at three dose levels (50, 100, and 150 mg/kg) in mice bearing S180 (murine sarcoma) cancer cells, and antioxidant activity was assessed. These studies are animal models and cannot be extrapolated to humans.
Antioxidant activity accounted for 15.09% of pharmacological publications on H. fusiformis between 2010 and 2021. A study used optimized microwave-assisted extraction and achieved maximum antioxidant activities measured as DPPH radical inhibition (28.01%), ABTS inhibition (36.07%), total phenolic content (43.65 mg GAE/g), and total flavonoid content (17.67 mg CAE/g) under specific extraction conditions. These are in vitro assay results; clinical significance in humans is not established.
Anti-inflammatory research accounted for 11.32% of pharmacological publications on H. fusiformis from 2010 to 2021. Evidence is confined to in vitro and animal studies. Fucoidan and phlorotannins are the most studied anti-inflammatory constituents; their mechanisms in cell models are described in Section 4 above. No human clinical data are available.
Antidiabetic properties accounted for 9.43% of pharmacological publications on H. fusiformis between 2010 and 2021. A study in C57BL/6J male mice fed a high-fat diet for 4 weeks developed severe hypoglycemia; five polysaccharides prepared from S. fusiforme were tested, and four of them (Sf-2, Sf-3, Sf-3-1, and Sf-A) significantly prevented early fasting hypoglycemia without inducing hyperglycemia. Additionally, Sf-1 and Sf-A could significantly prevent HFD-induced weight gain, while the SFPs mainly attenuated the HFD-induced decrease in Bacteroidetes and had considerable influence on the relative abundance of Oscillospira, Mucispirillum, and Clostridiales. This research is animal-based; no human clinical trials exist.
Studies have investigated neuroprotective properties of H. fusiformis extracts. Reviews have outlined antioxidant and neuroprotective effects of S. fusiforme. Evidence remains at the level of in vitro cell and animal studies; no human data exist for this indication.
Photoprotective research accounted for 11.32% of pharmacological publications on H. fusiformis between 2010 and 2021. The most developed line of evidence concerns fucoidan's activity in UVB-exposed keratinocyte cell lines (see Section 4). Currently, few drugs are available that protect from UV radiation-induced damage, which frequently causes skin cancer; the photoprotective effects of hijiki-derived compounds are an active area of research. All evidence is preclinical.
Osteoprotective activity accounted for 7.55% of pharmacological publications on H. fusiformis between 2010 and 2021. Mechanistic studies have examined polysaccharide fractions in cell and animal models; no controlled human studies have been conducted.
Polysaccharides from S. fusiforme have demonstrated immunomodulatory effects in animal studies. Biological activities studied for S. fusiforme polysaccharides include antioxidant, antitumor, immunomodulatory, antiviral, intestinal flora-regulating, and anti-diabetic properties. All available evidence is from in vitro and animal studies.
Research on intestinal homeostasis in conjunction with gut microbiota composition has become a hotspot in S. fusiforme research. Animal experiments have shown that polysaccharides of S. fusiforme significantly prevented diet-induced hypoglycemia in mice while modifying gut microbiota composition. As with other pharmacological areas, human evidence is absent.
Antibacterial properties accounted for 3.77% of pharmacological publications on H. fusiformis between 2010 and 2021. Evidence is restricted to in vitro antimicrobial assays.
A 2021 systematic review found an increase in publications over the preceding decade but concluded that further studies and strategies are required to develop H. fusiformis as a promising resource for the nutrition and pharmacological industries. No area of hijiki's pharmacological use is supported by human clinical trial evidence. All biological activity findings to date are from in vitro cell culture studies or in vivo animal experiments and must be treated as preliminary and hypothesis-generating.
Over the last decade, research has focused on the antioxidant, anticancer, antitumor, anti-inflammatory, photoprotective, neuroprotective, antidiabetic, immunomodulatory, osteoprotective, and gastroprotective properties of H. fusiformis extracts. These correspond to the following body systems:
There are no standardized clinical dosages for hijiki as a dietary supplement because no human clinical trials have established therapeutic dosing. Dosages reported in preclinical research are as follows:
In the context of dietary consumption, the Ministry of Health, Labour and Welfare of Japan reported that the average daily consumption of hijiki for Japanese people is estimated at 0.9 g, and that consuming more than 4.7 g hijiki per day could result in an intake of inorganic arsenic exceeding the tolerable daily intake.
Several government food safety agencies advise consumers to avoid consumption of hijiki seaweed. Testing has shown that it contains significantly higher concentrations of inorganic arsenic than other types of seaweed, and these results have been independently verified.
In 2004, the UK Food Standards Agency (FSA) issued a warning not to eat hijiki; this alert was reissued in 2010. The European Commission also discussed further action following the risk alert. Based on health risk information received from Health Canada, the Canadian Food Inspection Agency (CFIA) advises consumers to avoid consumption of hijiki seaweed, as test results have indicated that levels of inorganic arsenic are significantly higher than in other types of seaweed.
Although no known illnesses have been specifically associated with consuming hijiki seaweed to date, inorganic arsenic has been identified as carcinogenic to humans; exposure to inorganic arsenic has been linked with gastrointestinal effects, anemia, and liver damage.
Feeding rats a 3% hijiki diet led to a marked accumulation of arsenic in blood and tissues, and evoked a high body temperature and abnormal blood biochemistry including elevated plasma alkaline phosphatase activity and inorganic phosphorus, consistent with arsenic poisoning.
A study of 104 children and 101 pregnant women in Japan found that total and inorganic arsenic intake were higher among frequent consumers of hijiki seaweed in both groups; results indicated that hijiki consumption elevates inorganic arsenic intake in populations sensitive to environmental contaminants.
People who follow a macrobiotic diet that often includes large amounts of seaweed may be at greater risk.
The Japanese Ministry of Agriculture, Forestry and Fisheries advises that rehydrating dried hijiki in water and rinsing it reduces the amount of arsenic by roughly 50%; boiling and draining reduces that amount by approximately 90%.
To remove inorganic arsenic from the seaweed, boiling in seawater three or four times can remove 86β92% of total arsenic; after this procedure, total arsenic in the dried seaweed has been measured at 8.6β18.6 mg/kg and arsenic acid at 0.6β0.9 mg As/kg.
A combination treatment of heating in water to 90Β°C followed by soaking in 2% NaCl solution removed up to 92% of the inorganic arsenic, making it safer for human consumption. Repeating parboiling for 5 minutes twice has been shown to achieve a 79% reduction of inorganic arsenic in hijiki.
One study also found that none of the other varieties of seaweed tested contained detectable levels of inorganic arsenic, indicating that seaweeds other than hijiki are safe to eat with respect to their arsenic content.
The Korean Food and Drug Administration (KFDA) has established a maximum contaminant level of inorganic arsenic in hijiki-based food of 1 mg/kg, while the maximum limits in China and Australia are 1.5 mg/kg and 1 mg/kg, respectively.
Hijiki is rich in iodine, which helps regulate thyroid gland functioning and basal metabolism; however, excessive intake can lead to a decrease in thyroid function. This is relevant both for individuals with thyroid disorders and for those following diets heavy in seaweed consumption.
The general bioactivity of fucoidan is difficult to establish due to factors such as species-related structural diversity, growth conditions, and the extraction method. Different algae species, extraction methods, harvesting seasons, and growth regions lead to structural variation of fucoidan, which would affect its bioactivities. This variability poses a challenge for standardization of any hijiki-derived supplement.
Health conditions that Hijiki may help support.
Body systems that Hijiki may help support.
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