IngredientsDulse (Palmaria palmata), also called dillisk or dilsk (from Irish/Scottish Gaelic duileasc/duileasg), red dulse, sea lettuce flakes, or creathnach, is a red alga belonging to the division Rhodophyta, previously referred to as Rhodymenia palmata. The currently accepted scientific name for the species is Palmaria palmata (Linnaeus) Weber & Mohr 1805.
The current scientific name is rooted in the Latin word palma, meaning hand or palm of the hand, which is repeated in both parts of the name to emphasize the palm-like shape of the plant. The English common name "dulse" is the most widely employed in many languages. This vernacular name, as well as the alternative "dillisk," is closely related to "duileasc" (Gaelic) and "tellesk" (Breton). Other vernacular names include "creannach" (Gaelic), "søl" or "söl" (Norwegian/Danish and Icelandic), "goëmon à vache" (French, translated from the Breton "bezhin saout," meaning "cattle's seaweed"), and "botelho-comprido" (Portuguese).
It grows on the northern coasts of the Atlantic and Pacific Oceans. The fronds are variable in shape and colour, from deep rose to reddish purple, and are rather leathery in texture. The flat foliose blade gradually expands and divides into broad segments ranging in size to 50 centimetres long and 3–8 cm in width, which can bear flat, wedge-shaped proliferations from the edge. A closely related species, Palmaria mollis, is found in the Pacific, where it is known as Pacific dulse or red ribbon.
Dulse thrives in the subtidal and lower intertidal zones, anchoring to rocky substrates at depths of 0–20 meters in waters between 5–15°C. The erect frond of dulse grows attached by its discoid holdfast and a short inconspicuous stipe epiphytically onto the stipe of Laminaria or onto rocks.
Dulse is a very versatile ingredient; it can be eaten raw, having a salty flavour and chewy texture. It can also be dried and consumed as a snack or added to broths and stews to enhance flavour and act as a thickener. It can be boiled for several hours into a pulp with a porridge-like consistency. Other culinary uses include grinding the dried seaweed into a powder to be utilized as a garnish, or frying it into crispy chips; it is also used to complement seafood, vegetables, grain dishes, and can even be baked in breads and muffins.
Raw dulse offers mild salt, faint smoke, and dried-fruit sweetness. Toasting unlocks a bacon-like aroma without animal fat. Dulse flakes give chew; dulse powder vanishes into sauces, colouring them sunset red while adding plant umami.
The first written record of Europeans eating dulse dates to about 563 AD. A poem attributed to St. Columba refers to the monks of Iona, a small island off the western coast of Scotland, collecting dulse off the rocks for food. Fifth-century laws of archaic Ireland existed concerning the eating of duileasc.
Dulse has been harvested and consumed for over 1,000 years in the coastal communities of Ireland, Scotland, Iceland, and Maritime Canada, where it was eaten raw, dried, or roasted as a snack and used to flavour stews and breads, providing an important source of protein, iodine, and vitamins in subsistence diets. In Irish Gaelic tradition, dulse (known as dillisk or creathnach) was traded at coastal markets and fairs and was specifically noted for its energising and restorative properties among fishermen and labourers who chewed it dried during long working days.
It has an association with poverty, as it became a dietary supplement for Scots displaced to the coast in the 19th and 20th centuries, and was eaten as nourishment during the Great Famine in Ireland. Dulse was popular in Scotland right up through the 1800s, as observed by Charles Dickens in 1858 when he reminisces about the "dulse wives" selling dulse in Aberdeen.
A tradition in Northern Ireland is to eat dulse at the Ould Lammas Fair in County Antrim at the end of August. The festival marks the end of summer and has been going on since the 17th century. Along the Ulster coastline from County Down to County Donegal in the Republic of Ireland, it is eaten dried and uncooked as a snack.
In Iceland, where it is known as söl, it has been an important source of dietary fibre throughout the centuries. According to the Icelandic sagas dating back to 961 AD, söl (the Old Norse word for dulse) was a highly valued food source. Dulse makes its first appearance in Icelandic legal documents in 1150 AD, which state that it is "perfectly legal to collect and eat another man's dulse when traveling across his property."
Irish and Scottish immigrants brought their special love of dulse to the new world, especially to the hard-scrabble coasts of Maritime Canada, where a dulse tradition thrives to this day. Most commercially harvested dulse comes from the Bay of Fundy in New Brunswick, Canada, or from the western coast of Ireland.
In Irish and Scottish folklore, dulse was often mentioned as a powerful remedy for various ailments. It was believed to have healing properties, particularly for digestive issues and thyroid health, due to its high iodine content. During the seventeenth century, British sailors ate dulse to prevent scurvy, although it was originally used as an alternative to chewing tobacco. Dulse contains iodine, which prevents goitre — a connection recognized by traditional coastal communities long before the science of endocrinology.
Dulse is a potentially good source of proteins, ranging from 10–26% of dry mass. Its protein content, amino acid composition, and protein digestibility show significant seasonal variation: the highest protein content (21.9 ± 3.5%) is found in the winter–spring period and the lowest (11.9 ± 2.0%) in the summer–early autumn period. Most of the essential amino acids are present throughout the year.
Dulse contains high proportions of polysaccharides (38–74%), such as carrageenan, and a large variety of minerals (12–37%), such as iodine, potassium, sodium, calcium, magnesium, and iron. Despite a low proportion of lipids (0.2–3.8%), dulse can contain liposoluble vitamins such as β-carotene (provitamin A) and tocopherol (vitamin E), as well as omega-3 fatty acids.
Dulse provides a dense mineral and vitamin profile, reflected in its ash content, which typically ranges from 12–37%. Major minerals include potassium, chloride, magnesium, calcium, phosphorus, sodium, and sulphur.
After 6-hour in vitro digestion using porcine pepsin and porcine pancreatin, the digestibility of proteins from Palmaria palmata crude powder was estimated at 29.52 ± 1.47%. Relative digestibility was 56%, using casein hydrolysis as a 100% reference. The digestibility of Palmaria palmata proteins appears to be limited by the alga's non-proteic fraction. This is an important consideration when evaluating dulse as a protein supplement.
The major constituents of dulse proteins are phycobiliproteins, specifically phycoerythrin and phycocyanin. The proteins extracted from dulse are mainly composed of phycoerythrin (PE), followed by phycocyanin (PC) and allophycocyanin (APC). These pigment proteins are responsible for dulse's characteristic reddish colour and have been the subject of substantial bioactivity research.
In addition to their thickening and gelling properties, macroalgal sulphated polysaccharides can be characterized by biological activities such as antiviral ones. These polysaccharides form a major part of dulse's carbohydrate fraction and contribute to its viscosity and fibre content, which has implications for digestive and cardiovascular health research.
The presence of polyphenols, sulfated polysaccharides, vitamins, and other bioactive molecules contributes significantly to the antioxidant activity of dulse. Dulse is a rich source of bioactive compounds, including polysaccharides, antioxidants, minerals, and essential nutrients such as fatty acids, amino acids, and vitamins, making it a valuable functional ingredient.
Dulse's use to support the thyroid gland is primarily based on its high iodine content, as iodine is an essential nutrient required for the synthesis of thyroid hormones (thyroxine/T4 and triiodothyronine/T3). Historically, seaweeds like dulse have been used as natural dietary sources of iodine, particularly in populations with limited access to iodized salt or other iodine-rich foods.
Dulse contains the neurotoxic amino acid kainic acid, with levels ranging from trace amounts to approximately 560 µg/g dry weight. Concentrations of kainic acid in dulse can vary from below the limit of detection to concentrations exceeding 10,000 mg/kg dry weight. Cultivation of P. palmata for human consumption with very low levels of kainic acid can occur; however, research has reported that human safety standards for this compound have yet to be established.
Nine ACE-inhibitory peptides (YRD, AGGEY, VYRT, VDHY, IKGHY, LKNPG, LDY, LRY, FEQDWAS) have been isolated from dulse protein hydrolysates by reversed-phase HPLC, and the synthetic peptide LRY (IC50: 0.044 μmol) has been shown to have remarkably high ACE-inhibitory activity. Peptides derived from proteins and proteins involved in photosynthesis have demonstrated antioxidant and angiotensin-converting enzyme (ACE) inhibition activities.
Dulse contains polyphenols, sulphated polysaccharides, R-phycoerythrin, and bioactive peptides that exert antioxidant activity via free-radical scavenging (DPPH• and ABTS+ inhibition). Despite compositional variability, all seaweeds possess exceptional antioxidant potential. Antioxidants in seaweeds, including chlorophylls, vitamins, and phenolic compounds, help prevent oxidative stress, which can damage DNA, proteins, and nucleic acids, leading to diseases like cancer and diabetes.
Phycobiliproteins and chlorophyll a were simultaneously extracted from lyophilized dulse leaves via water-extraction and subjected to thermolysin digestion to produce a thermolysin-digested water-extract (d-DWE). This d-DWE significantly reduced tumour necrosis factor-α, interleukin-6, and nitric oxide in LPS-stimulated murine macrophages (RAW 264.7 cells), and orally administered d-DWE mitigated acute inflammation in carrageenan-induced paw oedema in mice. A decapeptide derived from the phycoerythrin β-chain and chlorophyll a decomposition products showed anti-inflammatory activity; the anti-inflammatory activity appeared to be caused by phycobiliprotein and chlorophyll a decomposition products.
Angiotensin I converting enzyme (ACE) is physiologically important in the regulation of blood pressure, catalysing the production of angiotensin II and the destruction of bradykinin. Specific inhibitors of the enzyme have been recognised as effective antihypertensive drugs, but synthetic ACE inhibitors can cause many significant undesirable side effects. Natural safe compounds are therefore desirable for prevention of hypertension. The dulse proteins showed slight ACE-inhibitory activity, whereas the inhibitory activity was extremely enhanced by thermolysin hydrolysis. Recombinant phycoerythrin α- and β-subunit peptides showed high ACE-inhibitory activities (rPEα: 94.4%; rPEβ: 87.0%), confirming that the original proteins of dulse ACE-inhibitory peptides are phycobiliproteins.
Accumulating evidence from in vitro and animal studies suggests seaweed has antihyperlipidaemic, anti-inflammatory, and antioxidant properties, which may in part be attributed to the high content of soluble dietary fibre in seaweeds. The viscosity of seaweed fibres is suggested to mediate antihyperlipidaemic effects via the alteration of lipid/bile acid absorption kinetics to decrease low-density lipoprotein cholesterol (LDL).
Evidence level: In vitro and ex vivo; limited human data.
A 1-butanol soluble extract of dulse harvested from Canadian Maritime locations has exhibited hydroxyl and stable free-radical scavenging activity as well as inhibition of lipid peroxidation, attributed to the reducing activity and polyphenol content of the dulse extract. The extract from dulse with greater UV exposure exhibited higher reducing activity, reflecting a greater requirement for endogenous antioxidant protection. Both grades of dulse extract inhibited AAPH-induced lipid peroxidation but had no effect on AMVN-induced lipid peroxidation, demonstrating the aqueous nature of the antioxidants involved. Dulse extract inhibition of HeLa cell proliferation was dose-dependent over 0.5–5.0 mg/mL and maximal at 48 and 72-hour incubation, with the antiproliferative effects likely reflecting the bioactivity of the polyphenol content.
In vitro studies have demonstrated high cytotoxic activity against HeLa and HCT-116 colorectal cancer cells and measurable DPPH scavenging in ethanolic and screw-pressed juice fractions, though no human clinical trials have yet confirmed these effects in vivo. The antioxidant evidence for dulse therefore remains at the preclinical stage.
Evidence level: In vitro and animal studies; one small human ex vivo study.
Dulse is reported to contain anti-inflammatory and antioxidant compounds. A study evaluated the ability of a phenolic dulse extract (DULEXT) to modulate the lipopolysaccharide (LPS)-mediated activation of primary human neutrophils, noting that no previous study had investigated these effects in primary human neutrophils. Strategies to diminish neutrophil activation have the potential to prevent pathological states.
Evaluating the preventive effects of several doses of DULEXT on oxidative state in LPS-activated human neutrophils showed that the extract induced a dose-dependent decrease in intracellular reactive oxygen species (ROS) production. Similar effects were observed after quantifying myeloperoxidase (MPO) release in culture supernatants, with the extract depressing pro-oxidant enzyme concentration. There was a remarkable decrease at a dose of 50 µg/mL.
This study used primary human cells rather than whole human subjects, so while the model is human-derived, it does not constitute a clinical trial. Evidence for anti-inflammatory effects in living humans remains weak.
Evidence level: Preclinical animal studies; limited human RCT evidence with mixed results.
A study examined the resistance of a renin-inhibitory tridecapeptide IRLIIVLMPILMA derived from a Palmaria palmata papain hydrolysate during gastrointestinal transit. Following simulated GI digestion, breakdown products included the known renin and ACE-inhibitory dipeptide IR. In vivo animal studies using spontaneously hypertensive rats (SHRs) were used to confirm antihypertensive effects. After 24 hours, the SHR group fed the P. palmata protein hydrolysate recorded a drop of 34 mmHg in systolic blood pressure from 187 (±0.25) to 153 (±0.64) mmHg, while the group fed the tridecapeptide IRLIIVLMPLIMA presented a drop of 33 mmHg in blood pressure. This evidence comes from animal models only and has not been replicated in controlled human trials.
Regarding lipid metabolism, a study investigated the effects of P. palmata from northern Japan on lipid metabolism and glycaemic control in participants with hypercholesterolaemia. An 8-week, randomised, double-blind, placebo-controlled, parallel-group comparison trial was conducted, enrolling Japanese participants with serum LDL-C ≥120 mg/dL. The participants were randomly assigned to take either capsules containing P. palmata (2 g/day) or placebo capsules. The study did not show that P. palmata had a significant effect on serum LDL-C nor glycaemic control, but hypertriglyceridaemia could be ameliorated by administration of P. palmata in women.
A separate study examined the effect of a fibre extract: a total of 60 healthy participants (30 male and 30 female), aged 20 to 58 years, were assigned to consume the Palmaria palmata fibre extract (5 g/day), Synergy-1, and a placebo (maltodextrin) for a duration of 4 weeks with a minimum 4-week washout between each treatment in a double-blind, randomised crossover study conducted over 5 months. Supplementation for 4 weeks with Palmaria palmata resulted in favourable changes to lipid profiles with a reduced LDL:HDL ratio; however, intention-to-treat univariate ANCOVA identified no significant difference between the treatment groups.
Evidence level: One human RCT; results were contrary to the anticipated anti-inflammatory hypothesis.
Palmaria palmata is reported to contain anti-inflammatory and antioxidant compounds, but no study had investigated these effects in humans prior to this trial. A randomised parallel placebo-controlled human intervention study was carried out to investigate the effect of consuming P. palmata (5 g/day) incorporated into a bread on serum markers of inflammation (C-reactive protein and cytokine analysis), with secondary analysis investigating changes in lipids (cholesterol, triglycerides), thyroid function (TSH), and antioxidant status.
Consumption of P. palmata-enriched bread significantly increased serum CRP (+16.1%, p = 0.011), triglycerides (+31.9%, p = 0.001) and TSH (+17.2%, p = 0.017) compared to the control group. In vitro evaluation of P. palmata extracts and protein hydrolysates identified a significant induction of IL-8 secretion by Caco-2 cells, and the hot water P. palmata extract was shown to increase adipocyte glycerol release. The conclusion of this human study was that P. palmata stimulates inflammation, increases serum triglycerides, and alters thyroid function; however, these changes are not likely to impact health as changes remained within the normal clinical range. The in vitro data provided indications that IL-8 may contribute to the apparent immunostimulation noted in the human study.
This is a significant finding because it represents the only fully published randomised human intervention trial investigating dulse's effects on inflammation. Its results run counter to the popular characterisation of dulse as anti-inflammatory, and the study's limitations — including the delivery form (enriched bread) and population (healthy adults) — must be considered. The changes, though statistically significant, remained within normal clinical ranges, and effects in populations with pre-existing inflammatory conditions remain uninvestigated.
Evidence level: Mechanistically supported; no dedicated clinical trials on dulse and thyroid disease.
Dulse's use to support the thyroid gland is primarily based on its high iodine content. Iodine is an essential nutrient required for the synthesis of thyroid hormones (T4 and T3). Historically, seaweeds like dulse have been used as natural dietary sources of iodine, particularly in populations with limited access to iodized salt. Insufficient iodine intake can lead to thyroid dysfunction, such as goitre and hypothyroidism.
There are no dedicated clinical trials on dulse supplementation and thyroid disease outcomes. The 2016 Allsopp RCT noted an increase in TSH at a dose of 5 g/day, which warrants caution for individuals with pre-existing thyroid disorders.
Evidence level: In vitro only; one human RCT showed no significant effect.
Sulphated polysaccharides from dulse have shown alpha-glucosidase inhibitory activity in vitro, slowing carbohydrate digestion and potentially reducing postprandial glucose spikes, though this has not been validated in human subjects. The human RCT by Takase et al. (2020) at a dose of 2 g/day found no significant effect on glycaemic control parameters.
Dulse is available in several commercial forms: whole dried fronds, flakes, granules, powder, and encapsulated extract. The following doses have been reported specifically in published research:
There is no established standardised therapeutic dose for dulse in any pharmacopoeia or regulatory monograph. All clinical doses above are from individual studies and should not be taken as universal recommendations.
Seaweeds are a source of essential elements such as iodine; however, high intake levels of iodine can cause damage to human health. High intake levels of iodine can cause damage to human health. While modest intake supports thyroid hormone production, very high iodine can aggravate thyroid disorders in susceptible people (hyper- or hypothyroidism).
The 2016 human RCT found a statistically significant increase in TSH when consuming 5 g/day of dulse-enriched bread, though the change remained within the normal clinical range.
Dulse is an edible seaweed known to be very rich in potassium. A case of hyperkalemia precipitated by the consumption of dulse by a patient with known renal disease has been reported in the medical literature. Laboratory analysis in the reported case revealed a serum potassium level of 8.6 mmol/L (normal range 3.5 to 4.9 mmol/L). The only recent dietary change the patient could recount was consuming approximately 200 g of dulse within the preceding 24 hours. To the knowledge of the reporting physicians, this was the first published report of hyperkalemia due to dulse consumption. Dulse is high in potassium, with concentrations upwards of 34 times greater than that found in bananas.
Hyperkalemia is rare in individuals with normal renal function, regardless of dietary intake, due to the ability of the kidneys to adapt to increasing serum potassium concentrations. In patients with renal compromise, potassium homeostasis can become impaired.
Data for amino acid composition, fatty acid profile, vitamin K, iodine, kainic acid, inorganic arsenic, as well as various heavy metals have been reported in dulse samples from Denmark, Iceland, and Maine. Dulse samples from three geographically different North Atlantic harvesting areas have been tested for arsenic, cadmium, lead, mercury, and other metals. Arsenic ranged from 5.5 to 7.5 micrograms per gram of dry weight, cadmium from 0.97 to 2.65, and lead from 0.69 to 3.5. Mercury was barely detectable at less than 0.02 micrograms per gram. These levels are generally low compared to some brown seaweeds, particularly for arsenic.
Challenges include compositional variability, seasonal and geographic influences, and risks of contaminants such as heavy metals, iodine, and microbial hazards.
Dulse contains the neurotoxic amino acid kainic acid, with levels ranging from trace amounts to approximately 560 µg/g dry weight. Concentrations of kainic acid in dulse can vary from below the limit of detection to concentrations exceeding 10,000 mg/kg dry weight in some individual plants. Cultivation of P. palmata for human consumption with very low levels of kainic acid can occur. Research has reported that human safety standards have yet to be established.
Based on its iodine content, dulse may interact with thyroid hormone medications (levothyroxine) by altering iodine status and consequently TSH levels, as demonstrated in the Allsopp 2016 RCT. Due to its very high potassium content, patients taking potassium-sparing diuretics (such as spironolactone, amiloride), ACE inhibitors, or angiotensin receptor blockers (all of which reduce renal potassium excretion) face a potential risk of hyperkalemia when consuming dulse in significant amounts, particularly in the presence of any degree of renal impairment. In the reported case, it is contended that although the patient was predisposed to developing hyperkalemia by her illness and medications, its precipitation was triggered by the high potassium load obtained from the dulse; in this way, her illness and medications were necessary for the hyperkalemia, but not in and of themselves causative.
The composition of biologically active compounds in seaweeds varies due to environmental growth factors, resulting in different compositions even within the same species across the globe. Results suggest a more favourable macroalgae composition in June, with a higher content of most nutrients, minerals, and bioactive compounds. October specimens were richer only in carbohydrates and carotenoids. This variability makes it difficult to standardise doses or extrapolate nutritional data from one product to another.
Health conditions that Dulse may help support.
Body systems that Dulse may help support.
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