Kelp represents several species of iodine-rich edible seaweed.

[LFODPKM ] Letter Key

Latin Name

Laminaria, Macrocystis, Nereocystis, Fucus species

Family

Phaeophyta

Other Common Names

Kombu

Description

• The term kelp can be applied to a variety of brown seaweeds, primarily in the order Laminariales, which includes Laminaria, Macrocystis, and Nereocystis.
• Another brown algae, bladderwrack (Fucus vesiculosis), in the order Fucales (rockweed), is also called kelp (1).
• Brown algae are annual plants common in temperate and polar climates; they differ from most plants by storing food as laminarin (an unusual polysaccharide) or oil rather than starch.
• Some giant kelps can grow as much as 60 m in one season (2).

Part Used

Whole plant

Known Active Constituents

• Algin, or sodium alginate, a high molecular weight polysaccharide common to all brown algae (amounts vary from 12% to 45%).
• Kelp also contains significant amounts of iodine in highly variable amounts; Fucus vesiculosis from the Baltic Sea contains 0.03% iodine, and from the North Sea 0.1%; some species of Fucus may contain up to 0.5% iodine (1). Kelp also contains significant amounts of potassium and sodium.

Mechanism/Pharmacokinetics

• Algin is gel-forming and may be responsible for a laxative effect.
• Iodine can stimulate the production of thyroid hormones in those deficient in this mineral.

[Outline]

• LLatin Name
• FFamily
• OOther Common Names
• DDescription
• PPart Used
• KKnown Active Constituents
• MMechanism/Pharmacokinetics

[CAO ] Letter Key

Clinical Trials

• Thermogenic properties
  • Laminaria digitata and other plants were tested for thermogenic properties in humans. Four subjects were treated with Laminaria tincture. Calorimetric and cardiovascular measures were taken at baseline and at five consecutive timepoints 45 minutes apart. A significant rise in heart rate was seen, but no significant change in blood pressure, energy expenditure, or respiratory quotient (3).
• Strontium absorption
  • In 14 humans given alginate syrup or bread with stable strontium, absorption of strontium was significantly reduced (4). Radioactive strontium absorption in rats was significantly reduced by sodium alginate from different species of algae, including kelp species, but sodium alginate from Sargassum siliquastrum was superior.

Animal/In Vitro

• Cancer
  • Rats fed a diet containing 5% Laminaria had a lower risk of developing 9,10 dimethyl-1,2 benzanthracene (DMBA)-induced mammary tumors. Treated rats had a significant delay to the time of tumor (p = 0.007) and had fewer adenocarcinomas per rat (p < 0.05) (5).
  • In rats, intake of two kelp species (as well as several other seaweeds) decreased tumors induced by the carcinogen 1,2-dimethyl-hydrazine (6). Laminaria extract also reduced the incidence of sarcoma-180 in mice (7).

Other Claimed Benefits/Actions

• Constipation
• Weight loss
• Bronchitis
• Emphysema
• Asthma
• Indigestion
• Ulcers
• Colitis
• Gallstones
• Genitourinary tract problems
• Arthritis
• Skin problems

[Outline]

• CClinical Trials
  • Thermogenic properties
  • Strontium absorption
• AAnimal/In Vitro
  • Cancer
• OOther Claimed Benefits/Actions

[AD ] Letter Key

Adverse Reactions

• Toxic metals
  • Fifteen samples of kelp-containing dietary supplements sold in United Kingdom were found to contain low levels of total and inorganic arsenic (not enough to exceed a safe daily dose) (8).
  • Relatively high concentrations of cadmium and lead (more than 100 µg/100 g) were found in kelp from the Canadian Arctic (9).
• Iodine
  • Iodine concentrations vary widely; a survey of 15 samples of kelp-containing dietary supplements found that in several cases iodine intake could exceed 1,000 µg/day (8).
• Hyperthyroidism
  • A 72-year-old woman developed hyperthyroidism while ingesting kelp (Vitalia) tablets. Six months after discontinuing the kelp tablets, her hyperthyroidism had disappeared (10). A similar case was reported in a 50-year-old woman who took six iodine-containing kelp tablets (Kelpasan) containing 200 mg of kelp each; she developed hyperthyroidism within 2 months that resolved spontaneously following discontinuation of tablets (11). A case of iodide-induced goiter in a patient with Hashimoto’s thyroiditis has been associated with excessive seaweed consumption (12).
  • Seaweed is rich in iodine. Healthy people can consume large amounts of iodine without apparent ill effect; on the Japanese island of Hokkaido, inhabitants consume up to 80,000 µg iodine a day (13). High dietary intake of iodine decreases the incidence of nontoxic diffuse goiter and toxic nodular goiter without affecting the incidence of Graves’ disease or Hashimoto’s disease (13).
• Carotenodermia
  • Carotenodermia from excessive consumption of seaweed to lose weight was reported in a 22-year-old woman (14).
• Rash
  • Two cases of acneiform eruption were related to excessive consumption of kelp tablets obtained at the health food store. In both cases the eruptions disappeared when kelp was discontinued (15).

Drug Interactions

High dietary iodine levels may interfere with thionamide drugs (13).

[Outline]

• AAdverse Reactions
  • Toxic metals
  • Iodine
  • Hyperthyroidism
  • Carotenodermia
  • Rash
• DDrug Interactions

Common Dosage Forms

• Dried thallus: 0.8 to 2 g total daily dose
• Liquid extract: (1:1, 25% ethanol) 1 to 2 mL total daily dose
• Tincture: (1:5, 25% ethanol) 4 to 10 mL daily dose
• Tablets also available

• Are kelp products used in North America?
• Is eating seaweed good for you?

Q: Are kelp products used in North America?

A: Yes, in both medicine and food. Laminaria "tents", which swell slowly over hours, are used in gynecology as a gentle means of dilating the cervix before induced abortion or other intrauterine procedures.

Algin is used as a thickener in foods and is made into films used as edible sausage casing (16). Fucus vesiculosis is used in clambakes to impart a unique flavor to lobsters and clams steamed over it.

Q: Is eating seaweed good for you?

A: Maybe. It certainly is not harmful. Japanese eat large amounts of seaweed that may range from 4.9 to 7.3 g per person per day; in some areas seaweed may compose 25% of the diet. It may be used as a vegetable in soups, sweets, and salads, as well as part of the base of miso soup (7). It has been hypothesized that Laminaria may protect against breast cancer in humans; however, there is little epidemiologic evidence to support this.

Some seaweeds may contribute significant amounts of vitamin B₁₂ to vegetarian diets. A small study of 21 participants (including one male) who were adherents to a strict uncooked vegan diet called the living food diet found that vegans consuming nori or chlorella (these are not kelp) had serum vitamin B₁₂ concentrations twice as high as those not using the seaweed (17).

1. Foster S, Varro I. Tyler’s honest herbal: a sensible guide to the use of herbs and related remedies, 4th ed. New York: Haworth Herbal Press, 1999:233–235.
2. Curtis H. Biology, 3rd ed. New York: Worth Publishers, 1979.
3. Martinet A, Hostettmann K, Schutz Y. Thermogenic effects of commercially available plant preparations aimed at treating human obesity. Phytomedicine 1999;6:231–238.
4. Gong YF, Huang ZJ, Qiang MY et al. Suppression of radioactive strontium absorption by sodium alginate in animals and human subjects. Biomed Environ Sci 1991;4:273–282.
5. Teas J, Harbison ML, Gelman RS. Dietary seaweed (Laminaria) and mammary carcinogenesis in rats. Cancer Res 1984;44:2758–2761.
6. Yamamoto I, Maruyama H. Effect of dietary seaweed preparations on 1,2-dimethylhydrazine-induced intestinal carcinogenesis in rats. Cancer Lett 1985;26:241–251.
7. Teas J. The dietary intake of Laminaria, a brown seaweed, and breast cancer prevention. Nutr Cancer 1983;4:217–222.
8. Norman JA, Pickford CJ, Sanders TW et al. Human intake of arsenic and iodine from seaweed-based food supplements and health foods available in the UK. Food Addit Contam 1987;5:103–109.
9. Chan HM, Kim C, Khoday K et al. Assessment of dietary exposure to trace metals in Baffin Inuit food. Environ Health Perspect 1995;103:740–746.
10. Shilo S, Hirsch HJ. Iodine-induced hyperthyroidism in a patient with a normal thyroid gland. Postgrad Med J 1986;62:661–662.
11. de Smet PA, Stricker BH, Wilderink F et al. [Hyperthyroidism during treatment with kelp tablets] (in Dutch). Nederlands Tijdschrift voor Geneeskunde 1990;134:1058–1059.
12. Okamura K, Inoue K, Omae T. A case of Hashimoto’s thyroiditis with thyroid immunological abnormality manifested after habitual ingestion of seaweed. Acta Endocrinol 1978;88:703–712.
13. Hetzel BS, Clugston GA. Iodine. In: Shils ME, Olson JA, Shike M et al, eds. Modern nutrition in health and disease, 9th ed. Baltimore: Williams & Wilkins, 1999:253–264.
14. Nishimura Y, Ishii N, Sugita Y et al. A case of carotenodermia caused by a diet of the dried seaweed called Nori. J Dermatol 1998;25:685–687.
15. Harrell BL, Rudolph AH. Kelp diet: a cause of acneiform eruption [Letter]. Arch Dermatol 1976;112:560.
16. Facciola S. Cornucopia II: a source book of edible plants. Vista CA: Kampong Publications, 1998:258.
17. Rauma AL, Torronen R, Hanninen O et al. Vitamin B-12 status of long-term adherents of a strict uncooked vegan diet ("living food diet") is compromised. J Nutr 1995;125:2511–2515.