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Other common
name(s): seaweed, sea veg or sea vegg, sealogica,
seaweed, algae, red algae, green algae, brown algae, kelp, kombu,
bladderwrack, wakami, nori, dulse, and others
Scientific/medical
name(s): Fucus
vesiculosus, Laminaria
digitata, Macrocystis
pyrifera, Porphyra
tenera, and others
Description
Seaweed is a type of algae that grows in or near the sea.
Certain types of seaweed and other algae have been eaten as food for
thousands of years. Several companies sell seaweed and other algae as
food supplements, either individually or in combinations, and call them
sea vegetables. They have some special uses in medicine and as food
additives.
Overview
Certain types of algae and seaweed have been used as food
throughout history. They have some special uses in medicine and as food
additives. Generally, edible seaweeds are safe for people who are not
allergic.
Despite claims that sea vegetables are super-rich in nutrients
that can prevent cancer and help numerous diseases, there is no
reliable clinical evidence that this is true. Most seaweed does contain
iodine, which is also available in iodized salt. However, amounts of
iodine in seaweed vary widely, and getting too much of iodine can cause
thyroid and skin problems for some people. Early laboratory and animal
studies of seaweed extracts suggest that certain compounds may one day
be used in medicine.
How is it promoted for use?
Proponents claim that sea vegetables contain nutrients that
"regenerate" the body. They maintain that sea vegetables are
concentrated, containing several times more nutrients than land
vegetables. Marketers often claim that seaweed will regulate body
weight, and that taking seaweed supplements will reduce food cravings.
In Infomercials set up to look like interviews have claimed that
"degenerative diseases," including tuberculosis, fibromyalgia, cancer,
asthma, and diabetes are due to nutritional deficiencies. They claim
that these problems can be prevented or helped by nutrients in sea
vegetables, which they say offer nutrients that cannot be found
elsewhere. For example, some of these proponents say that the iodine
added to salt cannot be used by the body, while organic iodine from
seaweed is easily absorbed.
What does it involve?
Most sea vegetables are dried after being harvested. If they
are to be used as supplements, they are ground up and sold as powders,
tablets, or capsules. The marketers of some blends recommend 3 or more
capsules per day. Other sellers suggest different amounts of the dried
plant in capsule form, or suggest blending the dried powders into soups
or other foods. Supplements are sold in health food stores, by phone,
and over the Internet. Some are even recommended for pets as both
vitamin supplements and immune system boosters.
Dried sea vegetables are also sold in Asian and specialty
markets to be prepared as food. Most of these plants must be rehydrated
before use. Some kinds of seaweed, such as nori, are common ingredients
in sushi.
What is the history behind it?
Algae such as kelp (called kombu in Japan), nori, and wakami
have been used in Asian cooking for thousands of years. Many types of
seaweed are known in the United States by their Japanese names. Seaweed
has been used medicinally in China for centuries to treat liver
problems, swelling, phlegm, cysts, and enlarged thyroid glands. (see Traditional Chinese Medicine).
In the 18th century, kelp was discovered as a source of iodine
in the diet and used to treat enlarged thyroid. Called goiter, this
condition is often caused by not getting enough iodine in food. Iodine
was later added to salt to prevent iodine deficiency in the United
States, and the rate of goiter declined dramatically.
Several types of algae have been marketed for use as
supplements since the early 1980s. At that time, spirulina and other
types of blue-green algae that grow in ponds and lakes became popular.
Since then, an ever-increasing variety of seaweeds from ocean sources
have been sold as dietary supplements in the United States. (see Chlorella).
In conventional medicine, stems from kelp were at one time
used to enlarge the cervix for medical procedures, although there are
now man-made devices that can be used. Purified compounds from seaweed
are approved for use in many types of food. Carrageenan gum, a seaweed
extract, is used in foodstuffs to create gels, stabilize mixtures, and
thicken liquids. It is a common ingredient in ice cream, jelly, and
infant formula. Agar, which is made from red algae, is used to add
texture and thickness to foods. It is also a purely vegetable gelatin,
unlike the more commonly used type that is made from animal protein.
Agar has many uses, from clarifying wine to growing bacteria in the
laboratory.
What is the evidence?
Observational studies of people who eat seafood and algae
regularly tend to show that they have less breast cancer than those
whose diet relies more on meat. Women in Japan, for example, have a
lower risk of breast cancer than women in the United States. However,
women who move from Japan to the United States are at the same risk as
U.S. women within a few generations. This suggests that the difference
is not genetic. Even though there are many factors that may be
responsible for the differences in risk—such as other foods,
exposures, or lifestyle—scientists have focused on foods,
such as omega-3 fatty acids in fish, as one possible explanation. The
differences between typical Asian and North American diets and
lifestyles are so numerous, however, that it is unlikely that seaweed
is the only or even the main factor responsible for differences in
cancer risk. For example, soy foods and green tea are also being
studied to see if they influence cancer risk. There are many other
possible explanations yet to be explored.
In laboratory studies and some animal studies, compounds from
several types of algae have slowed the growth of cancer cells and
caused cancer cells to die, often by a process of natural cell death
called apoptosis. However, clinical studies in humans have not been
done using seaweed supplements. It is also important to note that
extracted compounds are not the same as whole algae, and study results
are not likely to show the same effects.
Dried seaweed contains large amounts of some nutrients by
weight because the water is removed. The standard nutritional analysis
is for 3 ½ ounces (100 grams), which in some cases, would be
more than 6 cups of dried seaweed. Actual serving sizes are very small
when using seaweed supplements, and nutrient amounts are not
guaranteed.
The American Cancer Society's nutrition guidelines recommend
eating a balanced diet that includes 5 or more servings a day of
vegetables and fruit, choosing whole grains over processed and refined
foods, and limiting red meats and animal fats in order to help reduce
cancer risk. Eating whole seaweed rather than supplements is a way to
include a larger variety of plant-based foods. It is best to choose
foods from many kinds of fruits, vegetables and other plant sources
such as nuts, seeds, whole grain cereals, and beans. (For more
information, see American Cancer Society
Guidelines on Nutrition and Physical Activity for Cancer Prevention.)
Are there any possible problems or
complications?
This product is sold as a
dietary supplement in the United States. Unlike drugs (which must be
tested before being allowed to be sold), the companies that make
supplements are not required to prove to the Food and Drug
Administration that their supplements are safe or effective, as long as
they don't claim the supplements can prevent, treat, or cure any
specific disease.
Some such products may not
contain the amount of the herb or substance that is written on the
label, and some may include other substances (contaminants). Actual
amounts per dose may vary between brands or even between different
batches of the same brand.
Most such
supplements have not been tested to find out if they interact with
medicines, foods, or other herbs and supplements. Even though some
reports of interactions and harmful effects may be published, full
studies of interactions and effects are not often available. Because of
these limitations, any information on ill effects and interactions
below should be considered incomplete.
Since most seaweeds have varying amounts of iodine and other
nutrients, it is difficult to know how much is in any one supplement.
Edible seaweeds are generally safe for those who are not allergic. In
some people, however, large amounts of iodine can cause goiter
(enlargement of or growths on the thyroid) or other serious health
problems. In people with known thyroid disorders, their conditions may
be made worse by eating kelp or taking seaweed supplements. Eating a
lot of seaweed or getting too much iodine from other sources can cause
skin outbreaks that look like acne.
Some seaweed also contains large amounts of sodium, which may
worsen high blood pressure or heart failure. Depending on where it is
grown, some algae can contain concentrated amounts of heavy metals,
including arsenic. These contaminated supplements have caused serious
toxic effects in the past. Many types of algae are toxic or even fatal
when eaten, so it is important to get supplements from trustworthy
sources. Early or mild symptoms of toxicity may include nausea,
diarrhea, weakness, numbness and tingling.
A recent analysis of dried seaweed samples purchased in London
and over the Internet found that some contained worrisome levels of
arsenic.
Relying on this type of treatment alone and avoiding or
delaying conventional medical care for cancer may have serious health
consequences.
Additional Resources
More information from your American Cancer
Society
The following information on complementary and alternative
therapies may also be helpful to you. These materials may be found on
our Web site (www.cancer.org)
or ordered from our toll-free number (1-800-ACS-2345).
References
Bae SJ, Choi YH. Methanol extract of the seaweed Gloiopeltis
furcata induces G2/M arrest and inhibits cyclooxygenase-2 activity in
human hepatocarcinoma HepG2 cells. Phytotherapy
Research. 2007;21:52-57.
Barrett S. Algae: False Claims and Hype. Accessed at:
http://www.quackwatch.org/01QuackeryRelatedTopics/algae.html on June
10, 2008.
Branger B, Cadudal JL, Delobel M, et al. Spiruline as a food
supplement in case of infant malnutrition in Burkina-Faso. Arch Pediatr.
2003;10:424-431.
Clark CD, Bassett B, Burge MR. Effects of kelp supplementation
on thyroid function in euthyroid subjects. Endocr Pract.
2003;9:363-369.
Dharmananda S. The nutritional and medicinal value of seaweeds
used in Chinese Medicine. Accessed at:
http://www.itmonline.org/arts/seaweed.htm on June 10, 2008.
Growing Concerns over Blue-Green Algae. NCAHF News, 1996
March/April;19, (2). Accessed at: http://www.ncahf.org/nl/1996/3-4.html
on June 10, 2008.
Humbert P. Induced acne. Rev
Prat. 2002;52:838-840.
Kushi LH, Byers T, Doyle C, et al. American Cancer Society
Guidelines on Nutrition and Physical Activity for cancer prevention:
reducing the risk of cancer with healthy food choices and physical
activity. CA: a Cancer
Journal for Clinicians. 2006; 56:254-281.
Medline Plus. Seaweed, Kelp, Bladderwrack. Accessed at:
www.nlm.nih.gov/medlineplus/druginfo/natural/patient-bladderwrack.html
on June 10, 2008.
Müssig K, Thamer C, Bares R, et al. Iodine-induced
thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med.
2006;21:C11-4.
Ostrzenski A. Resectocopic cervical trauma minimized by
inserting Laminaria digitata preoperatively. Int J Fertil Menopausal Stud.1994;39:111-113.
Rose M, Lewis J, Langford N, Baxter M, Origgi S, Barber M,
MacBain H, Thomas K. Arsenic in seaweed--forms, concentration and
dietary exposure. Food
Chem Toxicol. 2007;45:1263-1267
Sekiya M, Funahashi H, Tsukamura K, et al. Intracellular
signaling in the induction of apoptosis in a human breast cancer cell
line by water extract of Mekabu. International
Journal of Clinical Oncology. 2005;10:122-126.
Teas J, Pino S, Critchley A, Braverman LE. Variability of
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USDA National Nutrient Database for Standard Reference.
Accessed at: http://www.nal.usda.gov/fnic/foodcomp/search/ on June 10,
2008.
Walkiw O, Douglas DE. Health food supplements prepared from
kelp -- a source of elevated urinary arsenic. Clin Toxicol.1975;8:325-331.
Yuan YV, Walsh NA. Antioxidant and antiproliferative
activities of extracts from a variety of edible seaweeds. Food Chem Toxicol.
2006;44:1144-1150.
Zhuang C, Itoh H, Mizuno T, Ito H. Antitumor active fucoidan
from the brown seaweed, umitoranoo (Sargassum thunbergii). Biosci Biotechnol Biochem.1995;59:563-567.
Ziegler RG, Hoover RN, Nomura AM, et al. Relative weight,
weight change, height, and breast cancer risk in Asian-American women. J Natl Cancer Inst.
1996;88:650-660.
Note: This information may not cover
all possible claims, uses, actions, precautions, side effects or
interactions. It is not intended as medical advice, and should not be
relied upon as a substitute for consultation with your doctor, who is
familiar with your medical situation.
Last Medical Review: 11/01/2008
Last Revised: 11/01/2008
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