Kelp Supplements Review
Choose the Best Kelp
Supplement. Be Cautious With Kelp! Only 50% of
Supplements Pass CL's Review.
Medically reviewed and
edited by Tod Cooperman, M.D. 
Last Updated
: 11/29/2021 | Initially Posted:
04/22/2017Latest Update: Caution With Seaweed Salts
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Table of Contents
Summary
·
Do I need it? Kelp supplements may contain small
amounts of a variety of vitamins and minerals, but they are primarily a source
of iodine — easily providing the daily requirement in a small pill or serving
of powder. (See What It Is)
·
Why take a kelp supplement for iodine? People are
generally not deficient in iodine unless they follow a restrictive diet,
avoiding iodized table salt (be aware that specialty salts are
not iodized), dairy, bread, and/or seafood. However, pregnant and nursing women
should supplement with iodine. You don't have to take a kelp supplement to get
iodine. Taking a supplement containing potassium iodide (common in
multivitamins) is just as good and may be a safer choice since you're more
likely to get the listed amount of iodine, there is less likelihood of
contamination with arsenic or other heavy metals, and iodine from kelp appears
to be absorbed only half as well as that from a potassium iodide supplement.
Nevertheless, if you prefer a natural source of iodine, a carefully chosen kelp
supplement can be fine.
·
What else can kelp do? Kelp supplements have been promoted for
increasing energy and for weight loss. This has not been clinically proven, but
such effects are possible when iodine in kelp treats underlying hypothyroidism
due to iodine deficiency (See What It Does)
·
How's the quality of kelp supplements? You need to be very
careful. ConsumerLab's tests in this Review found
that half of the iodine supplements contained approximately twice as much
iodine as listed on their labels, which is a safety concern. In addition, one
of these was contaminated with arsenic, a toxin. It is not clear if any
particular kelp plant species or harvesting location is better than another
(See What CL Found).
·
Best Choice? Among the kelp supplements which contained their listed
amounts of iodine and did not exceed contamination levels for arsenic or other
heavy metals, CL chose one (costing just 1 cent per dose) as its Top Pick.
·
How much to take? Adults generally need 150 mcg of iodine
per day, but this increases with pregnancy and lactation. To get 150 mcg of
iodine you need about 30 mg to 150 mg of kelp powder, or less if using a kelp
extract (which is more concentrated in iodine) (See ConsumerTips™).
·
Cautions: Since many kelp supplements contain too much iodine and
may be contaminated, you must choose a product carefully. Women who are
pregnant or nursing should get iodine from a supplement containing potassium
iodide rather than from a kelp supplement. (See Concerns and Cautions).
What It Is:
The
term kelp refers to several genera and species of brown algae that grow in the
ocean. Common kelp species found in supplements include Laminaria hyperborea, Laminaria digitata, Laminaria setchelli, Macrocytis
integrifolia, Macrocystis pyrifera. These species
grow in the northern Atlantic and Pacific oceans. Another brown alga found in
supplements is Ascophyllum nodosum; it is commonly known as
rockweed, but sometimes loosely referred to as kelp (i.e.
"Norwegian kelp" or "knotted kelp"). It grows on the
northwest coast of Europe, and the northeast coast of the U.S.
Kelp, and other edible seaweeds such as kombu (Laminaria japonica) and
nori (Porphyra yezoensis)
are commonly consumed in countries such as China, Korea and Japan as "sea
vegetables" and are a staple of traditional Asian cuisine.
Kelp contains a number of vitamins, such as folate, vitamin A, E & K, and
minerals such as calcium, magnesium and potassium. However, it is best known as
a rich source of iodine. Kelp accumulates iodine from seawater, and is more
efficient in doing so than any other living organism. Laminaria
digitata is known to accumulate the highest amounts of iodine (Küpper Proc Natl Acad Sci
USA 2008). However, the same species was also found to have
the highest levels of arsenic (a toxin) in a study of seaweed species harvested
in New England (Taylor, Chemosphere, 2016).
What It Does:
Preventing/treating iodine deficiency
The iodine in kelp can effectively prevent and treat iodine deficiency —
although you may need a higher dose of iodine from kelp than from a potassium
iodide supplement. For example, a nine-year-old boy with a condition
which required a restrictive diet (including no dairy) was diagnosed with
hypothyroidism caused by iodine deficiency. After online research, his mother
began to supplement him with a kelp supplement providing 400 mcg of iodine per
capsule (number of capsules not reported). After three weeks, his thyroid
hormone levels returned to normal, and remained normal after 7 months of
continued supplementation (Brooks, J Pediatr Endocrinol Metab 2014). In a small study in Britain among
healthy young women (ages 22 to 34) who were not pregnant and had low
self-reported dietary intakes of iodine, daily supplementation for two weeks
with one 500 mg capsule of Ascophyllum nodosum, which provided the
equivalent of 356 mcg of iodine, significantly increased average urinary iodine
excretion (a measure of iodine status) from 78 (mildly insufficient) to 145
mcg/L (adequate) (Combet, Br J Nutr 2014).
However, the study found that iodine from the seaweed was not absorbed as well
as an equivalent amount of iodine from a potassium iodide supplement: 33% of
the iodine from seaweed was bioavailable vs. 59% of the iodine from a potassium
iodide supplement. This study suggests that one absorbs only about half
as much iodine from kelp as from a potassium iodide supplement.
Iodine is essential for healthy functioning of the thyroid gland which, among
other things, controls the body's metabolism, and, during pregnancy and
infancy, influences bone and brain development. In the U.S., manufacturers
voluntarily add iodine to table salt. Most people get enough iodine from their
diets, however women who are pregnant require more iodine and people who don't
consume table salt may be at risk for deficiency (see ConsumerTips™). Also, those who follow a diet consisting of
mainly plant-based
proteins may also be at risk for low levels of iodine.
Iodine deficiency causes hypothyroidism (underactive thyroid), which can cause
impaired mental function and a range of other symptoms, as well as enlargement
of the thyroid. This enlargement of the thyroid, called goiter, is often the
first sign of deficiency. Deficiency may also increase the risk of the
follicular form of thyroid cancer.
Mild to moderate iodine deficiency during pregnancy is associated with an
increased risk of attention deficit hyperactivity disorder (ADHD) in offspring,
while more severe deficiency can cause neurodevelopmental deficits and growth
retardation in the fetus, miscarriage and stillbirth. Cretinism, a condition
characterized by stunted growth, mental retardation, deaf mutism, and other
abnormalities, can also occur.
Iodine deficiency In infants and children can cause lower than average
intelligence and other neurodevelopmental issues.
It's possible that kelp supplementation may be helpful as an alternative source
of iodine for people with iodine deficiency who also maintain a low-salt diet;
however, there do not appear to be any clinical studies investigating kelp
supplements for this use.
Energy and Weight Loss
Kelp supplements are sometimes promoted for energy and weight loss, due in
part, to the fact that iodine is needed for healthy thyroid function.
Hypothyroidism (underactive thyroid) can cause fatigue and weight gain.
However, there is no evidence that kelp supplementation increases energy or
promotes weight loss in people who don't have underactive thyroids.
Additionally, a gel-like substance that can be produced from kelp plant cell
walls, called alginate, has shown some promise in reducing appetite and
lowering blood sugar after eating (Paxman, Appetite 2008; Hoad,
J Nutr 2004); however,
alginate is a specially prepared, gel-forming extract. It's not known if
consuming the dried kelp in regular kelp supplements (such as the ones in this
review) has any effect on appetite, blood sugar or weight. One small study
among healthy young men in Britain who consumed bread enriched with a
branded Ascophyllum nodosum ingredient (Seagreens)
found the enriched bread reduced energy intake at a subsequent meal (4 hours
later) by 16.4% compared to consuming bread which was not enriched; however,
there were no significant reductions in hunger, fullness, or blood sugar levels
(Hall, Appetite 2012).
Quality Concerns and
Tests Performed:
Kelp
supplements can be a safe source of iodine but can potentially be contaminated
with arsenic (Amster, Environ Health
Perspect 2007). However,
neither the FDA nor any other federal or state agency routinely tests kelp
supplements for quality prior to sale. Consequently, ConsumerLab.com purchased
and tested kelp supplements to determine if they contained listed amounts of
iodine — typically the only nutrient listed on the Supplement Facts panels of
kelp supplements -- as well as arsenic and other heavy metals (lead, cadmium,
and mercury). Standard tablets and caplets were also tested to be sure that
they would disintegrate ("break apart") properly (see Testing Methods and Passing Score).
What CL Found:
Only half of the six kelp supplements ConsumerLab.com selected
and tested met its quality standards. Through ConsumerLab.com's
voluntary Quality Certification Program,
in which products undergo the same testing, an additional two products were
found to meet CL's quality standards. All tablet products were able to properly
disintegrate.
The three products which were "Not Approved" were each discovered to contain much
more iodine than expected from their labels: 177% to 207% of their listed
amounts. Per serving, this amounted to hundreds of additional micrograms of
iodine and daily total amounts of 531 mcg to 964 mcg — levels considered very
high. In addition, one product was contaminated with arsenic (discussed
below).
Specifically, ConsumerLab found the following
results, which were confirmed in a second independent laboratory:
·
Nature's Answer Kelp Thallus contained 683.8 mcg of iodine instead of
the listed 330 mcg per capsule (207.2% of the listed amount).
·
Progressive Laboratories Kelp contained 964.2 mcg of iodine instead of
the listed 500 mcg per capsule (192.8% of the listed amount). In
addition, it was found to be contaminated with arsenic, containing just over 5
mcg of inorganic arsenic (the most toxic form) per capsule (see "Arsenic risk" below).
·
Traditional Foods Market Kelp Powder contained 531 mcg
of iodine instead of the listed 300 mcg per suggested daily serving (which is
listed as 3/64th of a teaspoon) (177%
of the listed amount).
The amounts of iodine in
these three products far exceed FDA "safe" limits for iodine
from kelp in supplements. Even the amounts listed on Nature's
Answer and Progressive Laboratories products exceed
this limit. FDA regulations indicate
that "kelp may be safely added" to supplements as a source of iodine
provided that a daily serving does not provide in excess of 225 mcg of
iodine. For products labeled for use by specific individuals, other limits
apply: For infants: 45 mcg, for children under age 4: 105 mcg, for adults and
children 4 or more years of age: 225 mcg, and for pregnant or lactating women:
300 mcg.
Too much iodine (typically over 1,000 mcg daily from all sources for adults)
can cause some of the same symptoms as iodine deficiency, including goiter (an
enlarged thyroid gland). High iodine intakes can also cause thyroid gland
inflammation and thyroid cancer. Very large doses (several grams) can cause
other adverse effects (as discussed in Concerns and Cautions).
Arsenic risk:
Arsenic is a toxin which can occur in kelp supplements (Amster, Environ Health
Perspect 2007). The
inorganic form of arsenic is a carcinogen (causing bladder, lung, and skin
cancer and, potentially, liver, kidney, and prostate cancer) and can also have
detrimental effects on organs and the circulatory system. Although there are no
established federal limits for contaminants in supplements, the Environmental
Protection Agency (EPA) has indicated that no amount of arsenic is considered
"safe." The EPA considered a limit of 5 mcg of arsenic per liter of
drinking water, but concluded that 10 mcg (which includes the inorganic plus
the potentially less toxic organic form -- although the majority of arsenic in
water is believed to be inorganic) provided a balance between safety and the
cost of reducing arsenic levels in water systems. New Jersey adopted the more
conservative 5 mcg limit for total arsenic. California, out of concern
for reproductive effects, has proposed that a product with
more than 0.5 mcg of inorganic arsenic in a daily serving carry a related
warning label. As a carcinogen, California applies a limit of 10 mcg of
inorganic arsenic per daily serving before a warning label is required.
The amount of arsenic in Progressive Laboratories Kelp exceeded
the California limit for reproductive harm and the New Jersey limit for a liter
of water, and it is right at the EPA's water limit and California's limit for
carcinogens.
CL's screening for arsenic in supplements was two-staged, first looking for
total arsenic and then, if 10 mcg or more per daily serving was found,
measuring the amount of inorganic arsenic. Only Progressive triggered
the second step, although, interestingly, the other two "Not Approved" products (Nature's
Answer and Traditional Foods) had significantly higher
levels of total arsenic than the other supplements. The
product with the lowest amount of total arsenic among the supplements was Natural
Factors Liquid Kelp, which contained just 0.018 mcg per serving (1 drop),
likely because it is a liquid extract.
Top Pick:
Among
the kelp supplements which were Approved, CL's Top Pick is Swanson
Kelp at 1 cent per tablet. Although Nature's Life
Icelandic Kelp is the same cost per tablet, it is a kelp powder while Swanson is
a kelp extract which helps reduce the risk of potential
arsenic contamination. Both of these products provide 225 mcg of iodine per
pill, meeting the FDA definition of "safe" for adults and children
over age 4.
Although far above the FDA's "safe" limit, should you be directed by
a health professional to get a higher dose of iodine and you want to get it
from kelp, the best option would be Natural Factors Liquid Kelp,
which provides 800 mcg of iodine per drop, costing just a penny. It also
contained less arsenic than all other kelp supplements tested, as noted
earlier. Bear in mind that it contains more than the U.S. FDA "safe"
limit of iodine (it is a Canadian product, but can be purchased by Americans
online) and make sure to limit dosing to just 1 drop.
Test Results by Product:
Listed
alphabetically below are the test results for eight kelp supplements. Six of
these were selected by ConsumerLab.com and two others (each indicated with a CL
flask) were tested at the request of their manufacturers/distributors through ConsumerLab.com's Quality Certification Program.
Also listed is a product that is very similar to another that was Approved but
is sold under a different brand name.
Products listed as "Approved" met their label claim and ConsumerLab.com's standards for kelp supplements. Also
shown for each product is the serving size recommended on the label, the listed
source of kelp, and the amount of iodine in the recommended daily serving. In
the last column is the price paid, cost per suggested serving, calculated cost
of to obtain 225 mcg of iodine, as well as notable features and additional
ingredients. The full list of ingredients is available for each product by
clicking on the word "Ingredients" in the first column.
|
RESULTS OF CONSUMERLAB.COM TESTING OF KELP SUPPLEMENTS |
|||||||
|
Product Name, Serving
Size, and Suggested Daily Serving on Label |
Listed Amount of Kelp
and Genus/Species |
--TEST RESULTS-- |
Cost For Daily
Suggested Serving On Label |
||||
|
OVERALL RESULTS: |
Contained Labeled
Amount of Iodine |
Did Not Exceed
Contamination Limit for Lead, Cadmium and Arsenic |
Disinte-grated Properly |
||||
|
|
Amount of kelp not
listed |
APPROVED.
CAUTION: HIGH DOSE |
|
|
NA |
$0.01 |
|
|
|
83 mg thallus extract |
NOT |
Found 207.2% of listed
iodine: 683.8 mcg per capsule |
|
NA |
$0.04 |
|
|
|
41 mg kelp (powder) |
APPROVED |
|
|
|
$0.01 |
|
|
|
167 mg3 kelp (powder) |
NOT |
Found 192.8% of listed
iodine: 964.2 mcg3 per capsule |
Found 9.6 mcg3 arsenic (58 mcg per g) and 5.4 mcg3 inorganic arsenic (32.8 mcg per g) per capsule |
NA |
$0.133 |
|
|
|
Amount of kelp not
listed |
APPROVED |
|
|
|
$0.05 |
|
|
|
59 mg kelp extract |
APPROVED |
|
|
|
$0.01 |
|
|
|
156 mg organic kelp
(powder) |
NOT |
Found 177% of listed
iodine: 531 mcg per 3/64th teaspoon |
|
|
$0.01 |
|
|
|
Amount of kelp not
listed |
APPROVED |
|
|
|
$0.04 |
|
|
Similar to Approved Products*: |
|||||||
|
Puritan's Pride® Premium Sea Kelp (1 tablet,
once daily) |
Similar to Vitamin
World Sea Kelp. |
$0.03 |
|||||
|
|
|||||||
|
Unless otherwise noted, information about the products
listed above is based on the samples purchased by ConsumerLab.com (CL) for
this Product Review. Manufacturers may change ingredients and label
information at any time, so be sure to check labels carefully when evaluating
the products you use or buy. If a product's
ingredients differ from what is listed above, it may not necessarily be of
the same quality as what was tested. |
|||||||
|
Copyright ConsumerLab.com, LLC, 2017. All rights reserved.
Not to be reproduced, excerpted, or cited in any fashion without the express
written permission of ConsumerLab.com LLC. |
|||||||
ConsumerTips™:
The recommended daily allowances (RDAs) for iodine are listed in
micrograms and are: 90 mcg for children ages 1 to 8, and 120 mcg for children
ages 9 to 13. For both males and females ages 14 and older, the RDA is 150 mcg.
However, for pregnant women it is 220 mcg, and for lactating women it is 290
mcg. You may already be getting adequate intake of iodine from your diet (such
as from iodized table salt, dairy, and breads -- although the amounts in dairy
and breads is highly variable depending on the practices of the supplier). (Be
aware that specialty salts, such as
Himalayan salt, are not iodized). Many multivitamin/multimineral supplements
often include iodine (typically 150 mcg from potassium iodide) — you can check
which ones do by looking at the Mineral Ingredients comparison
table in ConsumerLab's Multivitamin/Multimineral
Review.
If you decide to obtain iodine from a kelp supplement, be sure to choose one
that has been Approved by ConsumerLab.com (see Results Table above) to help ensure it
contains the amount of iodine listed on its label and does not exceed
contamination limits for heavy metals such as arsenic. Kelp powders (dried
kelp) are about 0.1 to 0.5% iodine, so to get 150 mcg of iodine you need about
30 mg to 150 mg of kelp powder, or less if using a kelp extract (which are more
concentrated in iodine). Unless advised otherwise by your healthcare provider,
look for a product that does not exceed the FDA limits for iodine from kelp
supplements: a daily serving should not provide more than 225 mcg of iodine for
adults and children over the age of four, as noted in the What CL Found section. Also, keep in mind
that you may only be absorbing half as much iodine from kelp as you would from
a potassium iodide supplement, so, if you are relying heavily on kelp as your
iodine source, you may want to take a dose that provides somewhat more than
your RDA for iodine: a serving of kelp which lists 225 of iodine would not be
excessive for an adult needing 150 mcg of iodine daily.
Concerns and Cautions:
Due to
the risk of contamination with arsenic in kelp, women who are pregnant
or nursing but require iodine supplementation should get iodine from
supplements containing potassium iodide rather than from a kelp supplement.
Congenital hypothyroidism has been reported in infants born to
mothers taking an herbal supplement high in iodine-containing kelp (Stagi, Horm Res Paediatr 2010).
High doses of iodine from kelp supplements potentially increase or
decrease certain thyroid hormones (Clark, Endocrin Pract 2003; Eliason, J Am Board Fam Pract 1998). For example,
a significantly elevated TSH (thyroid stimulating hormone) level was found in a
54 year-old woman with hypothyroidism who was not
taking levothyroxine but took excessive iodine (2,730 mcg per day) from
supplements (including kelp supplements and calcium and B vitamin formulas
containing iodine) for 11 days. Her TSH increased to 21.3 mU/mL
from 8.4 mU/mL prior to supplementation. This was discovered
when she was hospitalized for an altered mental state with episodes of
combativeness, screaming spells, and violent behavior as well as slow heart
rate and low blood pressure. Her symptoms improved after treatment with
intravenous levothyroxine (Gaby, Am J Thera 2018).
High iodine intakes can also cause thyroid gland inflammation and thyroid
cancer. Due to the risk of potential iodine-induced thyroid dysfunction, the
American Thyroid Association recommends advise that no individual consume an
iodine or kelp daily supplement containing more than 500 mcg of iodine unless
advised otherwise by your healthcare professional (Leung, Nat Rev Endocrinol 2014). Upper
tolerable intake levels (ULs) established by the Institute of Medicine for
iodine are 200 mcg for children 1 to 3 years; 300 mcg for children 4 to 8
years; 600 mcg for children 9 to 13 years; 900 mcg for teens 14 to 18 years;
and 1,100 mcg for adults.
Very large doses of iodine (several grams per day) can cause burning of
the mouth, throat, and stomach; fever; stomach pain; nausea; vomiting;
diarrhea; weak pulse; and coma.
The iodine in kelp can interact or interfere with anti-thyroid medications used
to treat hyperthyroidism, potentially causing you to produce too
little thyroid hormone.
People taking blood thinning medications such as aspirin, clopidogrel
(Plavix) heparin, ticlopidine (Ticlid), warfarin
(Coumadin), etc. should use kelp with caution because kelp contains
compounds called fucoidans which have anti-platelet and anti-coagulant effects
(Zhao, Thromb
Res 2012; Fitton, Mar Drugs 2015).
As kelp is often harvested from the sea and may have contaminants from other
sea life, it may be prudent to avoid kelp supplements if you are allergic
to shellfish.
Be aware that an autoimmune reaction resulting in abnormal bleeding,
bruising and low blood platelet count was been reported in a women
taking three 550 mg kelp tablets daily for six weeks; symptoms resolved after
medical treatment and stopping supplementation (Pye, Lancet 1992).
In people who are sensitive to iodine, excessive iodine intake
may cause skin reactions (iododermas) including itching,
rash, hives, blisters, purpuric hemorrhagic (red or purple spots caused by
bleeding underneath the skin) or acne outbreaks (Pennington, J Am Diet Assoc 1990). Iodine and
kelp supplements containing iodine may also worsen acne in sensitive
individuals. For example, a 24 year old woman whose moderately severe acne was
almost completely cleared after treatment with antibiotics and topical
medication experienced a sudden, severe acne breakout after consuming a high
daily dose of iodine (10 to 12 kelp tablets containing 15 mg of iodine each);
the outbreak resolved 2 weeks after she stopped taking the tablets (Harrell, Arch Dermatol 1976).
There is also a report of a 28 year old man whose acne did not respond to
traditional treatment, but resolved six weeks after he stopped consuming
iodized salt; when he began consuming iodized salt again, the acne returned
within three weeks (Goihman-Yahr, Int J Derm 2002).
Research suggests that in most people, however, there is no association between
iodine consumption and acne (Hitch, Arch Dermatol 1961; Danby, J Am Acad Dermatol 2006).
Kelp and other seaweeds are used in some salt
substitutes (referred to in some products as "seaweed seasoning,"
"kelp granules," or "table kelp") and may form
harmful byproducts when used along with disinfected tap water for
cooking due to interaction between the iodine in kelp and residual chlorine
compounds in tap water. A laboratory study in China found that heating 5 grams
of seaweed salt in 500 mL chlorinated of tap water for 1 hour increased the
concentrations of iodinated trihalomethanes (which are associated with cancer
and adverse health outcomes) to close to or above EPA limits for
trihalomethanes in drinking water (DeMarini, Environ Mol
Mutagen 2020). Heating iodized salt in similar solutions did
not significantly increase the concentration of trihalomethanes. Iodized salt
contains iodine as iodate (IO3-), which is less likely
to form these compounds compared to products such as seaweed salt, which
contain iodine as iodide (I-) or organic iodine. Iodide readily reacts with
chloramine to form intermediate chemicals that go on to react with organic
compounds (in seaweed and tap water itself) to form these disinfection
byproducts (Cao, Chem Eng
J 2021).
Information on this site
is provided for informational purposes only. It is not an endorsement of any
product nor is it meant to substitute for the advice provided by physicians or
other healthcare professionals. The information contained herein should not be
used for diagnosing or treating a health problem or disease. Consumers should
inform their healthcare providers of the dietary supplements they take.
Latest Clinical Research Updates for Kelp
11/09/2021
Seaweed salts (also known
as seaweed seasoning, kelp granules, or table kelp) can be used as salt
substitutes, but cooking with them may result in the formation of toxic
byproducts according to a recent study. Get the details in the Concerns and Cautions section of our Kelp
Supplements Review.
Related CL Answers (4)