Kelp has been an essential component of East Asian diets for centuries. In fact, this diet introduced kelp into different regions across the world. The health benefits of kelp are wide-ranging — it can help reduce blood pressure, fight iodine deficiency, and may even be an effective treatment for hepatitis C and certain types of cancer. Read on to find out more.

What Is Kelp?

Kelp, or brown algae, is found on the coasts of Korea and Japan. Kelp can have many therapeutic and nutritional benefits, as it is a rich source of iodine, minerals, antioxidants, fiber, proteins, and healthy carbohydrates. Kelp also reduces inflammation, fights diabetes, and protects the heart and brain [1].

Kelp Nutrition

Kelp is an excellent source of iodine, potassium, magnesium, iron, and calcium [2].

Depending on the type of kelp or seaweed, the nutrient profile can vary greatly [3].

Laminarin is a specific type of kelp in the brown algae family rich in nutrients (iodine, potassium, magnesium, calcium, and iron). It also blocks tumor growth and spreading [2].

Another type of seaweed — Gracilaria changii — is rich in fiber content and essential amino acids (the building blocks of proteins) [4, 3].

Kelp also contains a complex long-chain carbohydrate (polysaccharide) called fucoidan. Fucoidan grants kelp cancer fighting, antioxidant, and anti-inflammatory properties, among others [5, 6, 7, 7].

Kelp is also an excellent source of vanadium, used in clinical studies to lower glucose levels in individuals suffering from diabetes type 1 and 2. Fucoxanthin, a pigment found in brown seaweed, also boosts weight loss [8, 9, 10, 11, 12].

Mechanism of Action

The high iodine content in kelp supports the production of thyroid hormones T3 and T4. If iodine deficiency is severe and prolonged, the thyroid gland enlarges and forms a goiter. This can also lead to a lack of thyroid hormones (hypothyroidism) [13, 2].

Kelp has cancer-fighting properties. Fucoidan from kelp plays a role in killing cancer cells and stopping their growth. Fucoidan affects cell growth, causing cell death (apoptosis) in tumor cells [5].

Nutrients from seaweed carry important health benefits. Dietary fiber, peptides, lipids, and minerals protect the heart. Sea algae reduce markers of heart disease, protects the cells (reducing oxidative stress), reduces inflammation in blood vessels, reduces high blood pressure, and decreases blood clotting [14].

Health Benefits of Kelp

1) Improves Iodine Deficiency

Iodine deficiency is the main cause of low thyroid hormone levels. Deficiency during pregnancy can lead to severe mental and cognitive development issues in children. It can impair reproductive function, or cause brain damage or permanent intellectual disability during childhood [13].

Kelp has a high iodine content (200 to 400 µg). It improved thyroid function in a study (longitudinal) of 7 patients with severe motor and intellectual disabilities and hypothyroidism due to iodine deficiency. Patients were given 1 to 2 grams of powdered kelp daily, and this treatment restored thyroid function, increasing the concentration of iodine in the urine [15].

2) May Reduce Sugar in Diabetes

Powdered seaweed pills reduced sugar levels in a study of 20 subjects with type 2 diabetes (RCT), taken daily for 4 weeks. It decreased fasting and post-meal blood sugar levels and serum lipid (fatty acid) levels. Also, the pills increased HDL levels, which help prevent heart disease associated with diabetes [16, 17, 18].

Kelp is a great source of vanadium. Oral vanadium supplements (150 to 300 mg daily) given to 14 type 1 diabetic patients (longitudinal study) for 30 months decreased fasting blood sugar levels by over 30%. Vanadium also decreased cholesterol levels. It caused no major side effects, with the exception of mild diarrhea at the beginning of the treatment period [19, 10].

Vanadium mimics insulin in animal studies. In one study with diabetic mice, a vanadium-based compound reduced blood sugar levels and diabetic symptoms (such as thirst, hunger, and weight loss), with no side effects [20].

3) May Fight Cancer

A study of 15 postmenopausal women, 10 of whom were breast cancer survivors, looked at the effects of brown seaweed supplementation over a 3-month period (alternating with placebo). Seaweed decreased an important marker of breast cancer recurrence by half (receptor uPAR) after 4 weeks [21, 22, 22].

Fucoidan, a key component of seaweed, may fight cancer and stop tumor growth, based on both cell and animal models (review). In addition, seaweed supplements and algae extracts, including the brown seaweed Laminaria, reduced colon, breast, and prostate cancer activity (review) [23, 24, 25, 26].

Fucoidan injections or fucoidan, when given in food, slowed tumor growth in mice. Fucoidan killed cancer cells by activating the immune system (via natural killer cells) [23, 27].

Fucoidan reduced tumor growth and killed 2 out of 4 leukemia cell lines. In another cell study, fucoidan stopped the growth and spread of lung cancer cells, by blocking growth pathways (AktmTOR and NF-kB) [28, 29, 30, 27].

4) May Treat Hepatitis C

In a study of 15 patients with chronic hepatitis C, fucoidan from brown seaweed was used to treat virus-related liver diseases. After 8 to 10 months of treatment, hepatitis C virus (HCV) levels in the blood significantly decreased [31].

Additionally, this study also examined alanine aminotransferase levels, a protein whose presence correlates to a more severe HCV infection. The blood tests also present a decrease in alanine aminotransferase levels. Despite the positive laboratory findings, these results did not lead to significant clinical improvements [31, 32].

5) Helps Fight Inflammation

In a rat model, fucoidan (present in kelp) was used to reduce inflammation caused by immune cells in the brain. Fucoidan improved animal behavior, reduced harmful compounds (TNF-alpha), prevented neuron loss, and protected the cells from damage (reducing reactive oxygen species) that can cause neurodegeneration [33, 34, 35]

In a brain and spinal cord cell study, fucoidan reduced inflammation (blocking nitric oxide (NO) and prostaglandin E2 production). Fucoidan also blocked inflammatory proteins (cytokines IL-1β and TNF-alpha) and the inflammation pathway (reducing NF-kβ and p38 MAPK) [6, 36, 34, 37, 38, 39, 40].

Fucoidan reduces all important actors in the inflammatory cascade. In brain immune cells (microglia) fucoidan from brown seaweed showed promise for treating neurodegenerative diseases caused by inflammation [6, 41, 42].

6) May Boost Weight Loss

A study of Xanthigen, which is a type of kelp, showed reduced body weight, waist circumference, and body and liver fat content in 151 non-diabetic obese women. In this study, 75% had a non-alcoholic fatty liver disease and 25% had a normal liver). It also improved liver function tests and increased energy use at rest [43].

Mice fed fats from seaweed had increased markers of weight loss in fat tissue. Fucoxanthin, a pigment from seaweed, produced these effects [12, 44].

In a cell study, alginate (a carbohydrate present in the walls of algae and seaweed) reduced the activity of a protein in the pancreas that breaks down fats (pancreatic lipase). Lower activity reduces fat breakdown, leading to fewer fats being absorbed after a meal [45].

7 ) Sticks Are Used in Abortion Procedures

Sticks made of Laminaria (a type of kelp) are used to induce birth and perform abortions. Different methods and amounts are used depending on the trimester (inserted into the cervix). The sticks cause the release of prostaglandins, which act as hormones that help initiate womb contractions [46, 47].

Laminaria sticks can mechanically assist in terminating pregnancy from the first to the late second trimester of pregnancy. In one study (longitudinal), 171 late second-trimester abortions were performed using Laminaria (cervical preparation). Only one had serious complications (no contractions during delivery) and 9 required additional safety measures [48, 46, 49].

8) May Treat Herpes

Fucoidan blocked the growth of the herpes simplex virus type 1 (HSV-1) in infected mice. Mice given fucoidan had better survival rates. The treatment improved immune response (innate and adaptive), increasing antibody production [50].

9) May Reduce Blood Clotting and Improve Blood Flow

Fucoidan infusion decreased clotting in bleeding in rats. The rats also had less inflammation around the area of swelling, moved easier, and had better memory retention after fucoidan treatment [51].

Fucoidan supplements prevented blood clotting in mice. The supplements also decreased the activity of blood clot stimulators (platelets and fibrin). In another study, fucoidan injections in mice led to enhanced cell survival and function in tissues with low blood supply (ischemia) [52, 53, 54, 55].

In tissues with low blood supply, fucoidan decreased cell death proteins (including MAPK, JNK, and caspase-3) and harmful compounds (reactive oxygen species) [53].

10) May Protect the Brain

In a study (cell), seaweed extracts (including kelp) protected brain cells from death in cell models of Parkinson’s disease and improved cell survival. It also protected from toxins, helping the cells avoid death (via hydrogen peroxide and caspase-3) [56, 57, 58, 59].

11) Promotes Bone Growth and Strength

In a rabbit model, fucoidan helped create new vessels, essential for communication with bones and bone repair. It also partially improved bone growth in rabbits with defects in skull formation [60].

In human stem cells, fucoidan boosted the development of cells that build bones, called osteoblasts. Fucoidan also increased the growth of new vessels, improving communication with bones [60, 61].

In another cell study, fucoidan increased proteins that promote bone and mineral formation (via BMP-2, osteocalcin, and ALP). Fucoidan given to aged female mice increased bone density and weight suggesting that fucoidan may play a role in treating age-related bone loss [62, 63, 64, 65].

12) May Lower Blood Pressure

Ten protein extracts from a particular sea kelp (wakame) were given to rats with high blood pressure. Of the 10 extracts, 4 experienced decreased blood pressure after both a single dose and routine use [66].

In a cell study, 5 organic brown seaweed (kelp) extracts blocked an important enzyme that may contribute to high blood pressure (Angiotensin-converting Enzyme, ACE). This enzyme is often a target for blood pressure-lowering drugs [67, 68].

13) May Protect from Heart Disease

A 1% or 5% fucoidan (from kelp) diet reduced fat in mice that were fed a high-fat diet over 12 weeks. Kelp reduced the weight of liver and fat tissue, glucose, and fats (cholesterol and fatty acids) in blood. It increased the activity of a protein that breaks down fatty acids (lipoprotein lipase), dissolving the plaque in arteries [69].

14) Is an Antioxidant

The antioxidant properties of fucoidan (from kelp) were confirmed in a cell study that tested its 2 major components, sulfate and fucose. Fucoidan showed antioxidant effects and has the potential to be used as a natural antioxidant [7].

Side Effects & Precautions

1) The Dangers of Excess Iodine in Kelp

A 45-year-old woman with no history of thyroid disease experienced an extended period of thyroid hyperactivity (hyperthyroidism) shortly after beginning a kelp-containing diet. This later developed into low thyroid activity (hypothyroidism), and this thyroid imbalance was caused by the excess iodine in the kelp and seaweed [70, 71, 72, R, 73].

A 39-year-old woman presented with a case of hyperthyroidism after drinking a kelp-containing herbal tea. The tea consumption led to the formation of a goiter, an abnormal enlargement of the thyroid gland [74, R, 71].

Similarly, a 40-year-old woman developed liver damage (hepatotoxicity) after drinking a herbal tea that contained kelp 3 times a day over 2 months. From the excessive iodine, the thyroid glands swelled, leading to hypothyroidism and reducing liver function [75, 76, 71]

A 54-year-old woman experienced hair loss worsening, memory loss, fatigue, and nausea due to exceeding the prescribed amount of kelp supplements. This caused iodine toxicity, impairing thyroid function, and possible arsenic poisoning (present in the patient’s urine) that caused the symptoms [77, R, 71].

2) Kelp Plants Carry the Risk of Heavy Metal Poisoning

Dried seaweed may have high heavy metal content, such as cadmium (Cd). Cadmium can cause toxicity in the body [78].

Levels of other toxic heavy metals, such as arsenic, lead, aluminum, and mercury in Korean seaweed were determined to be very low and are not a health threat [79, 80, 81].

Still, another cellular study (initiated in response to the case of severe side effects) found detectable arsenic levels in 8 out of 9 tested kelp supplements. Levels of arsenic were higher than the FDA tolerance level for certain food products. None informed of possible arsenic contamination [82].

Kelp supplements have been linked to autoimmune disorders that cause red blood cells and blood clotting factors to become defective and attacked by the body’s immune system due to the possible presence of toxic metal (arsenic) [83, 84, 85, 86].

3) Food Labeling

A UK-based study examining the accuracy of food labeling on edible seaweed and algae products surveyed 224 products, and only 10% of them contained information regarding iodine content. Of these, 26 were deemed to potentially lead to iodine intake above the accepted level [87].

4) Laminaria Sticks Can Cause Allergic Reactions in Abortion Procedures

Two women experienced anaphylactic shock, an extremely severe and possibly fatal allergic reaction when Laminaria (a type of kelp) sticks were used to terminate a pregnancy. The reaction included breathing difficulty, nausea, and dangerously low blood pressure. Previous laminaria tent procedures possibly caused this sensitivity [88].

Drug Interactions

As a huge source of iodine, kelp supplements may interfere with thyroid replacement therapies. Excessive amounts of iodine, similar to deficiencies, can alter thyroid hormones released and impair overall thyroid function [89, 71, 90, 91].

Limitations and Caveats

Laminaria sticks can cause infections and allergies. Better methods for inducing abortion or delivery have been found. Laminaria doesn’t reduce the time taken for the procedure in comparison to other methods in use [46, 92, 93, 94].

Supplementing with Kelp


The FDA recommended dosage for daily intake of iodine to 225 μg daily. One gram of powdered kelp contains approximately 200 μg of iodine. Certain kelp-based supplements contain that in one tablet. Never exceed this recommended dosage without consultation. Each approach is different, and in one study, hypothyroidism was treated in patients with between 200 and 400 μg of iodine [77, 95].

Natural Sources/Forms of Supplementation

Kelp is a form of large brown sea algae. Different kelp supplements exist with varying amounts of proteins and other nutrients. In nature, different kelp species (such as Laminaria digitata, Laminaria Hyperborea, Saccharina latissima, Alaria esculenta) that carry more proteins may contain less long-chain carbohydrates (such as fucoidan), and vice-versa [96, 87].

You can take kelp as food, pill, powder, or tincture. Different types of kelp are used, including winged kelp, laminarin, and fingered tangle. Each species varies in iodine levels and nutrients, so the supplement strength and risk will also vary [87, 2, 74, 15].

Genetics Related to Kelp Metabolism

People in some regions of the world may digest large-chain carbohydrates present in seaweed more easily than others. In Japanese society, where diets include more marine algae, a gut bacterium for seaweed digestion developed that is not present in Americans. It originates from a marine bacterium (via gene transfer) living on the surface of sea algae species [96].

User Experiences

Users state that kelp is an effective agent for weight loss and an essential ingredient in energy-boosting juices. Additionally, users with histories of thyroid issues state that the source of iodine present in kelp and its supplements work better than previously prescribed iodine pills, even improving metabolism.

Certain kelp supplement users complain of gaining weight and experiencing depression after long periods of use. Some even complain of developing the dependency on the supplements for thyroid function, due to the iodine imbalance it created. Others complain of excessive sweating and mucus formation after taking kelp-based supplements.

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