Seaweed Benefits: All About the Iodine and Iron
In Asia, many people eat seaweed daily. It’s not as common in Western countries, where it’s most often found in sushi. It can also be used in various dishes, including soups, salads, stews, and smoothies. Eating seaweed may benefit your thyroid, blood sugar, heart, and more. Seaweed has many different flavors depending on how it’s prepared. Common varieties are often described as salty, umami (earthy), fishy, or briny. The texture may be anywhere from rubbery to crispy. This article discusses the health benefits of seaweed, possible risks and side effects, and how to eat it safely.
8 Seaweed Benefits You Might Not Expect
Much of what experts know about seaweed benefits comes from laboratory or animal studies. However, human trials are increasing, and seaweed’s long history as part of a human diet means it’s well-established as safe for regular consumption. Evidence shows that seaweed benefits your blood pressure, weight, cholesterol, and more.
Diabetes/Blood Sugar Control
Research found seaweed may help with diabetes and blood sugar regulation. In one study of brown seaweed, participants saw a significant improvement in hemoglobin A1c (HbA1c) tests, an essential measurement of blood sugar control. Multiple reviews also report that seaweed positively impacts blood sugar levels, especially in people with type 2 diabetes. The effect appears to happen soon after consumption. However, the longer-term impact is unknown.
Blood Pressure Regulation
High blood pressure (hypertension) is a significant risk factor for heart disease and stroke. Research suggests seaweed may help lower blood pressure, possibly due to how your body processes sodium. Excess sodium consumption is linked to high blood pressure. Alginate and other compounds bind to sodium and will excrete it, which prevents the body from absorbing the sodium and, in turn, will not have the effect on blood pressure that sodium normally does. Other components in seaweed may have an effect similar to blood pressure medications called angiotensin converting enzyme (ACE) inhibitors. Both the medications and seaweed inhibit the chemical known as angiotensin converting enzyme.
Weight Control/BMI
In some research, seaweed appears to positively affect weight and waist circumference and has a slight impact on body mass index (BMI), which are risk factors for type 2 diabetes, heart disease, and premature death. Consumption is needed to be fairly high, more than 4 grams (g) daily. Results also haven’t been consistent across studies; in one, the effects were seen only in males.
Cholesterol/Blood Lipids
High cholesterol levels and other blood lipids increase your risk of heart and metabolic diseases. Seaweed is a high-fiber food; high-fiber diets are a known way to lower these levels.
Studies are mixed as to seaweed’s actual effect on human lipid levels. Some research has found that seaweed consumption may lower levels of triglycerides (a fat in the blood) and low-density lipoprotein (LDL) cholesterol (“bad” cholesterol) and increase high-density lipoprotein (HDL) cholesterol (“good” cholesterol). However, another study reported increased triglycerides after four weeks of a high-seaweed diet.
Other Benefits
Possible seaweed benefits with less evidence backing them include:
- Appetite: Some research suggests eating seaweed may help you feel full faster, but the evidence is weak.
- Thyroid function: High iodine content in seaweed may support thyroid health, but studies suggest it may raise levels too much and harm thyroid function.
- Oxidative stress: Many diseases are linked to oxidative stress, and antioxidants in brown seaweed appear to help alleviate oxidative stress.
- Blood mineral levels: Despite seaweed’s high levels of calcium and other minerals, studies have failed to show that the food can increase mineral levels in your blood.
Nutrition Facts for Single Serving of Seaweed
Nutritionally, seaweed is similar to many vegetables. It’s low in sugar and fat but packed with nutrients.
If you’re not accustomed to eating seaweed, you may want to start with small amounts of dried seaweed and increase it as you get used to the flavor or find ways you like it. Even a single tablespoon offers some nutritional benefits.
| Nutritional Content, Dried Spirulina Seaweed in Milligrams (mg), Grams (g), Micrograms (mcg), and International Units (IU) | ||
|---|---|---|
| 1 Tbsp | 1 Cup | |
| Fiber | 0.25 g | 4.03 g |
| Calcium | 8.4 mg | 134 mg |
| Iron | 2 mg | 31.9 mg |
| Magnesium | 13.6 mg | 218 mg |
| Potassium | 95.2 mg | 1,520 mg |
| Sodium | 73.5 mg | 1,180 mg |
| Vitamin C | 0.707 mg | 11.3 mg |
| Folate | 6.58 mcg | 105 mcg |
| Vitamin A | 39.9 IU | 638 IU |
| Fatty Acids | 0.185 g | 2.97 g |
Iodine levels vary greatly by seaweed type. Nori, the most common type, has 58 mcg per tablespoon, or 928 mcg per cup.
Comparing Fresh, Roasted, and Dried Seaweed
You can eat fresh seaweed right out of the ocean. Fresh seaweed is commonly used in seaweed salads.
Most commercially available seaweed is dried through roasting. This includes the variety called nori, which is the standard sushi seaweed. Nori comes in thin, dry strips often wrapped around a sushi roll.
How Much Is Too Much Seaweed?
While seaweed may offer some health benefits, eating too much of it could become a problem. This is due to its iodine and heavy metal content.
Iodine
Most people in the United States and other developed countries get enough iodine in their diets. Iodine intake over 1,100 mcg is considered dangerous. If you include seaweed in your diet, keep your total iodine consumption under that level.
Heavy Metals
Heavy metals can contaminate seaweed in the water where it grows. Washing and cooking may not remove them effectively. Heavy metals such as mercury can impair thyroid function. Your thyroid health may take a double hit from large amounts of seaweed. While heavy metals in seaweed may be relatively low, regularly eating it can lead to heavy metal toxicity. One study showed healthy adults who ate large amounts of seaweed had elevated levels of arsenic.
Potential Side Effects
Side effects of excess dietary iodine include:
- Burning in the mouth, throat, and stomach
- Coma
- Diarrhea
- Fever
- Nausea and vomiting
- Stomach pain
- Weak pulse
Symptoms of hypothyroidism (low thyroid function), which may result from eating too much iodine, can be:
- Cold intolerance
- Depression
- Dry skin
- Fatigue
- Infertility
- Irregular or heavy menstrual periods
- Pain in the joints and muscles
- Slow heart rate
- Thinning hair
- Weight gain
Heavy metals may cause the following side effects:
- Cancer
- Congenital disabilities
- Damage to blood vessels
- Digestive problems
- Immune system dysfunction
- Kidney dysfunction
- Nervous system disorders
- Skin lesions
Research suggests eating seaweed once or twice a week is likely safe. Use caution when consuming more than that. Speak with a healthcare provider before consuming seaweed if you are concerned.
Sourcing Reputable Seaweed
Many types of seaweed are available online and in stores, especially in Asian markets. These products are not required to list iodine or heavy metal content.
However, most commercial seaweed is farmed, not harvested from the sea, which should reduce the risk of heavy metal contamination. You may learn the seaweed’s source from the label or the company’s website.
When buying dried seaweed, be sure it’s in a sealed, air-tight container. It shouldn’t be especially crumbly or look gray. Properly packaged dry seaweed should last for a long time.
Summary
Seaweed can be used in sushi, soups, salads, and smoothies. Although more research is needed, some evidence shows seaweed may benefit your thyroid function, blood sugar, heart, and more. Seaweed can be eaten raw, or it can be dried or roasted.
While seaweed is packed with nutrients, too much may be a problem due to the iodine and heavy metal content. Too much iodine in your diet can impact thyroid function, leading to hypothyroidism. Speak to a healthcare provider if you’re concerned before consuming seaweed.
