Spirulina is a blue-green algae that’s widely touted as a superfood (opens in new tab) in the health food and dietary supplement industries. The green powder is known to help lower blood pressure for people with high blood pressure, but there is little scientific evidence that it provides any additional health benefits. Spirulina is generally safe to consume for adults, as long as it’s free of contaminants, such as heavy metals.
Related: Which foods boost the immune system? (opens in new tab)
Where does Spirulina come from?
"Spirulina" sounds so much better than "pond scum," but that's essentially what the popular supplement really is — a type of blue-green algae (opens in new tab) that grows naturally in oceans and salty lakes in subtropical climates. The Aztecs (opens in new tab) harvested Spirulina from Lake Texcoco in central Mexico, and it is still harvested from Lake Chad in west-central Africa and turned into dry cakes.
There are several species, but three — Spirulina platensis, Spirulina maxima and Spirulina fusiformis — are the most extensively studied, presumably because of their high nutritional and potential therapeutic values.
Spirulina grows in microscopic spirals (hence its name), which tend to stick together, making it easy to harvest. It has an intense blue-green color, but a relatively mild taste. Aside from supplements, the U.S. Food and Drug Administration (FDA) allows manufacturers to use Spirulina as a color additive in gum (opens in new tab), candy and other packaged foods.
What's in Spirulina?
According to the U.S. Department of Agriculture (opens in new tab), Spirulina contains essential nutrients such as calcium, iron, magnesium, potassium, and sodium. It also contains essential amino acids (compounds that are the building blocks of proteins). Spirulina is also a good source of protein, as it has about the same amount of protein in meat.
But a person would have to take Spirulina supplements all day to come close to the recommended daily amounts of the nutrients it contains, said Heather Mangieri, registered dietitian and owner of Nutrition Checkup in Pittsburgh, Pennsylvania.
"There's lots of foods that, yes, they have a lot of nutrients in them, but we don't necessarily know the bioavailability so we don't know how much of that nutrient you are actually getting," Mangieri said. In other words, it's unclear how much of those healthy nutrients are actually absorbed by the body and not excreted as waste when they're consumed.
Related: Amino acids to zinc: A glossary of nutrition terms (opens in new tab)
In some cases, eating two different foods at once will help the body absorb nutrients better than if the person ate the foods separately, Mangieri said. For example, leucine, an essential amino acid found in tomatoes, is better absorbed by the body if you eat it with oil, she said. Scientists are still studying the bioavailability of nutrients in individual foods, as well as how nutrients work to help prevent disease.
"As a registered dietitian, I highly recommend people get their nutrients from foods in a healthy diet [as opposed to relying on dietary supplements] because nutrients work synergistically, and that increases the bioavailability," Mangieri said.(opens in new tab)
Potential health benefits of Spirulina
Many people promote Spirulina as a treatment for a range of metabolism and heart health issues, including weight loss, diabetes (opens in new tab) and high cholesterol (opens in new tab). It's also been recommended as an aid for various mental and emotional disorders, including anxiety, stress, depression and attention deficit-hyperactivity disorder (ADHD).
However, according to the U.S. National Library of Medicine (opens in new tab), there is not enough scientific evidence to say that Spirulina is truly effective for treating any health conditions. Nonetheless, Spirulina isn't exactly unhealthy either, as its rich in many nutrients, as mentioned above.
Occasionally, Spirulina is touted as having "antioxidant properties." Antioxidants (opens in new tab) are compounds that help combat cell and DNA damage that leads to cancer, heart disease and other chronic diseases. The body makes some antioxidants, and others are found in food.
Despite the presumed benefits of taking extra antioxidants, extensive research has not shown that taking antioxidant supplements lowers cancer risk, according to the National Cancer Institute (opens in new tab). Taking antioxidant supplements likely won't help other diseases such as diabetes, according to a 2011 abstract published in the journal Current Diabetes Reviews (opens in new tab).
Although antioxidant supplements have failed to stave off disease in studies, it may be "that the lack of benefit in clinical studies can be explained by differences in the effects of the tested antioxidants when they are consumed as purified chemicals as opposed to when they are consumed in foods, which contain complex mixtures of antioxidants, vitamins and minerals," according to the National Cancer Institute.
Since Spirulina is considered a food, it remains an open question as to whether dried Spirulina in supplements has antioxidant health benefits.
The one thing Spirulina supplementation may be helpful for is with decreasing high blood pressure. A recent meta-analysis and review found that daily doses of 1-8 grams of Spirulina taken between 2 and 12 weeks at a time resulted in a significant decrease in blood pressure, particularly for patients with diagnosed hypertension. The review was published in the journal Nutrients and analyzed five randomized, controlled clinical trials with a total of 230 patients.(opens in new tab)
Potential health risks of Spirulina
Spirulina supplements are generally considered safe to consume, but they aren't designed to be taken long-term. The U.S. National Library of Medicine recognizes Spirulina as "possibly safe," as long as it's consumed in doses of up to 19 grams for up to 2 months or up to 10 grams for 6 months. Side effects are typically mild and may include nausea, vomiting, diarrhea, headache and dizziness.
Children are typically more sensitive to blue-green algae than adults, and should not consume Spirulina products.
Women who are pregnant or breast-feeding should avoid Spirulina since there is a lack of safety studies in this group. People who have the genetic condition phenylketonuria should also avoid Spirulina, as it may aggravate their condition, according to the U.S. National Library of Medicine. Since there are not enough studies to establish a safe dose range of Spirulina, it is best to consult a doctor and follow instructions on all supplements to avoid unsafe doses.
- Did you know astronauts snack on Spirulina? Learn more from the European Space Agency (opens in new tab).
- The Aztecs were one of the first groups to harvest and consume Spirulina. Read more about how Mexico is reclaiming the ingredient from BBC News.
- Health scientists are examining Spirulina as a potential way to combat malnutrition in some parts of the world. Read more about it in this story from The Guardian.
Additional reporting by Jessie Szalay, Live Science contributor. This article is for informational purposes only and is not meant to offer medical advice.