Spirulina is a genus of blue-green algae used as a nutritional supplement. Blue-green algae, which are microscopic fresh-water organisms, are also known as cyanobacteria.

Their color is derived from the green pigment of chlorophyll, and the blue from a protein called phycocyanin. The species most commonly recommended for use as a nutritional supplement are Spirulina maxima and Spirulina platensis.

These occur naturally in warm, alkaline, salty, brackish lakes, but are also commonly grown by aquaculture and harvested for commercial use. Spirulina contains many nutrients, including B vitamins, beta-carotene, gamma-linolenic acid, iron, calcium, magnesium, manganese, potassium, selenium, zinc, bioflavonoids, and protein.

Spirulina is about 65% protein by composition. These proteins are complete, in that they contain all essential amino acids, plus some nonessential ones.

In that regard, it is similar to animal protein, but does not contain saturated fats, or residues of hormones or antibiotics that are in some meats. Since spirulina is normally taken in small amounts, the quantity of dietary protein supplied for the average reasonably well-nourished person would not be significant.

However, it is a good source of trace minerals, some vitamins, bioflavonoids, and other phytochemicals. It also has high digestibility and bioavailability of nutrients.

General use

Spirulina has been used as a source of protein and nutrients, particularly beta-carotene, by the World Health Organization (WHO) to feed malnourished Indian children. The program resulted in a decrease of a type of blindness that results from inadequate dietary vitamin A. The dose used in this year-long study was 1 gram per day.

There is a high vitamin B12 content in spirulina. For this reason, it has often been recommended as a supplemental source of the vitamin for vegans and other strict vegetarians, who are unlikely to have adequate dietary vitamin B12.

Unfortunately, spirulina is not an effective source of the usable vitamin. Much of the vitamin B12 is in the form of analogs that are unusable for humans, and may even block the active forms of vitamin B12 consumed from other sources.

Gamma linolenic acid (GLA) is present in significant amounts in a small percent of spirulina species. This essential fatty acid can be used in the body to form products that are anti-inflammatory and antiproliferative.

Spirulina shot
Spirulina shot

It is potentially useful for individuals with rheumatoid arthritis and diabetic neuropathy. It may also play a role in lowering plasma triglycerides and increasing HDL cholesterol.

Spirulina is a good source of available iron and zinc. A study done in rats found that those consuming spirulina had equivalent or better absorption than those given a ferrous sulfate iron supplement.

A small human study of iron-deficient women had good response to iron supplementation with spirulina, although the amounts used were large (4 grams after each meal). Similarly, a study of zinc deficient children found that those taking spirulina had a superior response to those taking zinc sulfate, and had fewer side effects.

In addition to serving as a source of nutrients itself, spirulina has been used in the manufacture of fermented dairy products to guarantee the survival of the bacteria used to ferment the milk.

A stronger immune system is one claim made by boosters of spirulina. A number of animal studies appear to support stimulation of both antibody and cellular types of immunity.

Immune function was markedly improved in children living in the areas surrounding Chernobyl. The measurements were made after 45 days, with each child consuming 5 grams of spirulina per day.

The growth of beneficial intestinal bacteria, including Lactobacillus, appears to be stimulated by the consumption of spirulina, based on a study of rats who consumed it as 5% of their diets. The absorption of vitamin B1 was also improved.

Cholesterol, serum lipids, and low-density lipoprotein (LDL) cholesterol may be lowered by a small but significant percentage by the consumption of spirulina. One study group of men with high cholesterol took 4.2 grams per day of spirulina, and experienced a 4.5% decrease in cholesterol after one month.

Spirulina is also thought to be helpful in the treatment of oral leukoplakia, a precancerous condition that is manifested as white patches in the mouth. It improves experimentally induced oral carcinoma (cancer in the mouth) as supported by studies done in animals.

The evidence for the ability of spirulina to promote weight loss is not very strong. Results have been mixed, and the phenylalanine content does not appear to be an appetite suppressant as is sometimes claimed. Whether other components of the algae are beneficial for weight loss is uncertain and unproven.

Spirulina has been recommended to alleviate the symptoms of attention-deficit hyperactivity disorder (ADHD), although evidence for this indication is lacking.

Spirulina has the highest concentration of evercetin found in a natural source. Evercetin is a potent antioxidant and anti-inflammatory compound that can be used to alleviate the symptoms of sinusitis and asthma.

Phycocyanin, the protein that gives spirulina its blue color, has also been shown to relieve inflammation associated with arthritis and various allergies.

One recommended dose is 3–5 grams per day, but the amount used may depend on the product, the individual using it, and the indication for which it is being taken.


Spirulina supplements are available in powder, flake, capsule, and tablet form. These supplements are generally expensive and have a strong flavor that many people find unpleasant.


Spirulina tablet
Spirulina tablet

Because spirulina is sensitive to pollutants in sea water, it can be used as a biosensor to measure the toxicity of a given body of water. Unfortunately, this sensitivity means that spirulina grown in water contaminated with heavy metals can concentrate these toxic substances.

Mercury levels are of particular concern. Infectious organisms may also be present and contaminate harvested algae, so reputable sources of spirulina should be used.

Phenylketonurics should avoid spirulina due to the potential content of phenylalanine.

A number of varieties of blue-green algae, including Aphanizomenon flos-quae and Anabaena, have been found to sometimes produce toxins that may affect the nervous system or the liver.

Side effects

The potential side effects of spirulina are primarily gastrointestinal, and include diarrhea, nausea, and vomiting. Allergic reactions occur rarely, but can cause insomnia and anxiety.


No interactions of spirulina with foods, conventional medications, or herbs have been documented as of 2002.