Spirulina

Spirulina is the common name for a supplement produced from the dried biomass of filamentous cyanobacteria, photosynthetic microorganisms popularly known as blue-green algae. The main species belong to the genus Arthrospira, principally Arthrospira platensis and Arthrospira maxima, which some recent classifications place in the genus Limnospira. It is not a plant or a true alga but a bacterium, and it is grown commercially in ponds, then harvested, dried, and pressed into powder or tablets.

Spirulina has been eaten for centuries. The Aztecs harvested it from Lake Texcoco in Mexico, and communities around Lake Chad in Africa have long collected a dried cake of it called dihe. Nutritionally it is notable for its high protein content, at well over half its dry weight, along with B vitamins, iron, and other minerals, and the characteristic blue pigment phycocyanin. A common caveat is that the vitamin B12 it contains is largely a biologically inactive form, so it is not a reliable source of that vitamin.

Spirulina is marketed for a broad range of health benefits, but the overall evidence is limited, and health authorities have generally concluded that it cannot be recommended for any specific medical condition ^[1]. The best-supported findings come from cardiometabolic research. Meta-analyses of randomized trials have reported that spirulina supplementation can modestly lower total and LDL cholesterol and triglycerides while raising HDL cholesterol ^[1], and other pooled analyses have found small reductions in body weight and waist circumference, particularly in people with obesity and with longer use ^[2][3]. These effects are generally small, and the underlying studies are often of modest size and quality.

As a supplement, spirulina is not tightly regulated as a medicine, and quality varies between products. Pure, uncontaminated spirulina is generally regarded as safe, but batches can be contaminated with microcystins, toxins produced by other cyanobacteria that can cause digestive upset and, with heavy exposure, liver harm, and some products have been found to carry heavy metals such as lead, mercury, or arsenic. For these reasons third-party testing is emphasized, microcystin limits are set in some countries, and people with the metabolic disorder phenylketonuria are advised to avoid it because of its phenylalanine content.

Generally well tolerated in food amounts. The big risk is contamination; poorly sourced spirulina can carry microcystins, heavy metals, or bacteria, so third-party testing matters. People with autoimmune conditions or phenylketonuria should be cautious.