JUST HOW SPECIAL IS ‘POND SCUM’?
Its promoters claim spirulina, the dried version of blue-green algae, is a cure-all
Some unflatteringly call it “pond scum.” But to its promoters, it is a “miracle nutrient.” Scientifically, spirulina is the dried version of a simple form of blue-green algae, more specifically classified as “cyanobacteria.” Algae are organisms mostly found in aquatic environments that share a common feature, the ability to photosynthesize. That means they contain chlorophyll, a molecule that can absorb sunlight and use that energy to convert water and carbon dioxide into carbohydrates and oxygen. Algae are critical to life, producing roughly 50 per cent of the oxygen in the atmosphere. Although they resemble plants, they are distinct entities since they lack true roots, stems and leaves. They can be single-celled cyanobacteria, more complex “picoplankton,” measured in millionths of a metre, or giant kelp that can grow up to 60 metres.
The cells of some cyanobacteria are spiral-shaped, hence the term “spirulina” from the Latin “spiru” for tiny spiral. On the surface of some lakes or ponds, these bacteria aggregate into a mass that can be scooped up and dried, forming a greenish edible cake. Historically, spirulina is known to have been consumed by the Aztecs, who even offered it to the Spanish conquistadores.
Today, these cyanobacteria are cultured in ponds for conversion into a powder that is sold as a nutritional supplement, often with exuberant claims. The powder is about 60 to 70 per cent protein and contains a variety of vitamins and minerals. On a gram per gram basis it is very nutritious, but at the doses recommended, usually in the range of one to four grams, neither the protein content nor the other nutrients make a significant contribution to the diet. Promoted as a source of calcium, spirulina actually contains only about five mg in a four-gram serving. By comparison, a cup of broccoli has 45 mgs and will also deliver other nutrients comparable to spirulina at a fraction of the cost. Sometimes spirulina is promoted as a source of vitamin B12 for vegans, but the form of B12 that cyanobacteria contain is biologically inactive in humans.
Spirulina is likely to be safe, but since it is regulated as a food, not as a drug, there is no verification that a product contains what the label declares. Some varieties of blue-green algae produce highly toxic compounds called microcystins that can lead to vomiting, rapid heartbeat, nausea and liver damage. These algae can grow alongside spirulina in natural environments and pose a risk of contamination. However, most spirulina destined for supplements is grown in a controlled environment and is hopefully tested for toxins. Various human illnesses have been reported as a consequence of contact with toxic cyanobacteria through recreational activities such as canoeing or swimming through blooms of blue-green algae.
Now for the hype. Some promoters claim that spirulina may prevent, treat or cure conditions such as hypertension, diabetes, depression, high cholesterol, cancer and even “Lou Gehrig ’s disease.” The weasel word “may” does come in handy. Spirulina is also said to boost the immune system and improve liver and kidney function. There are also meaningless assertions about energizing and detoxifying the body and purifying the blood.
When challenged to provide evidence for the claims, promoters point at studies carried out in cell cultures or in animals. Spirulina extracts have shown some anti-inflammatory effects in cells and a reduced risk of atherosclerosis in rabbits fed a high cholesterol diet. A few smallscale human studies have shown a beneficial effect in controlling blood glucose levels in diabetics at a dose of two grams a day, and improved exercise performance in athletes at six grams a day. One study showed that supplements slightly increased hemoglobin levels in senior citizens. None of these studies are compelling.
The major concern is when studies that have little relevance to humans are dredged out to support claims of treating serious conditions. These usually focus on phycocyanin, the blue colourant in spirulina that in laboratory studies can be shown to have antioxidant and anticancer cell growth effects. There is nothing special about this, as numerous compounds isolated from various life forms show such effects in the lab but fail in clinical trials in people.
Where spirulina has been shown to have a practical use is as a supplier of blue food colouring. The green in blue-green algae is due to chlorophyll, while phycocyanin is responsible for the blue tinge. The latter can be extracted to yield a vivid blue that can be used as a “natural” alternative to artificial colours such as Brilliant Blue (F, D & C No. 1). It can be used in ice cream, puddings, yogurts and confectionary. When Nestle pledged to remove artificial colours from Smarties in 2006, there was no alternative to Brilliant Blue, and for about two years there were no blue Smarties. Then researchers hit upon spirulina extract and consumers who had been feeling blue were happy again. So far, surprisingly, nobody has claimed that blue Smarties offer a health benefit due to their phycocyanin content. We’re waiting.
joe.schwarcz@mcgill.ca Joe Schwarcz is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.