It’s been touted as a “superfood” that can eliminate world hunger by the United Nations , as a potential food source for space travelers by NASA , and as a phytonutrient with “amazing” abilities to lower blood pressure, reduce cholesterol, boost energy, improve HIV/AIDS, detoxify heavy metals, and prevent cancer. It’s called spirulina, a form of blue-green algae that has been used as food since the times of the Aztecs.
But how much of the health claims are supported by scientific evidence? Well, let’s examine what has been learned about spirulina so far.
What Is Spirulina?
Spirulina represents a biomass of cyanobacteria (often referred to as blue-green algae) that can be consumed by humans and other animals.
There are two species: Arthrospira platensis and A. maxima. Calling them “algae” is really a misnomer, as algae are considered eukaryotes (any organism whose cells have a cell nucleus and other organelles enclosed within membranes). Instead, spirulina is a form of cyanobacteria - a kind of bacteria that obtain their energy through photosynthesis.
And, like plants, they can produce oxygen. Interestingly, cyanobacteria are thought to have played a major role in the Great Oxygenation Event  of Earth which created an oxygen atmosphere and dramatically changed the composition of the Earth's life forms.
Spirulina grows naturally in salty lakes in subtropical climates. It likes warm, alkaline water. Natural habitats include the Hawaii, large fresh water lakes, including Lake Texcoco in Mexico, Lake Chad in Africa, and Lake Titicaca in South America. It can also be “farmed” in tanks under controlled conditions.
Spirulina is reported as a food source for the Aztecs and other Mesoamericans until the 16th century. The Aztecs called it “tecuitlatl.” The Kanembu tribe harvested what they called “dihé”, which they used to make broths for meals.
Spirulina is high in protein - composing nearly 60-70% of its dry weight. Other foods considered “good protein sources” only contain about 35% protein. Spirulina provides a complete complement of protein containing all the nine essential amino acids (the building blocks of proteins that our bodies cannot make itself and must be obtained through the diet).
Although the amount of methionine and cysteine (2 essential amino acids) is lower in spirulina than in egg or milk, it is much higher than in almost any vegetable source (including legumes and soy).  The protein in spirulina is also well absorbed.
Spirulina contains 5-10% fats, and is a good source of gamma-linolenic, linoleic, and oleic acids. Gamma-linolenic acid makes up 20% of the fatty acids and is a precursor of prostaglandin, leukotrienes and thromboxanes which are mediators of inflammation and immune responses.
Spirulina is a good source of vitamins. It contains vitamins B-1 (thiamine), B-2 (riboflavin), B-3(nicotinamide), B-6 (pyridoxine), B-9 (folic acid), vitamin C, vitamin D, and vitamin E. It also is a good source of beta-carotene which is converted into vitamin A. Although there are claims that spirulina is very high in vitamin B-12, scientists have found most of the vitamin B12 is in an inactive form  which is not “bioavailable” for humans.
In terms of minerals, spirulina is a good source of iron, with one tbsp containing 11% of the recommended daily allowance (RDA). It's calcium and phosphorus content is comparable to that of milk, if you look at the mg of calcium per 100 grams (3.5 oz.). However, the recommended serving size of spirulina is only 1 tsp-1 tbsp (½ oz) or 5-15 grams/day.
Most spirulina available for purchase is grown in large vats or man-made ponds of highly alkaline water. It also contains specific “ingredients” such as nitrous and carbon dioxide, citric acid, magnesium sulfate, calcium chloride and urea. The biomass is then harvested, strained, and dried. It is then made into a powder or pressed into tablets to be sold to consumers.
How to eat spirulina? If you prefer to try the powdered form over the tablets, you could stir a small spoonful into a glass of water but expect it to taste something like pond scum. It’s probably better to add it to juice or a smoothie. It can also be added to flour and baked into brownies or other baked goods. But bon appétit warns: “Just a small amount of deeply-pigmented spirulina will change the color of your drink into a deep blue-green, almost black. (Keep a glass of water handy to prevent a blue-green teeth situation.)”
Although gram for gram, spirulina is one of the most nutritious foods, it is probably one of the most expensive. It costs up to thirty times as much as dairy or meat protein per gram. In can be more economical in underdeveloped areas where “farmers” can set up small scale spirulina farms under the auspices of the United Nation’s Intergovernmental Institution for the use of Micro-algae Spirulina Against Malnutrition (IIMSAM).
Is There Any Research?
As of March 2018, the biomedical literature (PubMed.gov) contains 1623 articles about spirulina dating back to 1967. Most of these research studies involve experiments with laboratory animals or “test tubes” (in vitro studies). Of all the articles citing spirulina, only 49 studies appear to involve human subjects.
Turning to the U.S. government’s database of clinical research trials (ClinicalTrials.gov), spirulina yielded 17 studies as of March 22, 2018. Only two trials have been done in the United States. The other trials were done in Poland, Cameroon, Bangladesh, Egypt, Mexico, and the Netherlands. These studies involve a wide variety of conditions including obesity, insulin resistance, HIV/AIDS, thalassemia, cardiovascular disease, and periodontitis.
By comparison, another "green" health trend celery juice - all the rage on Instagram - has only a handful of published articles and no clinical trials.
Does Spirulina Help Sinus Issues?
The term “sinus issues” is a rather non-descript term, and as such, there are no specific studies found in PubMed linking spirulina and “sinus”. However, allergic rhinitis (nasal allergies) is an important contributing factor to problems in the sinuses. There are a few (less than a handful) of studies that look at the effect of spirulina on allergic rhinitis.
Chen et al  looked at rats sensitized to the protein ovalbumin. Half of a group were treated with Spirulina platensis (SPP) for an undisclosed amount of time (the original article is in Chinese, and only an abstract is available in English). After treatment, the rats were evaluated for changes in behavior and for changes in the nasal mucosa when examined under a microscope.
The mucosa was also examined for mast cell degranulation. Mast cells are white blood cells that contain granules of histamine which are released when exposed to an allergen. Histamine release leads to all those nasty symptoms of allergies- sneezing, tearing of the eyes, itchiness, and watery nasal discharge.
Lastly, the levels of serum histamine and IgE were obtained before and after treatment. IgE is an immunoglobulin associated with allergic reactions. They found that there was significant improvement of behavior, lower numbers of mast cells and mast cell degranulation, and lower levels of histamine and IgE in rats who had received SPP over controls.
Mao, Vande Water and Gershwin  conducted a randomized double-blind study where allergic patients were fed either placebo or 1 or 2g of spirulina daily for 12 weeks. Blood mononuclear cells were collected before and after treatment. The samples were stimulated with phytohemagglutinin (PHA), a substance that causes clumping of red or white blood cells. Those treated with 2g of spirulina had significantly suppressed secretion of the pro-inflammatory cytokine IL-4 in response to PHA. They suggest that their results “demonstrate the protective effects of Spirulina towards allergic rhinitis.”
Cingi et al  looked at 129 adults (aged 19-49) with a history of allergic rhinitis. They were divided into two groups, one of which consumed 2g/day of spirulina or a placebo for 6 months. They were not permitted to take any anti-allergy or rhinitis medication during the study period.
They were examined by a physician and assessed for symptoms before and after treatment and participants recorded a weekly diary of allergy symptoms. Those treated with spirulina has a significant improvement in subjective symptoms such as reduced frequency of nasal discharge, nasal congestion, and nasal itching and sneezing.
The most recent study, by Appel et al  looked at two commercial preparations, Immulina® and immunLoges® which contain a high-molecular-weight polysaccharide extract from spirulina. The researchers looked at whether these preparations have an inhibitory effect on an induced allergic reaction and on histamine release of mast cells.
Their findings showed that Immulina® and immunLoges® inhibited the IgE-antigen complex-induced production of TNF-α (tumor necrosis factor alpha- a cell signaling protein that is released in an allergic reaction), IL-4, leukotrienes and histamine. Their results suggest that Immulina® and immunLoges® exhibit anti-inflammatory properties and inhibited the release of histamine from mast cells.
Some evidence suggests that spirulina can be helpful in the treatment and/or prevention of allergic symptoms. However large-scale studies are needed to assess whether these findings will hold up.
Does It Speed Up Weight Loss?
There are only three papers in the scientific literature that look at the role of spirulina in weight loss. The first, by Balasubramanian et al  looked at whether spirulina could decrease the weight gained by rats fed a high fat diet. The amount of weight was significantly decreased by the co-administration of 1 gram of spirulina in the diet.
Zeinalian et al  studied 64 healthy obese individuals. Half received 1 gram of spirulina capsules and the other half placebo for a period of 12 weeks. The body weight and body mass index (BMI) were significantly reduced in the treated vs. untreated group. The additional weight loss was about 2 pounds.
The treated group also had a significant decrease in appetite which could, in itself, account for the weight loss. It is unclear to me whether the there is something specific in spirulina that decreases the appetite or whether it is because of an overall increase in dietary protein.
Lastly, Miczke et al  studies 40 patients with high blood pressure (without evidence of cardiovascular disease) who received 2 grams spirulina or placebo for 3 months. They found no change in body mass index or weight in either the spirulina or placebo group.
There is little consistent evidence at this point to say that spirulina has an effect on weight loss.
Does It Boost Energy?
A search of PubMed revealed no studies specifically done to assess whether spirulina boosts energy. Claims that spirulina can boost energy may be based on the idea that it is a good source of B vitamins. It is true that B vitamins—thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid, pyridoxine (B6), B12, biotin, and folate (B9)—are all involved, one way or another, in energy production.
But the vitamins don’t directly provide energy. It’s the macronutrients – proteins, carbohydrates and fats – in our food that provide energy and it comes as calories. In mitochondria (an organelle within each cell), B vitamins help convert dietary energy into ATP (adenosine triphosphate), the form of energy that your body can use in its metabolic processes.
There is no scientific evidence that spirulina can directly boost energy.
Does It Lower the Chance of Stroke?
Stroke is a medical condition in which poor blood flow to the brain results in cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding.
In ischemic stroke the reduction in blood supply leads to a cascade of chemical imbalances which leads to an excess of free radicals, which are oxygen molecules with unpaired electrons. These molecules are unstable (reactive) and can chemically interact with cell components such as DNA, protein, or lipid, stealing their electrons to become stabilized. This can then trigger a chain of free radical reactions, which have the potential to cause considerable damage to brain cells. Unfortunately, resupplying an area of the brain can also lead to the accumulation of reactive oxygen and free radicals.
Studies have shown that antioxidants or free radical-scavenging agents can have a protective effect in experimental stroke. Spirulina has been shown to have a wide range of antioxidants including superoxide dismutase (SOD), beta-carotene, vitamin C, E, selenium, flavonoids and phycocyanins. Therefore, it is reasonable to ask whether spirulina can be neuroprotective and reduced the risk of stroke.
Thaakur and Sravanthi  looked at the effect of spirulina in rats who has a major blood vessel in their brains (the middle cerebral artery- MCA) temporarily blocked. Rats who received a diet supplemented with spirulina for a week prior to the procedure showed a significantly decreased amount of abnormalities in the brain tissue and less neurologic deficits than control subjects. Based on the pre- and post-procedure levels of certain brain chemicals, they postulated that the protective effects of spirulina “may be due to its antioxidant property”.
Wang et al  looked at rats fed diets supplemented with blueberry, spinach, or spirulina or a control diet. After 4 weeks, the animals underwent temporary MCA blockage. They found that “animals which received blueberry, spinach, or spirulina enriched diets has a significant reduction in the volume of infarction (brain cell death) in the cerebral cortex and an increase in post-stroke locomotor activity.”
The researchers also measured the amount of caspase-3, an enzyme which is thought to play a part in apoptosis- a process of programmed cell death. Animals pretreated with spirulina had the least cerebral infarction and caspase-3 activity. It should be noted that, although the functional recovery of movement was significant, some degree of deficit remained, compared to the control animals who did not undergo the procedure.
Myelin is a fatty substance that surrounds and protects the nerve fibers in the central nervous system. It allows for the rapid conduction of electrical impulses along nerve fibers and serves to maintain function with nourishing and repair/regrowth support. A recent review by Penton-Rol et al  looked at two specific biliproteins found in spirulina: C-Phycocyanin (C-PC) and Phycocyanobilin (PCB).
Based on a review of the current scientific literature as well as their own research using rat models, they believe these two biliproteins play an important role in the remyelinating of nerve cells after stroke. They found, using electron microscopy, that the cerebral cortex from ischemic rats revealed a potent remyelination action of PCB treatment after stroke.
There are some promising results in in vitro and in vivo experiments looking at a neuroprotective role of spirulina. There is, at present, no scientific evidence that these kinds of results will be seen in humans. Large scale, double-blind studies are needed.
Does It Reduce Cholesterol? Lower Blood Pressure?
High blood cholesterol (hypercholesterolemia) is a condition that causes the levels of certain bad fats, or lipids, to be too high in the blood. This condition is usually caused by lifestyle factors, such as diet, in combination with the genes that you inherit from your parents. Two kinds of lipoproteins carry cholesterol throughout your body: low-density lipoproteins (LDL) and high-density lipoproteins (HDL). Having healthy levels of both types of lipoproteins is important.
LDL cholesterol sometimes is called “bad” cholesterol. A high LDL level leads to a buildup of cholesterol in your arteries. HDL cholesterol sometimes is called “good” cholesterol. This is because it carries cholesterol from other parts of your body back to your liver. Your liver removes the cholesterol from your body.
In 2005, Nagaoka et al  examined the effect of spirulina, in addition to the biliprotein C-phycocyanin (C-PC) on the levels of cholesterol in rats fed a high-cholesterol diet compared to control animals fed casein (cow protein). They found significantly lower total cholesterol and LDL + VLDL (very low-density cholesterol) in the spirulina group. The HDL levels were increased in both the spirulina and C-PC groups.
In 2009, Cheong et al  looked at rabbits with hypercholesterolemia due to a high cholesterol diet (HCD). These rabbits were fed the HCD along with spirulina for 8 weeks. At the end of this period serum LDL, total cholesterol, and TG (triglycerides) were all significantly lowered compared to controls. Serum HDL was significantly increased in the spirulina rabbits. The authors concluded that spirulina may be beneficial in reducing the risk factors for cardiovascular diseases.
Torres-Duran et al  looked at the effects of spirulina on a group of 36 Mexican men and women (ages 18-65) fed spirulina for 6 weeks. Pre- and post-supplementation blood glucose and serum lipids were compared. They found no significant difference in glucose levels but found significant differences in TAG (triacylglycerols- the form in which fat energy is stored in adipose tissue), total cholesterol, and HDL cholesterol.
The changes in HDL-C and TC were dependent on the concentration of TAG, however decreases in LDL-C were not dependent on TAG levels. The dependence of TC and HDL-C levels on TAG makes these results difficult to interpret.
Seban et al  did a systematic review and meta-analysis of the impact of Spirulina on plasma lipid concentrations in 2015. Out of over 750 published studies identified through a database search of PubMed and Scopus, 51 records were screened. Only 12 articles were assessed for eligibility, and of these only seven   [21-24] [25, 26]were included for review and meta-analysis.
The included studies covered 522 participants who were randomized to spirulina (312) or control (210). They ran between 2 and 12 months in length. Based on these RCTs (randomized controlled trials), spirulina supplementation caused a significant effect in reducing plasma concentrations of total cholesterol, LDL-C and triglycerides (TG), and increasing those of HDL-C. They suggested that the active components responsible for these effects are not completely understood and should be the focus of future studies.
Only two clinical studies looked at the effect of spirulina on blood pressure. Torres-Duran  (see above) also looked at the blood pressures of the participants in their trial before and after supplementation with spirulina for 6 weeks. Participants were instructed not to modify their diet during the experimental period. Only 11% of the patients had normal blood pressure prior to the study.
Forty-four percent were considered to have prehypertension, 31% hypertension stage 1 and 14% hypertension stage 2. Few details are given about how the BP’s were obtained or what was the criteria for blood pressure stages. They report a significant decrease in blood pressure: systolic BP (initial 120±9 to final 109±9) (p<0.001), diastolic BP (initial 85±9 to final 79±8) (p<0.05).
The second study, a randomized double-blind placebo-controlled trial in Poland by Miczke et al  enrolled 40 patients with hypertension who lacked clinical evidence of cardiovascular disease. Half of the patients received 2 grams of Hawaiian spirulina or placebo for 3 months. They looked at pre- and post- weight, body mass index (BMI), diastolic BP, systolic BP and something called a stiffness index (SI).
Arterial stiffness occurs because of biological aging and arteriosclerosis. Inflammation plays a major role in arteriosclerosis development, and consequently it is a major contributor in large arteries stiffening. Arterial stiffness is influenced by structural factors (including the relative amounts of elastin and collagen) and dynamic factors such as arterial tone and the balance of vasodilators and vasoconstrictors produced locally. Miczke used digital plethysmography as an indirect method for determining arterial stiffness. After the three-month period, there was a significant reduction in SBP and SI. Diastolic BP decreased but did not reach a significant level.
If you have high cholesterol, ask your doctor whether you could try Spirulina first before going on prescription medication. If you have high blood pressure, supplementation with spirulina may be helpful, but do not stop taking your prescription medication.
Does It Help Prevent Cancer?
The rationale that ingesting spirulina might help prevent cancer is mostly because it is known to stimulate the immune system and the immune system is an important natural defense against cells that become cancerous.
The only data from humans is an article published more than 20 years ago that asked the question: Can eating 1 gram of Spirulina every day for a year reduce or eliminate precancerous lesions in the mouths of tobacco-chewers in Kerala, India?  This small study did show some positive results but the fact that it has never been replicated or expanded in the subsequent 23 years since publication calls the results into question.
There are a handful of more recent publications that investigated spirulina for the chemoprevention of colon and breast cancer in rats and mice. Saini and Sanyal  showed that a protein, C-phycocyanin, found in spirulina might be able to interfere with tumors’ blood supplies. Ouhtit et al. showed that spirulina might be able to induce programmed cell death in tumor cells.
Spirulina and other cyanobacterial species continue to be “mined” for anti-cancer, drug-like substances.[32, 33] However there is, as yet, no definitive evidence that spirulina can either prevent or treat cancer in humans.
There is very little evidence that spirulina can prevent cancer in humans.
Does It Help Improve HIV/AIDS?
HIV is a virus spread through certain body fluids that attacks the body’s immune system, specifically the CD4 cells, a kind of T cells. These cells help the immune system fight off infections. Untreated, HIV reduces the number of CD4 cells in the body. This damage to the immune system makes it harder and harder for the body to fight off infections and some other diseases. Opportunistic infections or cancers take advantage of a very weak immune system and signal that the person now has AIDS.
Spirulina has been suggested for two different roles in the treatment of HIV/AIDS: (1) as an antiviral, to curtail or slow the progression of the disease, and (2) as a way to improve the nutrition of patients with HIV/AIDS (particularly in underdeveloped nations).
There are a few in vitro studies that look at spirulina’s possible antiviral properties. Hayashi et al  looked at a component of spirulina, calcium spirulan (Ca-Sp). They found that Ca-Sp inhibits the in vitro replication of several enveloped viruses such as Herpes simplex-1, cytomegalovirus, measles and mumps virus, influenza A and HIV.
Ayehunie et al  showed that an extract of spirulina inhibited HIV-1 replication in vitro in human T-cells, blood mononuclear cells and Langerhans cells (dendritic, antigen-presenting immune cells of the skin and mucosa). Unfortunately, only abstracts of both articles are available, so it is difficult to assess the quality of the work.
There are 5 studies that examine the effect of spirulina in clinical trials. Two examine the effect of Spirulina on CD4 cells and viral load on a population in Cameroon, one is a Phase 1 and 2 study of 11 patients in South Carolina, and two looks at the nutritional value of spirulina, one on children with HIV in Burkina Faso and the other on adults from the Central African Republic. Winter et al  looked at the effects of spirulina supplementation on 58 HIV-infected women, prior to starting antiretroviral therapy for a period of 3 months.
They did not observe any benefit of spirulina on the viral load and/or the CD-4 T-cells. They do say that the intervention “seemed to reduce the incidence of concomitant events, as well as opportunistic infections and showed a positive effect on weight stabilization.”
Ngo-Matip et al  looked at 169 HIV infected men and women in Cameroon who had not yet received any antiretroviral treatment. They received spirulina supplementation or standard care and local diet for one year. At 6 months, they found that treated patients had a significant increase in CD4 T-cells and a decrease in viral load.
Teas and Irhimeh  had 5 pretreatment African-American patients from South Carolina participate in a phase I trial of spirulina. Phase 1 trials look for any acute toxic effects, and none were observed after 5 days of treatment. Six additional subjects (5 African-American and 1 Latina) were added begun on spirulina and observed for short- and long-term toxitcities after 3 weeks of treatment. “No significant changes were observed in CBC (blood count), metabolic or lipid panel analysis. CD4 and viral load remained stable over the first 3-month phase II study period.”
Simpore et al  examined the effect of spirulina on 84 HIV-infected and 86 HIV-negative undernourished children in Burkina Faso. The duration of the study was 8 weeks. Researchers measured anthropometric parameters (height, weight, BMI) and blood counts to assess the effectiveness of spirulina supplementation (SP). Treatment with SP shows on average a weight gain of 15 and 25 g/day in HIV-infected and HIV-negative children, respectively. The level of anemia decreased during the study in all children, but recuperation was less efficient among HIV-infected children.
Yamani et al  conducted a placebo-controlled trial of 160 adults from the Central African Republic who had not received antiretrovirals. The treatment group received 10g of spirulina a day in addition to the food supplied to all participants from the World Food Program. Follow-up of the 160 patients at three and six months showed that 16 patients had been lost from follow-up and 16 had died. A significant improvement in the main follow-up criteria, i.e., weight, arm girth, number of infectious episodes, CD4 count, and blood protein level, was observed in both groups.
Spirulina may have some value in the nutritional support of patients with HIV/AIDS. But it is not a substitute for prescription anti-viral medications.
Does It Help Candida?
Candidiasis is a fungal infection caused by yeasts that belong to the genus Candida. There are over 20 species of Candida yeasts that can cause infection in humans, the most common of which is Candida albicans. Candida yeasts normally reside in the intestinal tract and can be found on mucous membranes and skin without causing infection; however, overgrowth of these organisms can cause symptoms to develop. Symptoms of candidiasis vary depending on the area of the body that is infected.
Most of the already sparse data concerning the effect of spirulina on candida has been done in vivo on mice. El-Sheekh et al  were able to prolong the lives by 2 weeks of mice exposed to candida albicans after receiving polysaccharides and phycocyanin derived from spirulina. Soltani et al  fed mice a dose of 800mg/kg of spirulina for four days prior to being injected with Candida albicans. They found that spirulina-treated mice produced more IFNγ and TNFα than control rats.
IFNγ is a kind of interferon which triggers a cellular response to viral and microbial infections. TNFα (tumor necrosis factor alpha) is a cell signaling protein (cytokine) involved in systemic inflammation and is one of the cytokines that make up the acute phase reaction.
Ozdemir et al  looked at various extracts of spirulina to see what effect they have on antimicrobial activity. They tested these extracts on 10 species of bacteria and Candida albicans. One extract (methanol extracted) showed antifungal activity against candida, but it was less than that of nystatin (a pharmaceutical often used to treat candida).
Marangoni et al  evaluated the in vitro antifungal activity of a water extract of spirulina against 22 strains of Candida spp. They found that the extract of spirulina that they used had good antifungal properties. They also looked at whether the dose needed to cause fungal death would harm the main health-promoting bacteria normally present in the vagina (primarily lactobacilli).
Finally, they looked at whether the extract would alter the normal contractility of uterine muscle (tested using guinea pig uterus). They concluded that “the good anti-fungal properties together with the absence of negative effects on the endogenous microbiota and on the spontaneous motility of uterine smooth muscle, could potentially allow the use of this extract as an alternative approach to topical antifungal agents for vulvovaginitis treatment.”
Various extracts of spirulina exhibit antifungal activity primarily in vitro or in laboratory animal (mouse) models. There is no data on whether spirulina might provide any benefit in humans.
Does It Detox Heavy Metals?
Metals can damage certain tissues by causing oxidative stress. Oxidative stress is an imbalance between the production of free radicals and the ability of the body to counteract or detoxify their harmful effects through neutralization by antioxidants. These can be endogenous antioxidants (made by the body) such as reduced glutathione (GSH), superoxide dismutase (SOD) and nitric oxide (NO), or exogenous (supplemented by diet or other means). Metals are also capable of interacting with protein sulfhydryl groups, which interferes with crucial enzymes and key biological properties.
A paper by Martínez-Galero et al  reviewed the pre-clinical literature on the antitoxic effects of spirulina. Twenty-two papers were reviewed with a variety of contaminants including arsenic, cadmium, carbon tetrachloride, fluoride, iron, lead and mercury. All these studies showed, in varying degrees, the protective activity of spirulina, most based on its antioxidant properties.
The only study in humans is by Misbahuddin and Khandker  who did a placebo-controlled double-blind study of 41 patients with chronic arsenic poisoning from Bangladesh. Chronic arsenic poisoning is common in Bangladesh, obtained by drinking water from shallow tubewells contaminated with arsenic. The skin is the first manifestation of arsenic poisoning. It is characterized by areas of hyperpigmentation on the upper chest and arms. Keratosis develops later on the palms and soles with fissures, cracks and warty lesions.
Forty-one patients with chronic arsenic poisoning were randomly selected and treated with either spirulina extract plus zinc or placebo for 16 weeks. All were given a locally made water filter for their household water. The effectiveness of treatment was evaluated by comparing changes in the skin, as well as the arsenic content in urine and hair.
After two weeks on filtered water, there was a decrease in urinary excretion in the placebo group. In the spirulina group, there was a sharp increase in urinary excretion of arsenic. There was also a 47% drop in the amount of arsenic in hair sample in the spirulina group. There were also significant differences in the clinical appearance of melanosis and keratosis in spirulina treated participants.
One study with human subjects showed that spirulina may help eliminate arsenic from the body. Laboratory studies show protective effects of spirulina against arsenic, cadmium, carbon tetrachloride, fluoride, iron, lead and mercury.
Is Spirulina Safe?
In 2013, spirulina extract was approved by the U.S. Food and Drug Administration (FDA) as blue and green food colorings for candy and chewing gum. The primary concern about spirulina is potential contamination with other blue-gene algae that produce liver toxins and cancer-causing chemicals. In addition to specification limits for lead, arsenic, and mercury, the FDA requires hat spirulina extract used as a color test negative for microcystin toxin, which is produced by some species of cyanobacteria that could be potentially present in the water where Spirulina is grown and harvested.
According to Medline Plus : Blue-green algae products that are free of contaminants are POSSIBLY SAFE for most people when used short-term. Doses up to 19 grams per day have been used safely for up to 2 months. Lower doses of 10 grams per day have been used safely for up to 6 months. Side effects are typically mild and may include nausea, vomiting, diarrhea, abdominal discomfort, fatigue, headache, and dizziness.
But blue-green algae products that are contaminated are POSSIBLY UNSAFE, especially for children. Children are more sensitive to contaminated blue-green algae products than adults.
Contaminated blue-green algae can cause liver damage, stomach pain, nausea, vomiting, weakness, thirst, rapid heartbeat, shock, and death. Don't use any blue-green algae product that hasn't been tested and found free of microcystins and other contamination.
Special precautions & warnings:
Pregnancy and breast-feeding: Not enough is known about the use of blue-green algae during pregnancy and breast-feeding. Stay on the safe side and avoid use.
"Auto-immune diseases" such as multiple sclerosis (MS), lupus (systemic lupus erythematosus, SLE), rheumatoid arthritis (RA), pemphigus vulgaris (a skin condition), and others: Blue-green algae might cause the immune system to become more active, and this could increase the symptoms of auto-immune diseases. If you have one of these conditions, it's best to avoid using blue-green algae.
Bleeding disorders: Blue-green algae might slow blood clotting  and increase the risk of bruising and bleeding in people with bleeding disorders.
Phenylketonuria: The spirulina species of blue-green algae contains the chemical phenylalanine. This might make phenylketonuria worse. Avoid Spirulina species blue-green algae products if you have phenylketonuria.
Spirulina is an edible microorganism that has been consumed by humans since, at least, the 16th Century. It is a good source of protein and antioxidants. Its chemical properties make it attractive to researchers studying a variety of conditions, and pre-clinical studies have shown some promising results. However, there is not enough evidence in patients in double-blind, placebo-controlled studies to say that any of these results will be directly applicable to humans.
Given its favorable safety profile (with the possible exceptions stated above), I don’t see any reason that it couldn’t be part of a healthy diet.