Spirulina: Nutrients per Serving, the B12 Problem, Evidence and Safety

Spirulina is the dried biomass of Arthrospira platensis, a blue-green alga grown in alkaline water and sold as a dark green powder, tablet or capsule. By weight it is rich: about 57 g of protein and 28.5 mg of iron per 100 g. By serving it is modest, because FSSAI's schedule permits 500 to 3,000 mg a day, and 3 g carries about 1.7 g of protein and 0.9 mg of iron. Its vitamin B12 is mostly an inactive look-alike. This entry sits in the supplements section of the handbook.

Two subjects are handled in full elsewhere and only summarised here. The vitamin itself, with requirements and reliable sources, is in the handbook entry on vitamin B12, and the mineral in the handbook entry on iron. What follows is specific to spirulina: the arithmetic of a serving, the trials, contamination and the Indian rules.

What is spirulina?

Spirulina is a cyanobacterium, a photosynthetic microorganism commonly called blue-green algae, that is harvested, dried and milled. The trade name comes from an older classification; the organisms sold are now recognised as two Arthrospira species, platensis and maxima. FSSAI's schedule lists it as spirulina (algae) from Spirulina platensis (Arthrospira platensis), with the Hindi name shaiwal. The blue pigment phycocyanin, extracted from the same organism, has a separate entry in the schedule with its own limit of 50 to 250 mg a day.

How much nutrition is in a serving of spirulina?

Much less than the per 100 g figures on a jar suggest. The United States Department of Agriculture's food composition database lists dried spirulina at 290 kcal, 57.47 g of protein, 28.5 mg of iron and 120 mg of calcium per 100 g, and gives a tablespoon as 7 g. FSSAI's upper limit of 3,000 mg is less than half a tablespoon. Scaled to 3 g, the protein falls to about 1.7 g and the iron to about 0.9 mg. The Indian Food Composition Tables (2017) carry no entry for spirulina, which is why the figures here are American.

The allowances in the last column are ICMR-NIN's 2020 recommended dietary allowances for adults, with protein worked at 0.83 g per kg for a 65 kg man and a 55 kg woman. The percentages are this entry's own arithmetic, and they say nothing about how well the iron is absorbed, which the sources read here did not measure.

Spirulina against dal and greens on an Indian plate

Ordinary Indian foods outdo a 3 g serving on every nutrient the jar advertises. Thirty grams of raw masoor dal, roughly one katori once cooked, supplies about 7.3 g of protein and 2.1 mg of iron on IFCT 2017 values. A 100 g portion of amaranth leaves supplies 4.6 mg of iron and 8,553 mcg of beta-carotene, against about 10 mcg in the spirulina. The pages for masoor dal and amaranth leaves give the full tables, and the iron ranking lists other foods.

The Indian position: no ICMR-NIN requirement, an FSSAI range of 500 to 3,000 mg

ICMR-NIN sets no requirement for spirulina, which is to be expected for a food. Its Dietary Guidelines for Indians (2024) mention dried spirulina once, in a table of the approximate quantity of each food needed to furnish 100 mg of omega-3 fat: 12 g, four times FSSAI's daily maximum. On that table 3 g would give about 25 mg. The handbook entry on omega-3 fatty acids covers the sources that matter more.

FSSAI's health supplement and nutraceutical regulations list spirulina in Schedule VI, Part A, with a permitted range of 500 to 3,000 mg a day and purity criteria: protein at least 55 per cent, carbohydrate at most 30 per cent, fat not more than 10 per cent, ash 5 to 10 per cent and moisture 3 to 6 per cent, with the fatty acid profile to be mentioned on the package. The range is what a product may direct you to take. The schedule read here is the compendium of 29 September 2021; later amendments were not checked.

Does spirulina supply vitamin B12?

Not in a form you can rely on. A 1999 analysis of spirulina tablets found that a bacterial growth assay read six to nine times more B12 than an assay based on intrinsic factor, the protein the human gut uses to absorb the vitamin. When the compounds were purified, 83 per cent was pseudovitamin B12, an analogue, and 17 per cent was true B12. The USDA database lists vitamin B12 in dried spirulina as zero. ICMR-NIN's 2020 allowance for adults is 2.2 mcg a day.

A study in B12-deficient children fed algae, including spirulina, makes the practical point. Their plasma B12 readings rose, but the size of their red blood cells, already abnormal, got worse, while children given fish or a B12 supplement improved. The authors concluded that it was unjustified to advocate algae as a safe source. The lesson for a vegetarian is twofold: spirulina does not replace a fortified food or a supplement, and a blood report may look better than the body is. Vitamin B12 for vegetarians sets out the options.

What does the trial evidence say about spirulina?

There are positive findings from small trials, and they deserve a cautious reading. A 2016 meta-analysis of seven randomised trials reported lower total cholesterol (by 46.8 mg/dL), LDL cholesterol (41.3 mg/dL) and triglycerides (44.2 mg/dL) and higher HDL cholesterol (6.1 mg/dL). A 2021 meta-analysis of eight studies in people with type 2 diabetes found smaller falls in cholesterol and a fall in fasting glucose of 17.9 mg/dL, with no significant effect on HbA1c or post-meal glucose. One of the early trials was Indian: 25 people with type 2 diabetes in Vadodara, given 2 g a day for two months.

For blood pressure, a 2021 meta-analysis pooled five trials with 230 participants who took 1 to 8 g a day for 2 to 12 weeks. Systolic pressure fell by 4.6 mmHg and diastolic by 7.0 mmHg, mostly in people who already had hypertension, and the authors asked for more exact trials. For weight, five studies pooled in 2019 showed a loss of 1.56 kg, with no significant change in body mass index.

The evidence is weak to moderate at best. Each pooled result rests on five to eight short trials, the diabetes analysis reported wide disagreement between studies on cholesterol, and the blood pressure trials used up to 8 g a day, well above the FSSAI range. None of the papers read for this entry measured heart attacks, strokes or diabetes complications. These are changes in laboratory readings over weeks, and they are no basis for replacing a prescribed medicine or the dietary approach to cholesterol.

Where do the contamination risks come from?

The risk comes from what grows or settles alongside the spirulina, not from the organism itself, which does not normally produce toxins. A 2017 Canadian study tested 18 algae supplements, 14 of them spirulina, for cyanotoxins, the toxins made by some other blue-green algae. Eight contained some, and four exceeded tolerable daily intake values. Three of the 14 spirulina products carried microcystins at 0.25 to 0.84 micrograms per gram. The WHO tolerable intake quoted in the paper is 0.04 micrograms per kg of body weight, or 2.4 micrograms a day for a 60 kg adult.

Other surveys were more reassuring about spirulina and less so about its relatives. A German study of 13 algae products found microcystins only in those made from Aphanizomenon flos-aquae, a different blue-green alga, although extracts of every product were toxic to cells in the laboratory. An analysis of 25 spirulina products sold worldwide found mercury at 0.002 to 0.028 mg per kg, within the limits the author applied; it did not measure lead, arsenic or cadmium. No Indian market survey was found, so nothing can be said here about products sold in India.

A worked example: spirulina tablets for a vegetarian in Chennai

This case is an illustration, not a real person. A 24-year-old lacto-vegetarian woman in Chennai who weighs 55 kg has been told that spirulina will fix her tiredness. The bottle holds 120 tablets of 500 mg and directs two tablets twice a day.

How do you check a spirulina label before buying?

Look for the declarations FSSAI's regulations require of a nutraceutical, and then for the facts that bear on contamination. The pack must carry the word NUTRACEUTICAL, the common name, the amount of the ingredient, a recommended usage advisory, the warning NOT FOR MEDICINAL USE and a statement about storing it away from children. It may not claim to prevent, treat or cure a disease. The schedule adds one item particular to spirulina, the fatty acid profile.

Common mistakes and myths about spirulina

The commonest mistake is reading a per 100 g panel as if it described a serving. The second is counting spirulina towards B12 and dropping a fortified food or supplement. The third is treating the trial results as a reason to adjust a diabetes, cholesterol or blood pressure medicine. The fourth is assuming that natural means clean, which the contamination studies do not bear out. To see what your protein target is before judging any product, use the protein calculator.

Side effects, safety and who should ask a doctor first

For healthy adults the record is fairly good. A United States Pharmacopeia expert committee reviewed human trials, animal studies and 31 adverse event reports and gave Spirulina platensis and Spirulina maxima its Class A safety rating, while noting that it may revisit the rating. In a survey of 150 Polish users of microalgae supplements, the side effects reported most often were diarrhoea, nausea, abdominal pain and skin rash. People with kidney failure or an underactive thyroid reported more of them, and those who had consulted a professional reported fewer.

Ask a doctor before taking spirulina if you are pregnant or breastfeeding, have kidney or thyroid disease, or take medicines for diabetes, blood pressure or cholesterol, since the trials suggest it can shift those readings. Anyone on a phenylalanine-restricted diet should know that dried spirulina contains about 2.8 g of phenylalanine per 100 g. Children are a particular concern: the toxin study notes that the tolerable intake for a 30 kg child is half the adult figure. Stop and seek medical advice for a rash or persistent stomach upset.

NNWA courses that cover supplements such as spirulina

Reading a claim like those on a spirulina jar is a skill taught in NNWA's Dietary Supplements and Nutraceuticals course, and food-first protein and iron planning in the Diploma in Nutrition. NNWA is a Kolkata skill academy in the private sector, with classes held online in English and in Hindi. Learners are trained to coach healthy people and to pass medical cases on to a doctor; no NNWA course is a degree or a dietitian qualification.