1–8 g/day.
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Spirulina is a blue-green cyanobacterium (not strictly an alga, although it is commercially called one) that grows in warm alkaline lakes in the tropics, where it forms colonies visible from the air; it has been consumed for centuries by peoples around Lake Texcoco in Mexico and Lake Chad in Africa, and NASA included it in the 1970s as an ideal food for space missions because of its exceptional nutritional density: up to 70 percent of its dry weight is complete protein with all the essential amino acids.
Beyond its value as a concentrated food, clinical research over the past two decades has documented modest but significant effects on lipid profile, blood pressure, inflammation markers, and immune response at supplemental doses of 1-8 grams daily, which makes it one of the few food-supplements with clinical evidence that goes beyond "superfood" marketing.
The strongest evidence for supplemental spirulina concerns the lipid profile: several meta-analyses have shown modest but significant reductions in total cholesterol (10-20 mg/dL), LDL (10-25 mg/dL), and triglycerides (15-40 mg/dL), along with increases in HDL (2-5 mg/dL), at doses of 1-8 grams daily for 8-16 weeks in people with mild to moderate dyslipidemia.
For blood pressure, several trials have shown reductions of 4-7 mmHg in systolic and 3-5 mmHg in diastolic pressure with long-term use at doses of 2-4 g/day in people with mild hypertension; the mechanism combines antioxidant effects that improve endothelial function with a possible effect on the renin-angiotensin system mediated by bioactive peptides from the cyanobacterium itself.
One indication with interesting clinical data is seasonal allergic rhinitis: several trials have shown significant reductions in symptom scores (congestion, sneezing, itching, tearing) with 2 grams daily of spirulina for 6-12 weeks, with an effect comparable to that of second-generation antihistamines but without drowsiness or anticholinergic effects.
The immunomodulatory effect appears to be related to modulation of the Th2 response (responsible for allergic reactions) toward a more Th1 balance, in addition to reducing histamine release and modulating the proinflammatory cytokines associated with allergic reactions; this profile makes it a reasonable option for people with mild allergy who prefer to avoid continuous antihistamine medication.
Spirulina contains phycocyanin, a unique blue pigment with antioxidant and anti-inflammatory activity documented in mechanistic studies; several trials have shown improvements in oxidative stress markers (MDA, glutathione, total antioxidant capacity) with long-term use at doses of 4-6 g/day, especially in people with chronic low-grade inflammation associated with obesity, diabetes, or aging.
The doses studied range from 1 to 8 grams daily depending on the indication: 1-2 g/day as a general nutritional supplement, 2-4 g/day for allergic rhinitis, 4-8 g/day for lipid profile and cardiometabolism; ideally divided into two or three doses with meals, as a powder (mixed into smoothies, juices, or yogurt) or in capsules; clinical effects appear between 4 and 12 weeks.
The most important precaution is product quality: spirulina grown in contaminated waters can contain heavy metals (lead, mercury, cadmium) and microcystins (toxins produced by other cyanobacteria that can contaminate cultures), so it is advisable to choose products with quality certification and purity testing; people with phenylketonuria should avoid it because of its phenylalanine content, those with active autoimmune diseases should use caution because of its immunostimulant effect, and caution is advised in pregnancy and breastfeeding because of limited data.
Information, not medical advice. Scientific evidence reflects the quality of the studies.