Benefits
Total and LDL cholesterol levels
A meta-analysis of 7 randomized trials found spirulina lowered total cholesterol, LDL and triglycerides and raised HDL; the effect grew with longer use but did not depend on dose. In a controlled crossover in healthy adults with normal cholesterol, 4.8 g a day for 17 days did not change any blood lipid compared with placebo.
Healthy blood pressure levels in adults
A meta-analysis of randomized trials in adults, rated moderate certainty, found spirulina lowered systolic blood pressure by about 4.4 mmHg and diastolic by about 2.8 mmHg, with high variation between trials. Effects held in people with high blood pressure, overweight adults, adults over 50 and use longer than 8 weeks; blood pressure did not change in the short crossover in healthy adults.
C-reactive protein and other inflammation markers
Pooled trials found spirulina lowered C-reactive protein by about 0.55 mg/L, with high variation between trials and no clear link to dose or duration. Another pooled analysis found no significant change in the oxidative stress marker MDA or in TNF-alpha, and only a borderline drop in IL-6.
Nasal comfort in a placebo-controlled study
In a double-blind, placebo-controlled trial in people with allergic rhinitis, spirulina improved nasal discharge, sneezing, nasal congestion and itching compared with placebo. This single trial has not been repeated. France's food safety agency advises people with an allergic predisposition not to take spirulina supplements.
Fasting blood sugar levels
A pooled analysis of 8 studies in adults with type 2 diabetes found spirulina lowered fasting glucose by about 18 mg/dL but did not significantly change HbA1c or post-meal glucose. A 3-month placebo-controlled trial of 2 g a day added to metformin reported lower HbA1c and fasting glucose, while glucose did not change in healthy adults.
Mechanism of action
Protein, vitamins and pigments
Spirulina is grown mainly for its protein and also supplies vitamins A, C and E, iron, magnesium, zinc and other minerals, gamma-linolenic acid and phycobiliprotein pigments such as C-phycocyanin. Which of these, if any, explains the lipid and blood pressure findings in trials has not been shown.
Cholesterol absorption and synthesis
Spirulina has been proposed to lower cholesterol by reducing its absorption from the gut. In a placebo-controlled crossover in adults with normal cholesterol, 4.8 g a day for 17 days did not change blood markers of cholesterol absorption (campesterol, sitosterol, cholestanol) or synthesis (lathosterol).
Inflammation and oxidative stress markers
In pooled human trials, spirulina lowered C-reactive protein, while MDA and TNF-alpha did not change and IL-6 and TBARS fell only marginally (significantly only in people with a BMI under 25). A rise in IL-2 did not hold up in sensitivity analysis.
Clinical trials
Systematic review and random-effects meta-analysis of 7 randomized controlled trials, literature searched to July 2015. The abstract does not report the total number of participants (Serban et al. 2016, Clin Nutr)
Adults in 7 randomized controlled trials.
Spirulina lowered total cholesterol by about 46.8 mg/dL, LDL by about 41.3 mg/dL and triglycerides by about 44.2 mg/dL, and raised HDL by about 6.1 mg/dL. The changes grew with longer use but did not depend on dose.
Systematic review and meta-analysis of randomized clinical trials in adults, searched to April 2024 and registered in PROSPERO (CRD42024534608); certainty of evidence rated moderate, too few studies for dose-response conclusions (Shiri et al. 2025, Phytother Res)
Adults in randomized clinical trials, with subgroups of people with hypertension, overweight adults and adults over 50.
Systolic blood pressure fell by about 4.41 mmHg and diastolic by about 2.84 mmHg, with substantial heterogeneity between trials (I2 66.1% and 62.3%). Blood pressure was still lower in people with hypertension, overweight adults, adults over 50 and trials longer than 8 weeks.
Randomized, double-blind, placebo-controlled crossover with spirulina, wakame and placebo periods of 17 days separated by washouts of at least 14 days; spirulina capsules supplied by Flora Health, placebo microcrystalline cellulose; authors declared no conflicts of interest (van den Driessche et al. 2020, Eur J Nutr)
36 healthy adults without high cholesterol randomized, 35 analyzed (15 men, 20 women).
Compared with placebo, 4.8 g/day of spirulina did not change total cholesterol (P = 0.443), LDL cholesterol (P = 0.677), HDL or triglycerides, markers of cholesterol absorption and synthesis, plasma glucose, or systolic and diastolic blood pressure.
Systematic review and random-effects meta-analysis of 8 studies (9 arms), searched to August 2020 (Hatami et al. 2021, J Diabetes Metab Disord)
Adults with type 2 diabetes in 8 studies.
Spirulina lowered fasting blood glucose by about 17.9 mg/dL, triglycerides by about 31.0 mg/dL, total cholesterol by about 18.5 mg/dL and LDL by about 20.0 mg/dL. HbA1c and post-meal blood sugar did not change significantly.
Small randomized trial against a control group; an early single trial whose HbA1c result was not confirmed in a later pooled analysis (Parikh et al. 2001, J Med Food)
25 people with type 2 diabetes. 2-month intervention.
Fasting and post-meal glucose fell and HbA1c fell significantly. Triglycerides fell significantly, total and LDL cholesterol fell, HDL rose marginally, apolipoprotein B fell and apolipoprotein A1 rose.
Randomized, double-blind, placebo-controlled add-on trial; both groups stayed on metformin. The abstract does not give the number who completed or state clearly which changes are compared with placebo (Karizi et al. 2023, Phytother Res)
60 adults with type 2 diabetes not adequately controlled on metformin.
The abstract reports HbA1c down by 1.43 and fasting blood sugar down by 24.94 mg/dL with spirulina, triglycerides lower than with placebo, total cholesterol down by 41.36 mg/dL, LDL down by 38.4 mg/dL and HDL up by 3 mg/dL. No adverse events were reported.
Double-blind, placebo-controlled trial; the abstract does not report sample size, dose or duration (Cingi et al. 2008, Eur Arch Otorhinolaryngol)
People with allergic rhinitis.
Spirulina improved nasal discharge, sneezing, nasal congestion and itching, and physical findings, compared with placebo (P < 0.001).