Spirulina and blood pressure.

The primary study: Ku et al. (2013)

The most important clinical evidence for spirulina and blood pressure: a randomised controlled trial by Ku et al., published in Nutrition Research, involving 40 adults with stage 1 hypertension (systolic 130–159 mmHg). Participants were randomised to 4.5 g/day of spirulina or placebo for 3 months.

Results:

• Systolic blood pressure reduced by approximately 8 mmHg in the spirulina group (from ~148 to ~140 mmHg).
• Diastolic blood pressure reduced by approximately 6 mmHg.
• Lipid peroxidation markers (TBARS) were also significantly reduced.
• No adverse effects reported.

An 8 mmHg systolic reduction is clinically meaningful — equivalent to the effect of modest aerobic exercise or early dietary sodium restriction. For context, the DASH diet (one of the most evidence-based dietary interventions for hypertension) produces approximately 8–14 mmHg systolic reduction.

Proposed mechanisms

Several mechanisms have been proposed for the antihypertensive effect:

1. Endothelial oxidative stress reduction.Oxidative stress in the vascular endothelium reduces nitric oxide (NO) bioavailability. NO is the primary endogenous vasodilator — its reduction drives vasoconstriction and elevated blood pressure. Phycocyanin’s antioxidant activity preserves NO by reducing the superoxide that would otherwise quench it.
2. Anti-inflammatory effects on vascular tone. COX-2 inhibition reduces prostaglandins that promote vasoconstriction. Reduced vascular inflammation is associated with improved arterial compliance and lower blood pressure.
3. Lipid-lowering contribution. Reduced LDL oxidation and lower triglycerides improve endothelial function. The lipid and blood pressure effects may be mechanistically linked through a shared endothelial pathway.

The evidence gap

A single RCT (n=40, 3 months) is not sufficient to make strong evidence-based recommendations. The effect needs to be replicated in larger trials across diverse populations before spirulina can be recommended as a blood pressure intervention alongside established first-line approaches (sodium restriction, exercise, DASH diet, antihypertensive medication when indicated).

Who this is most relevant for

The blood pressure evidence is most relevant for:

• Adults with stage 1 hypertension managed with lifestyle— where adding spirulina to dietary modification is low-risk and plausibly beneficial based on the Ku et al. data.
• People already taking spirulina for other reasons — the potential antihypertensive effect is a real and evidence-based secondary benefit.

Spirulina is not a substitute for antihypertensive medication when that is clinically indicated. Stage 2 hypertension (systolic ≥160 mmHg) requires medical management; dietary interventions alone are insufficient.

Interactions with blood pressure medications

If you are taking antihypertensive medication, the additional blood pressure reduction from spirulina at 4.5 g/day could be additive. This is unlikely to cause problems at this effect size, but worth monitoring. Inform your prescriber if you are starting spirulina alongside antihypertensive treatment.

Dose

The Ku et al. study used 4.5 g/day. This is consistent with the doses used in the cholesterol and liver health literature. 1–2 g/day (common in general supplementation) may produce a smaller or undetectable effect; the blood pressure data is specifically at 4.5 g.