Limited evidenceImmunity

Fucoidan

A sulphated polysaccharide from brown seaweed. Several small randomized trials show it shifts immune markers, but none has shown that it reduces infections or illness.

Evidence last reviewed: August 2026

What the science says

Better antibody response to influenza vaccine in older adults Limited evidence
A randomized trial in elderly Japanese men and women found that fucoidan supplementation increased antibody titres after seasonal influenza vaccination. The trial was small and measured antibody levels, not whether anyone actually got influenza.
Immune and inflammatory markers shift in patients Limited evidence
A randomized, double-blind, placebo-controlled trial of oligo-fucoidan in asthma reported changes in immune and inflammatory measures and in some pulmonary function parameters. Marker-level results in one small trial do not establish a clinical benefit.
No trials of infection rates Limited evidence
Across the fucoidan literature the outcomes are laboratory measures — cytokines, natural killer cell activity, antibody titres. No trial has used incidence or duration of infection as its endpoint.

Dosage & safety

Studied doseTrials have used roughly 300 mg per day of purified fucoidan; commercial products range from 300 to 1000 mg per day. There is no established optimal dose.

SafetyGenerally well tolerated with mild gastrointestinal effects. Brown seaweed products can carry substantial iodine, which matters for anyone with thyroid disease, and heavy metal content depends on sourcing. Fucoidan has heparin-like anticoagulant activity in vitro, so caution is warranted with blood thinners and before surgery. Not studied in pregnancy.

Scientific references

Supplementation of elderly Japanese men and women with fucoidan from seaweed increases immune responses to seasonal influenza vaccination
Negishi H, Mori M, Mori H, Yamori Y — J Nutr, 2013
Effects of oligo-fucoidan on the immune response, inflammatory status and pulmonary function in patients with asthma: a randomized, double-blind, placebo-controlled trial
Yeh CW, Shih CJ, Liu TC, Chiou YL — Sci Rep, 2022

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