Guide
How much bladderwrack should you take a day?
There is no established daily dose of bladderwrack. Trials used from 300 mg of extract to 5 g of dried plant, and the limiting factor is iodine, which varies widely between products.
There is no established daily dose of bladderwrack. No dietary reference intake exists for it, and the trials used anything from 300 mg of extract to 5 g of dried plant a day. What limits a sensible amount is not the milligrams but the iodine, which varies from product to product and is rarely stated on the label.
What the trials used
These are study amounts, not recommendations. Most were in people selected for a medical condition, and most used extracts.
| Preparation | Daily amount | Length | Who |
|---|---|---|---|
| Dried Fucus vesiculosus (whole plant) | 5 g | 5 weeks | 36 adults with type 2 diabetes (three arms) |
| Bladderwrack seaweed (case series) | 700 mg, then 1.4 g | not extracted | 3 pre-menopausal women, no control group |
| Fucus extract, 85% fucoidan | 300 mg | 12 weeks | 122 adults with osteoarthritis |
| Two-species brown seaweed extract | 500 mg | 12 weeks | 56 overweight adults with prediabetes |
| Polyphenol-rich Fucus extract | 2,000 mg | 12 weeks | 34 overweight adults with high LDL |
The only whole-plant trial used 5 g a day, many times a capsule-sized amount, and found no change in blood glucose. None of these trials set out to find a best dose, so none identifies one. The results are reviewed in bladderwrack benefits: what the research does and doesn't show.
Why iodine sets the ceiling
The American Thyroid Association's statement on iodine gives the US adult recommended intake as 150 mcg a day and the tolerable upper limit as 1,100 mcg a day, and advises against iodine or kelp supplements that deliver more than 500 mcg a day. Seaweed iodine is hard to predict. In a Norwegian analysis of 96 seaweed products, supplements ranged from 5 to 5,600 mcg of iodine per daily dose, and species and iodine labelling was inadequate or inaccurate for several. A separate survey found iodine from 514 to 6,571 mcg per gram in two Namibian kelps, depending on blade age and bleaching.
The arithmetic is simple, even if the inputs are unknown: iodine per dose is grams of seaweed times micrograms of iodine per gram. A seaweed at 100 mcg per gram would give 100 mcg in a gram and 500 mcg in 5 g; at 1,000 mcg per gram, a single gram reaches the upper limit. Those are illustrative figures, not measurements of any product. Without an iodine value for the lot you hold, the milligram amount cannot tell you where you land.
In a four-week trial in 36 healthy adults, kelp capsules (two or four a day) raised TSH at both doses, and in 42 women, 0.5 g a day of a brown seaweed for two weeks raised TSH, with two women above the normal range. Those were not bladderwrack, but they are why this page won't name an amount as "safe".
Powder, capsule or extract: the milligrams mean different things
An extract is concentrated, so 500 mg of extract is not comparable with 500 mg of whole powder. A label that says "bladderwrack 500 mg" without saying whole plant or extract, and without a ratio for an extract, hasn't told you what you are getting.
Questions people ask
How much bladderwrack should I take daily?
No amount can be recommended, because none has been established. If you take a product, don't exceed its label, and if you have a thyroid condition or take thyroid medication, ask a clinician first.
How much bladderwrack powder is a safe amount?
Powder is the whole dried plant, so its iodine depends on the lot. Without an iodine figure from the supplier, no powder amount can be called safe. A level teaspoon is also not a reliable measure of weight.
How much bladderwrack should I mix with sea moss?
No research tests blends. If you combine seaweeds, the iodine from each adds up, so check the stated iodine for each product and count iodine from any multivitamin or iodised salt too.
How long can I take it?
The trials ran for 2 to 12 weeks. We found no long-term safety data for whole bladderwrack. For timing, see when is the best time to take bladderwrack; for who should check first, who should not take bladderwrack.
Sources
- The Effect of Sargassum fusiforme and Fucus vesiculosus on Continuous Glucose Levels in Overweight Patients with Type 2 Diabetes Mellitus: A Feasibility Randomized, Double-Blind, Placebo-Controlled Trial In 36 adults with type 2 diabetes, 5 g a day of dried bladderwrack for 5 weeks did not change average blood glucose.
- Twelve weeks' treatment with a polyphenol-rich seaweed extract increased HDL cholesterol with no change in other biomarkers of chronic disease risk in overweight adults: A placebo-controlled randomized trial In 34 overweight adults with high LDL, 2,000 mg a day of a bladderwrack extract for 12 weeks raised HDL slightly; nothing else changed.
- Marginal Impact of Brown Seaweed Ascophyllum nodosum and Fucus vesiculosus Extract on Metabolic and Inflammatory Response in Overweight and Obese Prediabetic Subjects In 56 overweight adults with prediabetes, 500 mg a day of a brown-seaweed extract for 12 weeks did not change blood glucose or body weight.
- Effects of fucoidan from Fucus vesiculosus in reducing symptoms of osteoarthritis: a randomized placebo-controlled trial In 122 adults with hip or knee osteoarthritis, 300 mg a day of a bladderwrack fucoidan extract for 12 weeks did no better than placebo and was well tolerated.
- The effect of Fucus vesiculosus, an edible brown seaweed, upon menstrual cycle length and hormonal status in three pre-menopausal women: a case report In 3 pre-menopausal women, 700 mg to 1.4 g a day of bladderwrack lengthened menstrual cycles; there was no control group.
- Commercially available kelp and seaweed products - valuable iodine source or risk of excess intake? A lab test of 96 seaweed products found iodine in supplements ranging from 5 to 5,600 mcg per daily dose, and labels were often inadequate or inaccurate.
- Variability of iodine content in common commercially available edible seaweeds Seaweed iodine ranged from 16 to over 8,000 mcg per gram across species and varied a lot within one species.
- Effects of kelp supplementation on thyroid function in euthyroid subjects In 36 healthy adults, 4 weeks of kelp capsules raised TSH in both the low-dose and high-dose groups, and most values returned to baseline after stopping.
- Low-level seaweed supplementation improves iodine status in iodine-insufficient women In 42 women, 0.5 g a day of a brown seaweed (Ascophyllum nodosum, not bladderwrack) for 2 weeks raised iodine excretion and TSH, with two women above the normal range.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.