Guide
How to choose a good bladderwrack
A checklist for reading any bladderwrack label: species, whole plant or extract, iodine per serving, a metals certificate, the amount, other ingredients and price per serving.
A good bladderwrack label tells you what most don't: the species, whether it's whole plant or extract, how much iodine is in a serving, and whether the lot has been tested for metals. Here are seven checks you can run on any bladderwrack powder, capsule or tablet.
1. Is the species named?
Look for Fucus vesiculosus. The NIH's LactMed monograph lists Fucus vesiculosus, other Fucus species and Ascophyllum nodosum together under "bladderwrack", and many labels say "kelp" or "seaweed" loosely. It matters: iodine differs by hundreds of times between seaweeds, from 16 mcg per gram in nori to over 8,165 mcg per gram in processed Laminaria kelp granules in one survey. A label that says only "sea vegetables" or "kelp blend" hasn't told you what you're buying. For background, see what is bladderwrack.
2. Whole plant or extract?
Whole powder is the dried plant. An extract is concentrated, so the milligrams aren't comparable. The one whole-plant trial found used 5 g a day of dried Fucus vesiculosus; the others used extracts at 300 to 2,000 mg a day. A label should say which it is and, for an extract, the ratio or what it is standardised to.
3. Is iodine stated per serving?
This is the number that matters most, and the one most often missing. In a Norwegian analysis of 96 seaweed products, iodine in supplements ranged from 5 to 5,600 mcg per daily dose, and species and iodine labelling was inadequate or inaccurate for several. Look for an iodine figure in mcg per serving, ideally from a lot-specific lab result. If none is given, treat the iodine as unknown, which for anyone with a thyroid condition is reason enough to ask first; see who should not take bladderwrack.
4. Is there a lab certificate for metals?
Seaweeds take up arsenic, cadmium and lead from the water. In an Italian analysis of 14 seaweeds, arsenic reached 67.6, cadmium 7.2 and lead 6.7 mg/kg dried weight, varying by two to four orders of magnitude between species. A 2007 case report traced one woman's two-year illness to a kelp supplement with 8.5 mg/kg arsenic, and eight of nine kelp products tested in the same report exceeded the FDA's tolerance for certain foods. "Organic" or "wild-harvested" describes how a plant was grown or gathered, not the metals in it. Look for a current certificate of analysis that reports arsenic, cadmium and lead, linked from the product page. A brand that won't share one when asked is telling you something.
5. Is the amount stated, and how does it compare with trials?
A milligram amount per serving, with the plant part or extract named, lets you compare. No dose has been shown to be effective, so a bigger number is not a better product; and the trials' amounts, up to 5 g a day, are not a target. See how much bladderwrack to take a day.
6. What else is in it?
Capsules need a shell, and many need a flow agent; that is normal. What to check is whether the other ingredients are listed in full, and whether the bladderwrack sits inside a proprietary blend that hides its amount.
7. Price per serving
Divide the price by the number of servings, then compare at a similar amount and form. Because no dose is shown to work better, a cheaper serving of a labelled, tested product is a fair comparison; a cheap one with no iodine figure and no certificate is not.
Questions people ask
Which bladderwrack supplement or form should I choose?
No research ranks brands or forms. Powder, capsules and tablets are all dried plant; extracts are a different product. The checks above are the closest thing to an objective comparison.
Where can I buy bladderwrack powder or seaweed?
It is sold as dried seaweed, powder, capsules, tablets and tea by herb suppliers, supplement sellers and some grocers. Wherever you buy, run the checks above; "bladderwrack and fennel hand wash" is a soap, not a supplement, and none of this applies to it.
Do bladderwrack reviews help?
Reviews can tell you about taste, capsule size and shipping. They can't tell you the iodine or metal content of the lot you received, and a reviewer can't see a thyroid change building over weeks.
Where do I get bladderwrack in Dave the Diver?
That is a video game, and its in-game ingredient is outside this guide. For the real seaweed, see above.
Sources
- Seaweed A National Institutes of Health reference monograph describes bladderwrack as the dried whole plant, notes it contains iodine and can contain arsenic, cadmium and lead, and says labelled and actual contents often differ across supplements.
- 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.
- Essential and toxic elements in seaweeds for human consumption In 14 edible seaweeds, arsenic reached 67.6, cadmium 7.2 and lead 6.7 mg/kg dried weight, varying widely by species.
- Case report: potential arsenic toxicosis secondary to herbal kelp supplement One woman's two-year illness was traced to arsenic in a kelp supplement and resolved after she stopped it; 8 of 9 kelp products tested exceeded the FDA food tolerance level.
- 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.
- 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.
*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.