kelp
Meaning of kelp: Large brown seaweed sold as a supplement, notable in medicine mainly for how much iodine it carries.
Definition of kelp
Kelp is a group of large brown seaweeds that grow in cold coastal water, including species of Laminaria. It is eaten in several cuisines and sold as a dried supplement in tablet and powder form. Its main significance in medicine is its iodine content, which is high and variable, and the alginate extracted from it, which is used in dressings and in food manufacture.
Why does the iodine content matter?
The thyroid gland uses iodine to make its hormones, and it needs a modest and steady supply. Kelp concentrates iodine from seawater to levels far above those in ordinary food, and the amount in any given product varies with the species, where it grew and how it was processed. Both extremes cause trouble: too little iodine leads to an underactive gland and goiter, while a sudden large load can push a gland either way, provoking overactivity in some people and shutting down hormone production in others. Cases of thyroid disturbance traced to kelp supplements are documented in the medical literature.
What is it used for?
| Use | Basis |
|---|---|
| Food | A traditional ingredient in several coastal cuisines |
| Alginate extraction | Wound dressings, dental impressions, food thickeners |
| Cervical dilators | Dried stems swell with moisture and widen the cervix |
| Dietary supplement | Sold for thyroid support, energy and weight loss |
What do the health claims amount to?
Marketing attaches a long list of benefits to kelp, among them immune stimulation, weight loss and anticancer effects. These rest largely on laboratory work with isolated compounds rather than on studies in people, and none is established. The seaweed does contain a mixture of fiber, minerals, and compounds including plant sterols, which is the usual starting point for such claims. Evidence that swallowing the whole dried plant produces any of the promised effects is lacking.
Are there risks?
Two are recognized apart from the thyroid. Seaweed absorbs heavy metals from the water it grows in, and arsenic has been found in commercial kelp products at levels prompting regulatory warnings. And because supplements are not held to the testing standards applied to medicines, the iodine content stated on a label may differ substantially from what a tablet contains. Iodine also interacts with thyroid medication and with certain other drugs.
Also known as
Used in a sentence
The patient's abnormal thyroid results were attributed to a kelp supplement taken daily.
Good to know
The iodine content of kelp supplements is high and inconsistent between products, and both overactive and underactive thyroid states have been traced to their use.