Ascophyllum nodosum is a brown seaweed, often called kelp. This seaweed provides iodine and trace minerals. People take it to support thyroid function because iodine is essential for producing thyroid hormones. Some also use it as a general mineral supplement.
You can find it as a powdered seaweed or in capsules. The iodine content shifts from batch to batch, so dosing is not fixed. Follow the label on the product you choose.
This kelp can hold very high levels of iodine. Combining it with other iodine supplements risks excessive intake. If you have hyperthyroidism or take thyroid medication like levothyroxine, speak with a healthcare provider before using it. The tolerable upper intake level for iodine in adults is roughly 1,100 micrograms per day.