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Underactive Thyroid not helped by Seaweed

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Many people start to take seaweed as part of their diet if they become concerned about developing an underactive thyroid. This is because an underactive thyroid can develop if you do not have enough iodine in your diet. Learn more here.


Underactive Thyroid not helped by Seaweed

by Monica Wilde
17 November 2014

If a thyroid test still shows high TSH levels, despite adequate iodine intake, there may be other factors influencing your thyroid function. In fact, it might even be due to the increase of iodine transport into the thyroid and not a problem. Read more about the issues.

Many people start to take seaweed as part of their diet if they become concerned about developing an underactive thyroid. This is because an underactive thyroid can develop if you do not have enough iodine in your diet.

Ensuring you have adequate iodine in your diet is essential to prevent one of the main causes of underactive thyroid (called subclinical hypothyroidism). Sufficient iodine can be got from eating any ONE of the following EVERY day.

  • Two large eggs
  • Three large glasses of non-organic milk*
  • One and half whole mackerel
  • Half a teaspoon of seaweed
  • One Napiers Seagreens Organic Hebridean Kelp Capsule

We know from both our work with patients and also our research with Glasgow University1 that taking one Napiers Seagreens Organic Hebridean Kelp Capsule a day provides sufficient iodine to stimulate greater production of TSH (thyroid stimulating hormone) in people with iodine insufficiency and low levels of TSH1.

In the first instance, without symptoms of any other conditions, it is sensible to ensure sufficient daily dietary iodine to see whether this corrects the underactivity. If it does then the thyroid imbalance has been corrected and you are now euthyroid (normal).

However, sadly in some cases taking seaweed to ensure sufficient iodine intake does not correct an underactive thyroid. This can be for a variety of reasons.

What influences thyroid test results?

TSH, free T4, and free T3 tests are just a "snapshot" of what is going on in your body on a given day and test results can vary, influenced by quite a few things. If you have an underactive thyroid gland that has not responded to seaweed intake, it may be due to a range of factors.

Severe stress can affect your thyroid test results. We often find that if someone has suffered stress over a prolonged period of time then they need more than seaweed to correct dietary imbalance but that they need support for their adrenal glands and endocrine system. This is usually done with adaptogenic herbs. If you have been very stressed it is worth consulting a herbalist for expert advice.

Being ill can affect your thyroid test results. If you have been in hospital, have had a long-term illness, have had liver disease or are recovering from a nasty illness it is best to delay your thyroid test until you have fully recovered when, typically, your thyroid hormone levels should return to normal. FT3 levels in particular can be lower than usual in a nonthyroidal illness (NTI).

Being pregnant (especially in the first three months) can affect your thyroid test results. The developing baby needs a lot of iodine as this is crucial to normal brain development. So ensure you have the best diet possible, including seaweed and other sources of iodine, vitamins and minerals, and ask to be retested later.

Some medicines may influence thyroid test results. Thjs includes aspirin, oestrogen and levothyroxine among other drugs. Make sure your doctor is aware of all medicines (including those you have bought yourself) before your thyroid test.

Thyroid dysfunction can affect your thyroid test results. Acute or chronic thyroid dysfunction may be diagnosed and very occasionally there is a problem in the pituitary gland producing unregulated levels of TSH. Your body may also have developed a resistance to thyroid hormones or there may be increases, decreases, and changes in the proteins that bind T4 and T3.

Iodine supplementation raises TSH levels.

TSH is the hormone responsible for facilitating sodium-iodine symporter. Pituitary-derived TSH has been known for decades to stimulate iodide transport into the thyroid gland via the adenylate cyclase cAMP pathway. So when you increase the amount of iodine in your diet, you may also increase the amount of TSH that enables the iodine to be imported into the thyroid gland. This is often a temporary increase. If your TSH level increases rather than decreases when you start seaweed supplementation then ask your doctor for a full spectrum of tests. As long as your thyroid hormones remain stable or improve, the TSH increase is not necessarily anything to be concerned about.

What further tests could be offered?

If your doctor has only run tests for TSH and FT4, they will probably now ask for tests for Free T3 (FT3), Reverse T3, and thyroid antibodies. If not, check that you’ve had these tests done and if not then it is worth asking for them to be carried out.

Taking levothyroxine

If your thyroid has become permanently underactive or damaged, you will have to take a thyroid hormone replacement. In the UK, the Royal College of Physicians only recommends levothyroxine which replaces T4. If you wish to try desiccated pig thyroid (Armour), which some people prefer, you will need to purchase it yourself.

When your doctor gives you levothyroxine (a thyroid hormone replacement), or makes a change to your dose, you should wait one to two months for the drug to work consistently before testing your TSH again.

It is important that when you start treatment that you do not change your diet. To suddenly withdraw seaweed and return to a diet lacking in sufficient iodine is only going to compound the issue. Unless your doctor suspects that you have an iodine sensitivity, keep taking your seaweed supplement as this is supporting your baseline health.

*Non-organic milk is higher in iodine than organic milk, because iodine is an ingredient in the disinfectant used in modern dairy milking practices and gets into the milk.

†Seaweed can sometimes, in individuals with extreme iodine sensitivity caused by conditions such as Hashimoto’s disease, lower TSH results toward overactivity (hyperthyroidism) and may have to be withdrawn on advice of a doctor. However, chelated iodine in seaweed is not absorbed in the same way as potassium iodide and some people with Hashimoto’s disease are not sensitive to the iodine in seaweed.


1. Combet E, Ma ZF, Cousins F, Thompson B, Lean ME. (2014). Low-level seaweed supplementation improves iodine status in iodine-insufficient women. Br J Nutr. 1-9. PubMed PMID: 25006699.

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