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Underactive thyroid

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The mineral iodine is critical to healthy thyroid function. A lack of it can cause low energy, weight gain, depression, muscle pain, coldness, constipation, heart disease, cognitive decline, and a variety of cancers. And for unborn babies, a lack ...


Tired All The Time?
Seaweed and your thyroid

We discuss the effect that a lack of iodine has on your thyroid over time.

From the talk by Monica Wilde: 'Tired and over 40? Seaweed and your thyroid'
at the Royal Botanic Garden Edinburgh, 15/16 September 2013. Updated July 2014

The mineral iodine is critical to healthy thyroid function. A lack of it can cause low energy, weight gain, depression, muscle pain, coldness, constipation, heart disease, cognitive decline, and a variety of cancers. And for unborn babies, a lack of iodine in their mothers can lead to poor mental abilities, cretinism and autism. 

Did you know that the World Health Organisation (WHO) has declared that the UK has a national problem of iodine insufficiency? We are just not getting enough iodine into our bodies to remain healthy.

  • 2 billion people worldwide have insufficient iodine intake (de Benoit et al., 2007)
  • 76% of British teenage school girls and 66% of adult women test as iodine insufficient (Vanderpump et al., 2011)
  • 52% of students aged 25 tested as iodine insufficient (Combet et al., 2014)
  • 49% babies are mildly iodine insufficient (Skeaff et al., 2005)  
  • Even mild iodine deficiency during pregnancy has an irreversible impact on children’s educational outcomes in the first 9 years of life (Hynes et al., 2013)  
  • British researchers say that iodine deficiency in pregnant women in the UK should be treated as an important public health issue (Bath et al., 2013)   
  • In 2006, 12 million prescriptions for levothyroxine (50 μg or 100 μg tablets) were dispensed in England, equivalent to about 1.6 million people taking long term thyroid replacement therapy, about 3% of the population (Vaidya & Pearce, 2008)

What is the thyroid gland?

The thyroid gland is situated in the neck just below the Adam’s apple. It is part of the endocrine system and it has several critical functions:

  • To control growth and development in early life (especially cognitive)
  • To control the body’s metabolism (the rate at which your body’s chemistry functions)
  • To regulate cardiovascular function ~ how your heart works (Klein & Ojamaa, 2001)
  • To maintain homeostasis ~ body temperature (Warner & MiDag, 2012)

What does the thyroid gland do?

The thyroid gland uses iodine from your diet and produces three hormones responsible for controlling metabolic rate and promoting healthy growth and development.

  • Thyroxine (T4), a pro-hormone, which converts to T3 in the body 
  • Triiodothyronine (T3) which is required by all the body’s cells and tissues  
  • Calcitonin which works with parathyroid (PTH) hormone to maintain blood calcium levels 

What is underactive thyroid ~ Hypothyroidism?

Hypothyroidism is the condition where the thyroid gland does not produce enough thyroid hormones. This causes the body’s metabolism to run too slowly and imbalances in your body’s functions, such as homeostasis, occur.

The signs of underactive thyroid

Classic early symptoms of hypothyroidism include

  • decreased energy
  • difficulty losing weight
  • dry skin
  • thinning hair
  • constipation
  • slow heart rate
  • feeling cold all the time
  • muscle aches and pains
  • forgetfulness and cognitive decline 

What happens if I don’t look after my thyroid?

If you do not have sufficient iodine in your diet, over time you can develop an underactive thyroid. If this is not corrected it can lead to problems such as:

  • obesity 
  • goitre (de Benoist, McLean, Andersson & Rogers, 2008)  
  • melancholic depression (Davis & Tremont, 2007)  
  • dementia (Bono & al., 2004) 
  • infertility (Arojoki et al., 2000)  
  • cardiovascular problems (Klein & Ojamaa, 2001)  
  • homeostatic imbalance (Warner & Mittag, 2012)
  • diabetes (Chidakel, Mentuccia & Celi, 2005) 
  • mortality in high risk groups (e.g. dialysis patients)

There is also conclusive evidence that even mild iodine deficiency during pregnancy can have long-term negative impacts on the cognitive development of babies that is not improved by iodine correction during childhood (Hynes et al., 2013). 

Autism in children is also four times more likely if the mother had a weakened thyroid gland while pregnant (Román et al., 2013).

What causes an underactive thyroid?

  • Insufficient iodine in your diet. This leads to not enough thyroid stimulating hormone (TSH) and thyroid hormones (T3, T4) being made. 
  • An auto-immune disease such as Hashimoto’s thyroiditis  
  • Having no thyroid or a damaged thyroid (for example after radiotherapy or an operation) 

What is iodine?

Iodine is a mineral needed by our bodies to make our thyroid gland function properly. It can be found naturally (chelated iodine) in seaweeds, ocean fish and in milk. It can also be manufactured (potassium iodide) and added to salt or iodine supplements.

How do I treat an underactive thyroid?

Prevention is better than cure! Ensure that you have sufficient iodine in your diet to prevent your thyroid becoming undernourished and run down.

If you leave it too late to correct your iodine deficiency, or your underactive thyroid is caused by a disease or mechanical malfunction, you may need to take the drug levothyroxine sodium everyday for the rest of your life. This is currently the only treatment recommended by the Royal College of Physicians (2011). Your doctor can give you tests to find out whether your thyroid is underactive and help you determine the correct cause of treatment.

If your thyroid is borderline, or you have the symptoms and your tests are in the ‘normal’ range, you may find that increasing your consumption of iodine makes a big difference.

Where do I get iodine from?

Iodine is not often found in the soil so not found in many vegetables. It is chiefly found in the sea and produced in milk by mammals, as it is vital to the growth and healthy development of their young.

Excellent sources of iodine include:

  • Seaweeds 
  • Ocean fish 

Other sources of iodine include:

  • Milk 
  • Eggs
  • Some fortified cereals  or multivitamins

But not everyone eats enough fish or likes the taste of seaweed. So seaweed can be taken as a supplement. You can add the powder to foods or take a capsule.

Is iodine safe?

Too much iodine can over stimulate the thyroid leading to an overactive thyroid. In some people this can trigger damage to the thyroid. However, different types of iodine behave differently in the body. It is important to choose the right type of iodine and take the right amount.

Importantly, there are two main types of iodine. Potassium iodide (found in salt and supplements like Iodoral) and chelated iodine found naturally in seaweeds like kelps and wracks.

  • Potassium iodide is absorbed by the body very quickly and excreted again within three hours. This can cause short, sharp iodine spikes in the body. There are some concerns in countries with iodised salt programs that people in these areas can end up with overactive thyroids or autoimmune disease (Teng et al., 2011).
  • Chelated (natural) iodine is absorbed by the body slowly and excreted over the next three days. This creates a much more stable, steady supply of iodine for the thyroid.

So which iodine is better? 

Practitioners at Napiers the Herbalists recommend chelated iodine because it is more consistent, stable and safer in the body avoiding the spikes associated with iodide supplements. And potassium iodide in salt is not good as too much salt in your diet can lead to high blood pressure.

Napiers Seagreens Organic Hebridean Kelp Capsules contain a Soil Association certified organic, low temperature dried seaweed called Ascophyllum nodosum. Organic is important here because the sea can sometimes be a source of pollution from sewage or heavy metals. It also ensures that the seaweed is sustainably harvested and no damage done to the seabed or to marine life. Napiers is a member of the Seaweed Health Foundation and conducts research into this essential plant.

What is the right amount? 

One 500 g capsule of certified Napiers Seagreens Organic Hebridean Kelp Capsules contains 350 mcg of chelated iodine. It also contains a host of other vitamins, minerals, amino acids, nutrients including magnesium that the body needs to successfully utilise the iodine. Kelp is a complete food.

In the research (Combet, 2014), volunteers were asked to take one capsule of Napiers Seagreens Organic Hebridean Kelp a day. The researchers measured their urine, blood and iodine levels. At the beginning they found that 52% of the group (average age 25 years old) were iodine insufficient. By the end of the study period they found that:

  • chelated iodine found in knotted kelp increases urinary iodine within safe levels  
  • it corrected thyroid stimulating hormone (TSH) production to normal levels  
  • the matrix structure of seaweed delays iodine absorption avoiding sharp peaks  
  • this matrix enables a more sustained release of iodine over a 3 day period 

From this, we at Napiers concluded that: 

  • sufficient iodine intake may prevent the development of hypothyroidism in some cases  
  • sufficient iodine intake may reverse symptoms of hypothyroidism in some cases
  • the slow, stable release of chelated iodine is a safer form of iodine supplementation 

What is the recommended dose?

The recommended daily dose in the UK is 140 mcg a day. (Micrograms are also sometimes expressed as ug.)

This is a low intake compared to countries such as Japan, where seaweed is a regular part of the diet. The average Japanese person consumes iodine in ranges from 5,280 to 13,800 mcg of iodine, with no harmful effects and a host of benefits.

WHO and UNICEF both recommend that pregnant women take a minimum of 250mcg of iodine a day (Azizi & Smyth, 2009).

Safe upper daily limits have been established as:

  • 1100 mcg World Health Organisation recommended safe upper limit 
  • 1100 mcg US Department of Medicine recommended safe upper limit
  • 1000 mcg UK Department of Health recommended max daily intake

One Napiers Seagreens Organic Hebridean Kelp capsule delivers 350 mcg of chelated iodine. You can take up to 3 capsules a day (equivalent to 1050 mcg iodine) and still be within the World Health Organisation recommended safe upper limit of 1100 mcg. And remember, that seaweed iodine is far gentler than potassium iodide supplements.

As 37% is excreted within 24 hours, three capsules will give an overall dosage after 24 hours of 662 mcg. This is why we have heard reports of people taking large doses, such as 6 capsules a day, and experiencing radical improvements to health conditions such as arthritis or skin problems without any ill effects.

I have a good diet, do I need a supplement?

The chances are that even if you have a good diet, unless you eat a lot of sea fish and seaweed, that you can still be iodine deficient. Other chemicals near iodine in the periodic table, such as chlorine and fluoride, displace iodine, so fluoride toothpaste and oral products and chlorinated water can interfere with the absorption of iodine from your diet.

A Danish study also found that women taking just iodised salt were not protected as well as those who took an iodine supplement (Andersen et al., 2013) nor if they took a multivitamin with only 150mcg iodine (Vandevijvere et al., 2013) which is the current British recommended daily allowance (RDA). Napiers Seagreens Organic Hebridean Kelp contains 350mcg per capsule.

Official Health Claims

The following claims have been approved in the EU Supplements Directive:

  • Iodine contributes to the normal production of thyroid hormones and normal thyroid function 
  • Iodine contributes to normal cognitive function (e.g. thinking, problem solving and memory skills) 
  • Iodine contributes to normal energy yielding metabolism 
  • Iodine contributes to the maintenance of normal skin 
  • Iodine contributes to normal functioning of the nervous system

Many 'man made' vitamins and minerals are not easily absorbed by the body so it is important to get them from natural sources that our body can digest. Seaweed is a whole, complete food that mankind has eaten since the dawn of time and perfectly suited to our bodies.

Nutrient profile

Napiers Seagreens Organic Hebridean Kelp contains the following phytonutrients:

  • Vitamins: A (antioxidant), B group (including B12, Thiamine, Riboflavin, Niacin, Pantothenic acid, Pyridoxin, Choline and Cobalamin), C (antioxidant), D (Cholecalciferol), E (antioxidant), H (Biotin) and K (Menadione).
  • Minerals: Calcium, Magnesium, Nitrogen, Phosphorus, Potassium, Sodium, Sulphur.
  • Amino acids: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine, Alanine, Arganine, Aspartic acid, Cysteine, Glutamic acid, Glycine, Proline, Serine, Tyrosine.
  • Trace elements: Antimony, Boron, Cobalt, Copper, Fluorine, Germanium, Gold, Iodine, Iridium, Iron, Lithium, Manganese, Molybdenum, Platinum, Rubidium, Selenium, Silicon, Silver, Tellurium, Titanium, Vanadium and Zinc.

For exact amounts visit the Napiers Seagreens Organic Hebridean Kelp page.

With busy lifestyles we don't always get the nutrition we need from our diet. Under-nourishing the body, without all the nutrients it needs, can be at the bottom of a lot of health conditions from fatigue, to digestive problems and even joint pain.

Why Sustainable? Why Organic?

Many cheap commercial kelps are heated so high in the drying process, that little goodness remains. Our Napiers Seagreens Organic Hebridean Kelp is over 60% higher in all tested vitamins and minerals and contains over 60% less silica (sand!) than comparative industrially produced kelps. It is certified by the Soil Association and is free of environmental contaminants, toxic metals and microbial pathogens, to HACCP and GMP manufacturing standards and EU and USA Biodynamic® standards.

Our pure wild organic seaweed is sustainably harvested from the clear waters off the remote conservation islands of the Outer Hebrides. This method of harvesting and drying is essential in:

  • preserving the ocean - it doesn't strip out all life from the sea bed
  • maintaining purity - not contaminated with metals or effluent
  • maintaining all nutrients - through gentle drying of the seaweed

With Napiers Seagreens Organic Hebridean Kelp capsules you know exactly what you are getting.


At Napiers, our experience is that:

  1. A leading cause of hypothyroidism is iodine insufficiency in the diet
  2. Treating low levels of T4, without treating the underlying iodine insufficiency, does not make sense. This is because levothyroxine drug monotherapy does not restore a normal thyroid state in all tissues (Celi et al., 2011) 
  3. Although levothyroxine is reasonably well-tolerated, some patients do experience side effects, especially when on multiple medications, and it is a difficult drug to manufacture with consistency (MHRA, 2013) 
  4. Knotted kelp may correct urinary iodine insufficiency and rebalance TSH (Combet, 2013) 
  5. Safe iodine supplementation is necessary for optimum thyroid baseline health and to prevent the development of longer term health problems 
  6. Levothyroxine treatment should be used to treat further T4 insufficiency once a person’s iodine intake is shown to be sufficient.

Our experience in many cases, is that treating iodine deficiency by taking a seaweed dietary supplement, restores low TSH production to normal making medication unnecessary.

If the nation had a calcium deficiency of this magnitude, affecting over half the population, would we be advising people to drink more milk and eat more dairy products, or would we keep quiet and let their health deteriorate until they needed medication?

One a day, Napiers Seagreens Organic Hebridean Kelp Capsules are the answer to ensuring you have enough daily iodine to keep your thyroid healthy!

About the Author: Monica Wilde is a director of Napiers (Rickard Lane’s) with both a commercial interest in this subject and a personal interest - coming from a family with several generations of underactive thyroid. The iodine bioavailability study was funded by the Technology Strategy Board and implemented for Napiers by the University of Glasgow. 


  1. Andersen, S.L., Sørensen, L.K., Krejbjerg, A., Møller, M., & Laurberg, P. (2013). Iodine deficiency in Danish pregnant women. Danish Medical Journal, 60(7), A4657. 

  2. Bath, S.C., Steer, C.D., Golding, J., Emmett, P., Rayman, M.P. (2013). Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet, 382(9889), 331-7. Bolton, S. (2005). Bioequivalence studies for levothyroxine. AAPS J, 7(1), 47-53. 

  3. 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.

  4. de Benoist B., McLean, E., Andersson, M., & Rogers, L. (2008). Iodine deficiency in 2007: Global progress since 1993. Food and Nutrition Bulletin, 29(3), 195-202. 

  5. Gow, S, Caldwell, G., Toft, A, et al. (1987). Relationship between pituitary and other target organ responsiveness in hypothyroid patients receiving thyroxine replacement. J Clin Endocrinol Metab, 64, 364-370. 

  6. Hynes, K.L., Otahal, P., Hay, I., & Burgess, J.R. (2013). Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort. J Clin Endocrinol Metab, 98(5), 1954-62. 

  7. John-Kalarickal, J., Pearlman, G., & Carlson, H.E. (2007). New medications which decrease levothyroxine absorption. Thyroid, 17(8), 763-5. 

  8. Román, G.C., Ghassabian, A., Bongers-Schokking, J.J., Jaddoe, V.W., Hofman, A., de Rijke, Y.B., Verhulst, F.C., & Tiemeier, H. (2013). Association of gestational maternal hypothyroxinemia and increased autism risk. Ann Neurol, Aug 13. doi: 10.1002/ana.23976. 

  9. Saranac, L., Zivanovic, S., Bjelakovic, B., Stamenkovic, H., Novak, M., & Kamenov, B. (2011). "Why is the Thyroid So Prone to Autoimmune Disease?" Hormone Research in Paediatrics, 75 (3), 157–65. 

  10. Singh, N., Singh, P.N., & Hershman, J.M. (2000). Effect of calcium carbonate on the absorption of levothyroxine. JAMA, 283(21), 2822-5. 

  11. Teng, X., Shan, Z., Chen, Y., Lai, Y., Yu, J., Shan, L., Bai, X., Li, Y., Li, N., Li, Z., Wang, S., Xing, Q., Xue, H., Zhu, L., Hou, X., Fan, C., & Teng, W. (2011). More than adequate iodine intake may increase subclinical hypothyroidism and autoimmune thyroiditis: a cross-sectional study based on two Chinese communities with different iodine intake levels. Eur J Endocrinol. 164(6):943-50. 

  12. Vaidya, B. and Pearce, S. (2008). Management of hypothyroidism in adults. British Medical Journal 337(a801). 

  13. Vanderpump, M.P., Lazarus, J.H., Smyth, P.P., Laurberg, P., Holder, R.L., Boelaert, K., & Franklyn, J.A; British Thyroid Association UK Iodine Survey Group. (2011). Iodine status of UK schoolgirls: a cross-sectional survey. Lancet. 377(9782), 2007-12. 

  14. Vanderpump, M., Tunbridge, W., French, J. et al. (1995). The incidence of thyroid disorders in the community; a twenty-year follow up of the Whickham survey. Clin Endocrinol. 43, 55-68. 

  15. Vandevijvere, S., Amsalkhir, S., Mourri, A.B., Van Oyen, H., & Moreno-Reyes, R. (2013). Iodine deficiency among Belgian pregnant women not fully corrected by iodine-containing multivitamins: a national cross-sectional survey. Br J Nutr. 109(12), 2276-84.

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