The human body needs iodine to make the thyroid hormone. This hormone is critically important during foetal development, infancy, and childhood, for the brain and nervous system to develop normally. Later in life, the thyroid hormone controls metabolism. Adults who don’t take in enough iodine can develop a goitre (a swelling of the thyroid gland in the neck), and the low output of thyroid hormone can lead to sluggish metabolism, poor thinking skills, infertility, thyroid cancer, and other conditions. It is thought that iodine deficiency is the most common cause of hypothyroidism worldwide.

Tiredness and weakness are common symptoms of iodine deficiency. In fact, some studies have found that nearly 80% of people with an iodine deficiency feel tired, sluggish and weak. This is because iodine is needed to make thyroid hormones and when thyroid hormone levels are low, the body can’t make as much energy as it usually does. This may cause your energy levels to plummet and leave you feeling weak. Tiredness and weakness appear to be the most common symptoms among those with low or slightly low thyroid hormone levels.

It should be noted that perchorlate, in large amounts, has the ability to interfere with with iodine uptake. Although not currently demonstrated in humans, it is anticipated that people exposed to excessive amounts of perchlorate for a long time may develop a decreased production of thyroid hormones. In addition, other naturally occurring chemicals, such as thiocyanate (in food and cigarette smoke) and nitrate (in some foods), are also known to interfere with iodine absorption.

High intakes of iodine can cause some of the same symptoms as iodine deficiency – including goitre, elevated levels of thyroid stimulating hormone, and hypothyroidism. Iodine-induced hyperthyroidism can also result from high iodine intakes, usually when iodine is taken to treat iodine deficiency. Studies have also shown that excessive iodine intakes cause thyroiditis and thyroid papillary cancer. Cases of acute iodine poisoning are rare and are usually caused by doses of many grams.

The recommended daily intake for iodine depends on age and life stage (taken from the US National Institutes of Health – Office of Dietary Supplements):
Birth to 6 months – 110 mcg*
7–12 months – 130 mcg*
1–3 years – 90 mcg
4–8 years – 90 mcg
9–13 years – 120 mcg
14–18 years – 150 mcg
19+ years – 150 mcg
Pregnancy – 220 mcg
Breastfeeding – 220 mcg

  • Adequate Intake

The World Health Organization, United Nations Children’s Fund and the International Council for the Control of Iodine Deficiency Disorders recommend a slightly higher iodine intake for pregnant women of 220-250 mcg per day.

Most foods are relatively low in iodine content. To ensure that everyone has a sufficient intake of iodine, WHO and UNICEF recommend universal salt iodization as a global strategy. Evidence suggests that in settings where universal salt iodization is not fully implemented, pregnant and lactating women and children under two years of age may not be receiving adequate amounts of iodized salt.

According to the World Health Organisation the UK is now among the top ten iodine-deficient countries worldwide.

This is because the NHS current position is that individuals should be able to get all the iodine they need by eating a varied and balanced diet and salt iodization has not been implemented. The NHS instead recommends the consumption of fish and shellfish and also states that iodine can be found in plant foods, such as cereals and grains. However, the amount of iodine in plant foods will vary depending and depends on the amount of iodine in the soil where the plants are grown. In addition, it should be noted that iodine losses can occur in cooking.

Some websites promote egg yolks as having a high concentration of iodine as iodine is frequently added to chicken feed but of course since the content of iodine in chicken feed can vary, the amount found in eggs can also vary.

Milk and dairy products are the main source of iodine for many people. Winter milk can have a higher iodine concentration than summer milk due to iodine supplements in winter feed. Research coming out of the UK has also shown that organic milk has a 35-50% lower iodine content than conventional milk.

In 2011 a survey of more than 700 teenage girls in the UK was published which found that two-thirds of teenage girls had mild-to-moderate iodine deficiency and that a small number had very low levels of iodine. This was thought to be partly due to low milk consumption.

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