The thyroid gland is found wrapped around the front of your wind pipe just below the Adam's apple in your neck. It produces hormones known as thyroxine (T4) and tri-iodothyronine (T3) that have a number of effects on your body1.
- Raising the metabolic rate and in so doing increasing your consumption of oxygen. A rise in thyroid activity increases your pulse and breathing rate.
- Heating the body, which it does by stimulating your cells to continuously pump sodium into the blood and potassium into the cells against their concentration gradient. It is basically a way of generating heat without changing anything permanently in the body. People with an underactive thyroid gland get cold very easily.
- Stimulating fat burning and cholesterol excretion as well as reducing blood sugar levels. Basically the thyroid is telling the body to get into action.
- Enhancing the actions of adrenaline, leading to increased heart rate and blood pressure. People with low thyroid activity often start off with low blood pressure (hypotension). This hypotension may rise later during the course of the disease as the body adapts however.
- Stimulating growth of nervous and skeletal tissues. During childhood inadequate levels of thyroid hormones cause stunted growth and mental retardation.
The thyroid is stimulated to work by the hypothalamus and anterior pituitary, both of which are located in your head, an inch or two behind your nose and eyes. The anterior pituitary releases thyroid stimulating hormone (TSH), which stimulates the thyroid to produce T4 and a little bit of T3. The blood ratio between the two is roughly 20:1. These hormones are fat soluble, and as such don't easily travel in the bloodstream. The body combines T4 and T3 with a protein called thyroid binding globulin (TBG) in order to transport it around the body. To have good thyroid function you need adequate levels of these transport proteins.
T4 is not that active and needs to be converted into T3 in our cells in order to produce its effects. This is done by selenium containing enzymes called deiodinases. If these are not working sufficiently well, then it is possible to suffer from symptoms of low thyroid function (hypothyroid) without having anything wrong with your thyroid gland.
Hyperthyroid is an autoimmune condition in which the thyroid gland secretes too much thyroxine. From 60-90% of hyperthyroid cases are suffering from Grave's disease. Grave's disease occurs in over 1% of the population, and is at least 5 times more prevalent in females than males. It has a significant genetic component of risk - running in families and normally manifests itself in early adolescence. This causes a swelling of the neck called goiter, mood disturbances and in about 30-50% of cases also causes the eyes to bulge out in what is called Grave's opthalmopathy, proptosis or exophthalmos. Other symptoms include anxiety, insomnia and heat intolerance.
It is caused by an autoimmune reaction in which antibodies are formed by the immune system that mimic the effects of TSH on the thyroid cells. This switches the thyroid gland into overdrive. Grave's disease is considered incurable as it is not yet known how to switch off the antibodies that create the havoc. Conventional treatment centres around 3 options. Removal of the thyroid, irradiation of the thyroid to kill off part of it, and reducing the activity of the thyroid with drugs that slow down the rate of production of T4 and T3.
Grave's disease responds well to treatment, although a common complication after surgery or radiation treatment is hypothyroidism (see below). Unlike hypothyroid conditions, there is not as much interest among nutritionists in hyperthyroid conditions. This is in part due to the fact that dietary interventions are not as effective. However, there are diet and lifestyle changes that can help. Giving up smoking is important as this reduces the chance of developing bulgy eyes (exophthalmos). The rest of the diet should be based on the healthy diets recommended for most people, i.e. low GI with plenty of fish, nuts, seeds, vegetables and meat. Dairy and grain based foods to be eaten in moderation and junk foods to be minimised.
Hypothyroid is often caused by an autoimmune attack on the thyroid by the body's immune system. When this manifests itself with goiter then it is known as Hashimoto's thyroiditis and is relatively uncommon affecting 0.1-0.2% of the population. However, without the overt goiter symptoms autoimmune hypothyroid is very common, affecting about 3-5 times as many women as men, and increasing in prevalence as we get older. It affects about 10% of women and 3% of men, and if we look at women over the age of 60 it then affects about 20%. As such it must be seen as a condition of major importance to our health, and worth knowing about, as everyone of us will know someone who is affected by a sub-optimal thyroid gland.
Hypothyroid gives rise to a number of symptoms such as cold hands and feet, fatigue, weight gain, loss of hair - particularly from the eyebrows, dry flaky skin and depression. It can also lead to facial puffiness called myxoedema, pictured left, and reduced fertility. However, when it comes to classifying the disease it gets a lot more controversial than just observing the symptoms. Typically a diagnosis of hypothyroid is made when levels of TSH are high and levels of T4 are low. If the figures fall into certain ranges treatment with thyroxine is often deemed appropriate.
What hormone levels make me hypothyroid?
Here in the UK the TSH reference range is 0.4-4.5 mIU/L3. Treatment with T4 (levothyroxine) is considered by many doctors only if you are above 4.5. However in 2002 the American Association of Clinical Endocrinologists (AACE) recommended that the upper limit be reduced to 3.0. Under this definition instead of about 5% of people being classified as hypothyroid, nearly 20% would be. Given that higher levels of TSH have been associated with increased levels of cardiac related death in people between the ages of 40 and 704 perhaps this reduction in the upper limit would not be such a bad thing. Certainly more serious consideration of thyroxine treatment should be given if levels of TSH are above 3.0 and there are significant hypothyroid like symptoms.
What hypothyroid treatments are there, and are they safe?
There are two main drug based approaches to hypothyroidism. One is by using synthetic T4 (levothyroxine). The other is using dessicated thyroid glands, (Armour Thyroid) normally derived from pigs. These provide T4 and T3 and are thought by some to be more effective. In theory somebody who lacked sufficient deiodinase activity would benefit as they would not be able to convert T4 into its more active T3 form as effectively. Currently there is not firm evidence that dessicated thyroid is more effective than synthetic thyroid. This could be part of the reason that in the UK the general advice to doctors is to use synthetic thyroxine instead.
As with many drug treatments, a balance has to be struck between the benefits and the side effects. In the case of treatment with thyroid hormones one possible side effect is osteoporosis. As a rough guide if treatment leads to symptoms such as anxiety and restlessness then too much drug is probably being taken and you should consult your doctor.
Are there dietary and natural ways to improve hypothyroid?
Thyroid hormone is formed when iodine is added to an amino acid called tyrosine. Having sufficient iodine in the diet can help as long as you are not deficient in selenium. Too much iodine may inactivate the the enzyme TPO, that joins iodine to the amino acid, tyrosine to make the thyroid hormones (T4 and T3). Interestingly both iodine and tyrosine are found in large amounts in most seafood. Good example are seaweeds such as kelp and fish such as salmon. However, iodine can be displaced by other elements such as fluorine, chlorine and bromine. The implication is that it is best to avoid drinking water out of swimming pools, using too much fluoridated toothpaste and consuming any products containing bromine such as Pepsi's Mountain Dew drink. Vitamin A and iron are two micronutrients to ensure you have enough of. They both help the body process iodine. Low blood iron levels can have knock on effects on the health of the thyroid gland and so if you are on iron supplements and have hypothyroid like symptoms, it may well be worth following the dietary guidance in this section.
Selenium is another mineral that is needed by the body to ensure that hypothyroid symptoms do not occur as it is found in the enzymes that convert T4 into T3. It also plays a role in ensuring you can utilise iodine properly. Without sufficient selenium, iodine can be toxic for people with thyroid problems. Good dietary sources of selenium include meat, especially organ meats such as liver and kidney. Dairy produce also constitute a good source. Some brazil nuts also contain large amounts of selenium.
Another dietary solution is to avoid what are called goitrogens. These substances reduce the uptake of iodine by the thyroid. Known goitrogens include the brassica family of green leafy vegetables such as brocolli, kale and cabbage. If you do consume these vegetables then cooking them well will help inactivate the substances that impact on the thyroid. Spinach is from another plant family and is OK to eat. Other goitrogens include soy based products and the grain millet.
Supplements can be used in addition to dietary changes. There are various formulas that you come across.
- Glandulars are generally based on dessicated glands from mammals such as pigs or cows. They sometimes contain standardised amounts of hormones such as in "Armour Thyroid", or they may have indeterminate amounts of thyroid hormone or the hormones may have been removed. The effectiveness of glandular formulas without standard amounts of T4 and T3 in them are difficult to assess.
- Thyroid support formulas. These are designed to provide some of the nutrients that may help restore an underactive thyroid. Typically they include sources of iodine, selenium and tyrosine often with other relatively insignificant amounts of vitamins A, B and C and other amino acids.
- T4-T3 conversion formulas. These normally contain plenty of selenium and occassionally other substances such as mukul myrrh, which are associated with changes in thyroid function.
My view is that the thyroid support formulas could be helpful. The effectiveness of glandulars is difficult to assess, as what they contain is generally not clearly quantified. It is also likely that much of the content is broken down into amino acids by the stomach, and so may well be no different from consuming other protein sources. Thyroid hormones themselves are not broken down in the stomach and are effectively absorbed by the intestines, which is why the medicines T4(levothyroxine) and T3(liothronine) are taken orally.
1) Principles of Anatomy and Physiology. Tortora and Derrickson ISBN 0-471-71871-8