You’re tired, all the time. You can’t lose weight, despite all that dieting, and everything just feels sluggish. Even your mood is dragging you down. You’ve been tested for underactive thyroid, and the good news is your thyroid is fine. The bad news is that the good news doesn’t make you feel any better. The truth is, you may have mild hypothyroidism, a condition which is off the radar, but still loaded with symptoms.
Hypothyroidism (or underactive thyroid) and mild hypothyroidism are different, but the same. Confused? Of course! So read on for clarification of this most tricky of issues.
First, a look at what the thyroid is, what it does, and why it is so important.
Anatomy of a Gland
The thyroid is a gland at the front of the neck. It oversees metabolism and is responsible for your basal metabolic rate, the rate at which you burn food at rest. Metabolic activity creates heat, so the thyroid is also responsible for maintaining body temperature. So if you don’t produce enough thyroid hormone, you may find you put on weight all too easily, and feel cold, even when it isn’t.
It all starts in the brain, which produces thyroid-stimulating hormone (TSH), which in turn stimulates the production of thyroxine (aka T4). T4 is converted to triiodothyronine (T3), its active form. Thyroid hormone is the term used to describe both these hormones together.
Symptoms of an Underactive Thyroid
Hypothyroidism is a condition whereby the thyroid simply isn’t making enough thyroid hormone. Here are a few typical symptoms:
- dry, coarse skin
- weight gain
- feeling cold
- hair loss
- brittle nails
- water retention, puffiness (oedema)
- hoarse or husky voice
- shortness of breath
- aching muscles
- slow heart rate
- loss of libido
Why Diet Matters
There are several possible causes of an underactive thyroid, not least of all diet. Here are some of the more crucial nutrients that affect thyroid function.
Iodine: thyroid fuel
Iodine is the number one thyroid nutrient, making up over half the weight of thyroid hormone. It is found in seafood, seaweed (where it was first discovered), dairy foods (not naturally; it is routinely added to cattle feed), and anything that contains iodized salt.
Iodine deficiency has serious consequences, not just for metabolism, but for growth and development. It is recognised by the World Health Organization as the most common preventable cause of brain damage in the world today.
The scale of the problem is due to the fact that most of the iodine on the planet is in the sea, not soil. During the last Ice Age, glaciation caused the iodine-rich layers of soil to wash into the sea. That is why fish and seaweed are such rich sources.
That is also why vegans and vegetarians, if they don’t eat seaweed regularly, are especially vulnerable. So too is anyone who avoids fish, which studies show is the majority of the population.
In 2011, The Lancet published a study which determined the iodine status of nearly 700 schoolgirls aged 14-15 across the UK. Urine samples were taken to measure iodine. The results showed mild deficiency in 51% of the girls, moderate deficiency in 16% and severe deficiency in 1%. If the overwhelming majority of teenage girls are iodine deficient, there is every reason to assume that so too is the majority of everyone else in the UK.
Beyond Iodine: Selenium, Iron and Zinc
The thyroid requires more than just iodine. Among the other nutrients it needs are selenium, iron and zinc.
Selenium is required for the conversion of T4 to T3. Like iodine, selenium shortage is recognised as a potentially serious issue. As long ago as 1997 an article in the British Medical Journal claimed it was ‘time to act’ on the worrying depletion of selenium levels in soil throughout the world, including Europe. Fish and seafood are the best sources, and Brazil nuts contain moderate amounts.
Deficiency of iron and zinc could also lead to underactive thyroid. Zinc is required for all hormone production, including thyroid hormone. Like selenium, it is required for the conversion of T4 to T3. Good sources include meat, especially red meat, fish and seafood.
Iron deficiency impairs thyroid metabolism by reducing levels of T4 and T3. The best source of iron is red meat. Iron from plant sources has poor bioavailability by comparison, meaning that very little is absorbed. So if you are vegetarian, it might be worth having a blood test for iron deficiency anaemia; you may have to supplement.
Testing For An Underactive Thyroid – And Why Mild Underthyoidism Goes Undetected
There are various tests which your GP can arrange; those described below are the main ones in use today.
Total thyroxine (TT4)
This test measures the amount of T4 in the blood. However, because T4 is protein-bound and therefore inactive, this is not an accurate measure of thyroid hormone. This test has largely been replaced by measurement of FT4.
Free thyroxine (FT4)
This tests the amount of free thyroxine in the blood – the thyroxine which is free to be converted to T3, the active form of thyroid hormone. It is therefore quite useful.
This is measured as free T3 (not protein bound) and total T3 (attached to a protein). Although very useful, it does not measure how much T3 actually enters the cells.
Thyroid-stimulating hormone (TSH)
This is thought to be a good measurement of either excessive or insufficient thyroid activity. A high reading indicates hypothyroidism, because the body is increasing its production and release of TSH in an effort to push up T4 levels.
Thyroid autoantibody testing
Thyroid conditions may be caused by the body failing to recognise self as self and creating antibodies against its own tissues. Hashimoto’s thyroiditis and Grave’s disease are two such conditions.
Urine iodine excretion
This is a very useful test, especially if you are vegetarian or vegan, or just avoid seafood and/or dairy produce. Urinary iodine excretion is believed to be a good indicator of dietary iodine intake. It also monitors excessive iodine intake.
The Trouble With Tests
Thyroid testing is by no means conclusive – if only a simple blood test could be that simple.
The dilemma lies in the reference range – that is, the point from A to B of the test results which is considered to be ‘normal’. All too often, when a test result comes back normal, the patient may be persuaded to stop worrying about their health problems because according to test results they haven’t got any.
You might fall within the ‘normal’ range (which is very wide, so most people do), but still have mild (subclinical) hypothyroidism.
Mild (subclinical) hypothyroidism
Subclinical hypothyroidism is defined as having raised TSH levels, but normal free thyroid hormone levels. If this is what your test results indicate, you are regarded as being in a pre-hypothyroid state. Even so, if you have mild hypothyroidism you may experience typical underactive thyroid symptoms.
More and more doctors and researchers are beginning to question the definition of “normal” with regard to the reference ranges set by laboratories to assess the level of thyroid hormones in the blood. The trouble is, different laboratories set different cut-off limits of what is considered normal.
“We, indeed, believe that subclinical hypothyroidism represents mild thyroid failure and is a clinically important disorder that has adverse clinical consequences and that should be treated in most, if not all, cases.”
Do You Have Mild Hypothyroidism?
One of the first things to consider is weight. People with mild hypothyroidism tend to gain weight easily, despite eating normally, or following a calorie-restricted diet.
What to do if you think you might have mild hypothyroidism
First, go to your GP to get tested. Remember that the reference range is a contentious, arbitrary figure. It is worth asking for a urine iodine test to determine your iodine status – if you don’t ask, you probably won’t get.
There is also a very useful home test you can try, requiring only a thermometer. The basal temperature test was first described by the famous, late Dr Broda Barnes in 1945. Although it is by no means conclusive, it can give a good indication of thyroid status, especially if you have lots of hypothyroid symptoms.
Click on the link to the Thyroid Patient Advocacy for details of how to carry out the basal tempterature test.
What Not to Do: Go on a Diet
One of the best ways to mess up your thyroid is by yo-yo dieting. Eating a calorie-restricted diet reduces your metabolic rate. Because your Stone-Age body is programmed to do its damnedest to retain fat reserves when food intake is restricted, it does. Calorie restriction causes a reduction in T3 production, and eventually you find that you have to eat less and less just to stay at the same weight. You’re paddling like fury just to stay afloat.
For more information on the effect of calorie restriction on metabolism, see the AYCE article – Step 1 for successful weight loss.
Certain foods contain substances called goitrogens, which are believed to cause underactive thyroid by blocking the conversion of T4 hormone to T3. Foods which contain goitrogens include the brassica family: kale, sprouts, cauliflower, cabbage. Other goitrogenic foods include watercress, mustard, turnips, cassava and peanuts.
As you may have noticed, a lot of people regularly eat green vegetables and other goitrogen-containing foods without developing an underactive thyroid. That’s because cooking these foods disables the goitrogens so they become harmless. Also, problems are only likely to arise where iodine is already deficient.
Finally, make sure your diet is packed with those nutrients that are so crucial to thyroid function.
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