The thyroid is an incredibly important gland in your neck, around the front of your windpipe. It secretes hormones which control the rate of metabolism, in other words how quickly you burn off energy in food to produce fuel for your body.
We always take an evidence-based approach and aim to provide you with actionable knowledge and tips to help you on your journey to optimal health.
What is hypothyroidism?
Hypoyhyroidism is when your thyroid gland does not make enough thyroid hormone to support the body’s needs. It’s estimated that hypothyroidism, also known as low thyroid function or underactive thyroid disease, affects around 1-2% of the population (1).
Hypothyroidism becomes more common as people age and it affects ten times as many women as men. It often occurs first at the menopause, when symptoms may be missed because of their similarity with many other menopause symptoms.
If your thyroid is not functioning at full speed, your metabolic rate will be slower than it should be. This means you won’t be burning off energy effectively, and you may tend to gain weight. Other symptoms of an under functioning thyroid can include feeling too cold or too hot, low energy, constipation, dry skin and hair, low mood and libido, along with memory and attention problems.
Thyroid hormone regulation
The thyroid regulates your metabolism by means of a clever feedback loop. First, the hypothalamus in the brain senses a drop in thyroxine in the blood, which causes it to release thyroid releasing hormone (TRH). This causes the pituitary gland to release thyroid stimulating hormone (TSH) which tells the thyroid to release thyroxine.
There are actually two different types of thyroxine which differ in how much iodine they contain, called T4 and T3.
T3 is also known as triiodothyronine. The thyroid produces mostly T4, which can be converted into T3 as needed by removing an iodine molecule. T3 is far more active than T4 and so is better able to stimulate receptors for thyroxine, situated in the nucleus of every cell in the body.
Low thyroid function is usually diagnosed at a GP’s surgery by a blood test which will detect levels of TSH and T4. Low T4 coupled with high TSH is the accepted indicator of hypothyroidism.
If TSH is high, it suggests the pituitary is telling the thyroid to produce more thyroxine, but the thyroid gland is not able to respond or isn’t listening, resulting in low levels of T4.
Medical treatment for hypothyroidism
If hypothyroidism is detected, patients are usually prescribed a drug called levothyroxine, a synthetic version of T4. The synthetic version of T3 is called liothyronine, although this is not currently prescribed on the NHS as it’s far more expensive than levothyroxine.
According to the NHS, over 32 million prescriptions for levothyroxine were written in 2018, at a cost of over £86 million (2). In the USA in 2015, levothyroxine was the drug most commonly prescribed by GPs – a staggering 21.5 million prescriptions were issued in a single month (3).
Do the drugs work?
Hypothyroidism can be a tricky disease to treat, and many people taking levothyroxine don’t feel the benefits they expect. Research has now concluded thousands of people may be being prescribed thyroid drugs when they are not needed, because there is insufficient evidence that they help.
Researchers looked at people with sub-clinical hypothyroidism, which is mild or borderline thyroid disorder. This is diagnosed when TSH levels are elevated but T4 levels are normal.
Subclinical hypothyroidism is thought to affect between 4 and 20% of the adult UK population. It’s more common in women and the elderly. Around one third of patients do not experience any symptoms, but when symptoms are present they’re generally similar to overt hypothyroidism.
Elevated TSH levels are known to increase the likelihood of developing hypothyroidism in the future, although this risk is magnified when elevated TSH levels are accompanied by the presence of anti-thyroid antibodies (4).
Results of the study
The study involved examining the results from 21 trials, which in total involved over 2000 patients. Most of these were aged over 65 years (5).
Current medical guidelines recommend thyroid hormone prescription for adults with TSH levels above 10mlU/L of blood, regardless of T4 levels. Normal TSH levels would fall between 0.4 and 4mlU/L. It’s estimated around 90% of patients with subclinical hypothyroidism have TSH levels of between 4-10mlU/l. TSH levels naturally increase with age.
By looking at the results of the trials, the researchers found that when patients with borderline hypothyroidism were prescribed thyroxine, they did not experience an improvement in symptoms such as low mood, fatigue and weight gain. Because elevated TSH values have been linked to higher incidence of cardiovascular disease, researchers also examined this link. They concluded the medication had little or no effect on protecting people with subclinical hypothyroidism against cardiovascular disease.
Thyroxine prescription is usually long term – it’s assumed borderline hypothyroid disorders do not usually spontaneously resolve themselves on their own. The patient requires regular monitoring over the years to assess whether they are on the correct dosage. Lifelong treatment is not only expensive for the NHS, it’s also burdensome for the patient because of the monitoring required.
However, the authors of the review note that in more than 50% of cases TSH levels between 5.5mlU/L to over 10mlU/L returned to normal without medication within five years (6).
Often TSH can be elevated during a period of stress or disease, or even as a result of natural monthly female hormone fluctuations, so it follows if a patient’s circumstances change, their TSH may normalise. Despite this, in many countries prescriptions for levothyroxine are increasing year on year.
It’s now commonly being prescribed for subclinical hypothyroidism, with the drug being prescribed 1.3 times more frequently for patients with TSH levels of over 10mIU/L in 2009 than in 2001 (7). One study from Norway suggests the incidence of subclinical hypothyroidism has not increased over time, but it’s being medicated more often (8).
Why don’t the drugs work?
Perhaps the results of this trial should not be interpreted as subclinical hypothyroidism not needing treating, but that the treatment given is ineffective.
Remember the feedback loop we talked about earlier? If external T4 is given as a pill, the hypothalamus will sense the extra thyroxine in the blood and will decrease its production of TRH, in turn reducing the production of TSH by the pituitary gland. This will lead to a downward spiral in the production of thyroxine. Over time therefore patients may find their dose of levothyroxine needs to be stepped up and up to achieve a similar result.
Why is my thyroid struggling?
From a Functional Medicine perspective, high TSH levels and normal T4 levels may be occurring not because the gland is failing, but because of a number of other factors. For example, the body may be inefficient in converting T4 into the active T3.
If your thyroid is not functioning correctly, it can be useful to look at the factors which may be causing it to behave in this way. Sometimes there may be reduced availability of the raw ingredients used to make thyroid hormones, although thyroid disorder is rarely simply a lack of thyroxine. Often, nutritional and lifestyle factors may be suppressing thyroid function, or the ability of the individual body cells to listen to the message of the thyroxine may be compromised. It may even be the result of the body’s own immune system attacking the thyroid and destroying some of the thyroxine-producing cells.
However, it’s important not to stop taking thyroid medication without speaking to your GP.
Takeaway
Your thyroid, like any other part of your body, is affected by your nutritional and lifestyle choices.
If your thyroid is struggling, an experienced Personalised Health practitioner would look in detail at your personal health history to determine the underlying reasons for any thyroid dysfunction. In conjunction with this, functional medicine testing can be useful to determine your levels of T3 as well as T4, along with any thyroid antibodies, TSH levels and reverse T3, which is produced when there’s a problem converting T4 to the active form of T3. This can be down to stress or poor liver function.
It’s also useful to test the functioning of associated glands in the body such as the adrenal gland and levels of sex hormones, as these too can influence how your thyroid is functioning.
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