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Dr. Sarah Jarvis' health & wellness blog on Patient.co.uk

What’s metabolism? Your thyroid gland and you

An under or overactive thyroid can have profound effects on your body

Sitting on the front of our necks is a little bow tie – or at least, that’s what you would see if you looked beneath the skin. Most of us never give a thought to this gland, the Thyroid – but the hormones it produces can influence every bit of your body. Here’s how to tell if it’s showing the strain.

Your metabolism is the rate at which your body burns up energy, or ‘ticks over’. Some of the factors that affect your metabolism include:

  • How much you exercise. Exercise obviously burns calories, but it can actually speed up your resting metabolism for some hours after you stop, too.
  • Your size. The bigger you are, the more energy your cells need to keep them going, so most heavier people need more calories, compared with thin people, to stay the same weight.
  • Your muscle mass. The fitter you are, the more muscle you have – and muscle burns up energy at rest faster than fat. Being fit really does help to keep you thin!

Where does the thyroid gland fit in?

Your thyroid gland produces a hormone called thyroxine. Many of the cells in your body are controlled, in terms of how fast they tick over, by thyroxine. Usually your body’s production of thyroxine is kept within strict limits by a complicated ‘negative feedback’ system involving other hormones. If your body is ticking over too fast, your thyroid gets messages telling it to cut back on its production of thyroxine; if it’s too slow, the same hormones tell your thyroid gland to work harder. But why does it sometimes go wrong?

Underactive thyroid (hypothyroidism)

Up to one in 50 women are affected by this condition and it gets more common as you get older. Only about 1 in 1,000 men are affected. Many of your body’s natural functions slow down, and common symptoms include:

  • Tiredness.
  • Putting on weight, even if you’re not eating more.
  • Constipation and fluid retention.
  • Feeling the cold.
  • Mental slowing.
  • Dry skin and coarse hair.
  • Fluid retention.
  • Depression.

Less common symptoms include:

  • Memory loss or confusion, especially if you’re older.
  • Irregular or heavy periods.
  • Problems getting pregnant.
  • Hoarse voice.
  • Enlargement of the thyroid gland.

What causes it?

Worldwide, the most common cause of hypothyroidism is a lack of iodine (one of the components of thyroxine) in the diet. In most of the Western world, however, the main cause is inflammation of the thyroid, often caused by an autoimmune response (in which your body’s immune system, which usually protects you against infection, turns on itself). Having a history (either yourself or in close family members) of other autoimmune conditions increases your risk of getting hypothyroidism. These include vitiligo, pernicious anaemia, Addison's disease, type 1 diabetes, premature ovarian failure, coeliac disease and Sjögren's syndrome. People who have Down’s syndrome or Turner syndrome are also more likely to develop hypothyroidism, and some doctors recommend that all people with Down's syndrome should have an annual blood test to screen for it. Some medications, including lithium (used for mental health problems ) and amiodarone (used for heart rhythm abnormalities) also increase your risk.

How is it treated?

If you have an underactive thyroid, you’ll probably need to take tablets for life to top up your body’s thyroxine levels. The usual dose is 50 to 150 micrograms a day. For most people, this settles the problem quickly and completely, as long as you keep taking them. You’ll need blood tests at least once a year once your levels are stable, but once every couple of months while you and your doctor find the right dose for you.

Overactive thyroid

About 1 in 50 women are affected by overactive thyroid (also called hyperthyroidism or thyrotoxicosis) in a lifetime, mostly in their 20s-40s. Symptoms include:

  • Feeling anxious, restless and irritable.
  • Trembling and palpitations.
  • Losing weight but feeling more hungry.
  • Feeling the heat.
  • Diarrhoea.
  • Sometimes eye problems, including bulging eyes.

How is it treated?

That depends on the cause. Options include a medicine (carbimazole) usually taken for 12-18 months; surgery; or a single dose of radioactive iodine (much safer than it sounds!). Hyperthyroidism can come back, needing further courses of treatment. Your thyroid may also become underactive later – you’d be treated like anyone else with underactive thyroid (see above).

Alternative solutions for your thyroid

If you have an underactive or overactive thyroid, you will need to take the medicine prescribed. But try these useful tips as well:

  • In days gone by, people in some parts of the UK were short of iodine in their diets. This made the thyroid gland swell, but gave symptoms of underactive thyroid – so-called ‘Derbyshire neck’. These days, virtually nobody is short of iodine.
  • Supplements or foods high in iodine (like some seaweed) won’t help underactive thyroid, and may cause overactive thyroid.
  • If you take thyroid tablets, avoid taking them at the same time as foods or supplements high in iron – these can stop the thyroxine being absorbed properly.
  • Eat lots of fruit, vegetables and whole grains.
  • Avoid caffeine if you have an overactive thyroid.

With thanks to 'My Weekly' magazine where this article was originally published.

Posted by Dr Sarah Jarvis
Dr Sarah is unable to provide medical advice or respond directly to questions concerning your health. If you have health concerns we recommend contacting your GP.