This content was last reviewed in September 2019 by Jason Webb, a registered nurse in our Health at Hand team.
Hypothyroidism – also known as an underactive thyroid – is where your thyroid gland doesn’t produce enough of the hormones that control your metabolism. This changes the way your body handles fat, which makes you more prone to weight gain. The replacement hormone is called levothyroxine.
Most people respond well to replacement hormone medication, but is also worth undertaking regular exercise and eating a healthy diet (whether you have an underactive thyroid or not).
You cannot prevent an underactive thyroid, but there are two main causes:
There are other, less common causes of hypothyroidism. These include:
The symptoms of an underactive thyroid tend to build up slowly and are quite general so it can be hard to pinpoint the condition. These include:
Other symptoms of hypothyroidism can relate more to your age. For example, older people tend to become forgetful or depressed, children may not grow and develop as quickly as others, whereas teenaged may start puberty early.
If you do not treat your underactive thyroid, you may also experience:
If you have any of these symptoms you must see your doctor as soon as possible.
It's important to get hypothyroidism diagnosed as soon as possible as the health implications can be serious.
A thyroid function test is used to accurately assess if you have an underactive thyroid. This is a blood test that measures thyroxine (T4) and thyroid-stimulating hormone (TSH) levels.
If you have a lot of TSH but not much T4 you could have an underactive thyroid.
If you have a lot of TSH but normal T4 levels you could be as risk of developing an underactive thyroid. Doctors will give you regular tests to monitor this.
If you only have mild symptoms of hypothyroidism and your levels aren’t too bad, doctors may not prescribe any treatment but will monitor your situation (unless you are pregnant or looking to get pregnant).
Hypothyroidism is usually treated with a medication called levothyroxine, which replaces the hormone your gland isn’t making.
There is usually a period of trial and error when you start taking levothyroxine as doctors adjust your dose to get it right. Once this is sorted you have an annual blood test to check your T4 and TSH levels.
There aren’t usually any side effects of taking levothyroxine. Sometimes you may experience diarrhoea, vomiting, headaches, chest pains and sweating, particularly if the dose it too high.
Sometimes you also have to be careful mixing levothyroxine with other medications. For example, there are two well recognised connections between thyroid function and statins:
Once you have commenced levothyroxine and the blood plasma levels have been checked and they are at the right therapeutic level – exercise and healthy eating should not be a barrier to weight loss.
The current government guidelines for healthy eating can be found on the NHS website. If you would like to lose weight, then you can use the free 12-week diet and exercise plan to help you lose weight using the NHS weight loss plan. On this site, you will also find an activity plan for beginners, whereby you will be using strength, running and flexibility workouts, so that you can learn new habits for developing an active lifestyle and help promote your weight loss.
If left untreated, an underactive thyroid can result in some complications occurring during pregnancy. For the mother, these include:
For the baby:
You must speak to your doctor immediately if you have an underactive thyroid and are pregnant or trying for a baby as these can be avoided if you get specialist treatment.
Hypothyroidism - NHS factsheet
Hyperthyroidism - NHS factsheet
How to lose weight well - AXA Health
Steps to becoming active your way - AXA Health
Diet and nutrition hub - AXA Health
Exercise and fitness hub - AXA Health
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