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Low thyroid function, also known as an underactive thyroid, or hypothyroidism, is a condition in which your thyroid gland doesn't produce enough of certain hormones, such as thyroxine (T4) and triiodothyronine (T3). It releases these thyroid hormones, which control the growth and metabolism of essentially every part of your body.
The thyroid gland is controlled by the pituitary gland in the brain, which regulates the release of thyroid-stimulating hormone (TSH). TSH is the signal to the thyroid gland to release thyroid hormone. In the case of hypothyroidism, more TSH is produced, but the thyroid gland can't release more thyroid hormone in response. Hypothyroidism can also occur when there are limited or weak TSH signals sent to the gland, also resulting in reduced hormone being released.
Hypothyroidism can cause symptoms, although some early signs of an underactive thyroid are unclear, which if left untreated can cause various health problems. Thyroid problems increase with age and women are more likely to be affected by the disorder than men.
Thyroid hormone is responsible for multiple functions in the body, such as coordinating energy, growth and metabolism. The signs and symptoms of hypothyroidism vary, depending on the severity of the hormone deficiency. Problems tend to develop slowly, often over a number of years. The following are common symptoms of low thyroid function:
One of the most common symptoms of hypothyroidism is fatigue, or the feeling of tiredness. The thyroid gland controls energy balance and can influence whether you feel energised, or fatigued. The thyroid receives signals depending on what else is going on in the body and coordinates changes to function accordingly.
People with low thyroid hormones may feel exhausted and sluggish, while people with high levels of the hormone will feel jittery and nervous. Studies have shown that those with hypothyroidism feel physically and mentally exhausted and low motivation, with some reporting feeling so exhausted that they are unable to go about their day as usual. Low-thyroid individuals feel unrested, even though they may be sleeping more. Feeling sleepier than usual without a good explanation could be a sign of hypothyroidism.
Weight gain is another primary symptom of hypothyroidism. Thyroid hormones regulate body weight and food intake, and the metabolism of fat and sugar. With low levels of the hormone comes weight gain and an increase in BMI. This can even occur in mild cases, with excess weight being added to the stomach and the face.
Weight gain can occur unexpectedly. Weight gain can be a result of individuals with the condition moving less, as well as the body storing more fat - this can happen in states of low metabolism. In states of low thyroid levels, metabolism causes your body to start to store more calories from the diet as fat, instead of burning calories for energy and growth. This leads to reduced basal metabolic rates, the energy needed at rest. Unfortunately, the amount you eat will not help, with maintained calorie intake still leading to excess weight gain.
Unexpected weight gain is not always caused by an underactive thyroid, and may be a sign of other conditions. It is always important to consider lifestyle factors first.
It is common for hypothyroidism to be linked with changes in mood., like depression, anxiety, reduced concentration and more. These symptoms can occur because the brain requires thyroid hormones to function correctly. Research shows that low levels of thyroid hormones can actually alter the structure and functioning of the brain.
Hypothyroidism is associated with depression, although the reasoning is unclear. In some studies, thyroid replacement treatment improved symptoms of depression in those with mild hypothyroidism. Anxiety has also been reported with hypothyroidism. Both conditions are thought to have arisen due to the lack of energy in the brain and decrease of health.
Feeling depressed is a medical problem, so don’t hesitate to talk to your GP or therapist. Depression is not always linked with hypothyroidism, but talking to your doctor will help you cope with the problem and the causes.
With slowed metabolism comes a drop in core body temperature. Heat is a byproduct of metabolism, so people with low thyroid activity may feel cold all the time or have a low tolerance to the cold. Cold hands and feet are often reported, although they may feel their whole body is cold.
Because the amount of calories burned diminishes and your basal metabolic rate is reduced, the amount of heat generated is less. If you've noticed constant feelings of coldness, this could be a sign of hypothyroidism.