Always tired even though you sleep enough? You’re cold while others are sweating? Gaining weight although you don’t eat more than before? Surprisingly often, this combination comes down to a small gland with a big effect: the thyroid. When it works too slowly, your whole metabolism slows down – gradually, over months, which is why it often goes unnoticed for a long time. The good news: an underactive thyroid is easy to detect and usually responds well to treatment.
Key takeaways
- With an underactive thyroid (hypothyroidism), the gland produces too little hormone – your metabolism runs on low.
- Typical symptoms: fatigue, feeling cold, weight gain, dry skin, hair loss, constipation and low mood.
- The most important screening test is the TSH level in your blood – it often flags a problem before you have clear symptoms.
- The most common cause in Germany is the autoimmune disease Hashimoto’s thyroiditis.
- Treatment with thyroid hormone is well established – most people live a completely normal life with it.
What is an underactive thyroid?
The thyroid is a butterfly-shaped gland below the voice box – hardly bigger than a walnut, but the pacemaker of your entire metabolism. Its hormones (T3 and T4) affect energy use, heartbeat, body temperature, digestion, mood and concentration. Production is controlled by the hormone TSH from the pituitary gland: if the thyroid produces too little, the TSH level rises – the brain “calls” louder for hormones, so to speak.
With an underactive thyroid (hypothyroidism), the gland no longer answers that call well enough. The body switches into energy-saving mode: everything slows down – your pulse, your digestion, your thinking, even the regrowth of skin and hair. Because this develops gradually over months, many people first blame their symptoms on stress, age or the weather.
Typical symptoms: when your body runs on low
No two people experience an underactive thyroid the same way – pay attention if several of the following signs come together and last for weeks:
- Fatigue and exhaustion: a leaden lack of drive despite enough sleep – often the first and most stubborn symptom.
- Feeling cold and sensitive to cold: you’re cold where others are comfortable; cold hands and feet are constant companions.
- Weight gain: your weight goes up even though nothing has changed about your diet or exercise.
- Dry skin and hair loss: your skin becomes rough and pale, your hair thinner and brittle – sometimes the outer eyebrows thin out, too.
- Constipation: sluggish digestion is a direct result of the slowed metabolism.
- Low mood and trouble concentrating: lack of drive, “brain fog” and forgetfulness can look very much like depression.
- Slow pulse and low blood pressure: your heart shifts down a gear, too.
- Irregular periods and trouble getting pregnant: in women, hormone balance can get out of rhythm – which is why the thyroid is part of the basic work-up.
Women are affected far more often than men, and the likelihood rises with age. During and after menopause in particular, the symptoms are often misread – so a look at the thyroid is doubly worthwhile here.
Causes: how an underactive thyroid develops
- Hashimoto’s thyroiditis: by far the most common cause. The immune system turns against the body’s own thyroid and weakens it over years – more on this in our separate Hashimoto’s guide.
- After treatments: thyroid surgery or radioactive iodine therapy can permanently reduce hormone production – this is expected and is deliberately compensated for.
- Medications: certain drugs, such as some heart or psychiatric medications, can affect thyroid function.
- Iodine deficiency: less common today, but still relevant – the thyroid needs iodine as a building block for its hormones.
Good to know: Often, a subclinical (latent) underactive thyroid is found first: the TSH level is raised, but the actual thyroid hormones are still normal. Whether to start treatment at this stage depends on your symptoms, age and circumstances – there’s no one-size-fits-all answer, but there is a good individual one.
