Deep tiredness, weight creeping up, feeling cold when others are comfortable, dry skin and low mood each have a dozen possible causes, but together they are the classic picture of a thyroid that has slowed down. It is worth knowing about, because it is one of the more common and most treatable reasons behind exactly this kind of run-down feeling.
The thyroid is a small, butterfly-shaped gland at the front of the neck that makes hormones acting like the body's speed control, setting how fast many systems run, including energy use, heart rate, digestion and temperature. When it is underactive, which doctors call hypothyroidism, it makes too little of these hormones and the whole body idles slower, which is why the symptoms are so wide-ranging.
Common signs include persistent tiredness, weight gain, feeling cold, dry skin, constipation and low mood. Because these are vague and shared with many other conditions, the U.S. National Institute of Diabetes and Digestive and Kidney Diseases notes that the only reliable way to know is a simple blood test that a doctor can arrange, rather than guessing from symptoms.
It becomes more common with age, is more common in women, and can run in families, and it can also follow certain other conditions or treatments. It matters especially around pregnancy or when planning one, since thyroid levels are particularly important then and need proper medical attention.
The genuinely good news is that it is very treatable. When treatment is needed it usually involves a daily tablet that replaces the missing hormone, with follow-up blood tests to get the dose right, and many people feel steadily better once levels are corrected. The dose can need adjusting over time, so staying in touch with your doctor and not stopping the tablet on your own are part of good care.