Thyroid Function Explained: How One Small Gland Runs You

You probably don't think much about your thyroid until a blood test shows an unusual TSH level. Suddenly, you're wondering whether it's behind your tiredness, weight changes or other symptoms. And before you know it, everyone has advice. A relative recommends certain foods, a colleague shares their experience with thyroid tablets and someone tells you to stop eating cabbage. So, what does your thyroid actually do, and why does it matter so much? Thyroid function refers to how well the small, butterfly-shaped gland at the front of your neck produces hormones that help regulate your body's energy use. According to the NIDDK, these hormones affect almost every organ, including how fast your heart beats. When thyroid hormone levels become too high or too low, you may notice changes in your energy, weight, mood and other everyday functions. Understanding how your thyroid works, what can cause problems and what your test results mean can help you separate useful medical advice from common myths.

Where is the thyroid and what does it make?

Place your fingers just below your Adam's apple and swallow. The soft tissue moving under your fingers sits right over the thyroid. It is small, yet it makes two hormones that travel to every cell in your body. They are called T4 and T3. T4 is the main hormone the gland releases. T3 is the second. Together they act like a speed setting for your cells, controlling how your body uses energy. To make these hormones, the thyroid needs iodine from your food. Iodised salt is one everyday source.

How does your body control the thyroid?

Your thyroid does not decide on its own how much hormone to release. It follows instructions from the brain, in a loop that works much like the thermostat on an air conditioner.

1. A part of the brain called the hypothalamus keeps watch on thyroid hormone levels in the blood.

2. When levels drop, it signals the pituitary, a pea-sized gland at the base of the brain.

3. The pituitary releases TSH, short for thyroid-stimulating hormone, into the blood.

4. TSH reaches the thyroid and tells it to make more T4 and T3.

5. When levels rise high enough, the brain eases off and TSH falls.

This is why doctors often look at TSH first. It is the brain's voice telling the thyroid to work harder or slow down. A high TSH usually means the brain is shouting because the thyroid is not keeping up. A low TSH usually means the thyroid is already making too much.

What happens when the thyroid slows down?

An underactive thyroid is called hypothyroidism. When there is not enough hormone, many of your body's functions slow down. Common signs listed by NIDDK include these.

• Tiredness

• Weight gain

• Feeling cold when others are comfortable

• Joint and muscle pain

• Dry skin or dry, thinning hair

• Heavy or irregular periods or difficulty getting pregnant

• A slow heart rate

• Low mood

Because hypothyroidism develops slowly, NIDDK notes that people may not notice symptoms for months or even years. The most common cause is Hashimoto's disease, in which the immune system attacks the thyroid by mistake.

What happens when it speeds up?

An overactive thyroid is called hyperthyroidism. Everything runs too fast. NIDDK lists weight loss despite a bigger appetite, a fast or irregular heartbeat, nervousness, trouble sleeping, shaky hands, sweating and trouble tolerating heat among its signs. The most common cause is Graves' disease, another condition where the immune system targets the thyroid.

How common are thyroid problems in India?

Thyroid problems are common in India. A study of 5,360 adults across eight Indian cities found that 10.95% had hypothyroidism. That is roughly one adult in every ten. A few details from that study stand out.

• About one in three of those people did not know they had it until the study tested them.

• It affected 15.86% of women compared with 5.02% of men.

• It was more common in inland cities than in coastal ones.

• Another 8.02% had subclinical hypothyroidism, where TSH is raised but T4 is still normal.

• More than one in five people had antibodies against the thyroid, a sign of the immune system targeting the gland.

The pattern matches what NIDDK reports elsewhere. Women are much more likely than men to develop hypothyroidism and it is more common after 60 and in people with a family history of thyroid disease.

Getting tested the right way

A thyroid problem cannot be diagnosed from symptoms alone, because tiredness and weight changes have many causes. A simple blood test tells the real story. NIDDK says doctors usually check TSH first and may add T4, T3 or thyroid antibody tests. A few tips help you get an accurate result.

• Tell your doctor about every supplement you take. Biotin, a B vitamin found in many supplements, is one of the known causes of interference in thyroid blood tests because of the way some of these tests work. Your doctor may ask you to pause it before the test.

• Normal ranges for TSH and free T4 vary from lab to lab. Read your result against the range printed on your own report.

• Get tested at the same lab each time if you can, so your numbers are easier to compare.

• Do not change or stop thyroid medicine before a test unless your doctor asks you to.

If you are tired all the time, low iron and low vitamin B12 are other possible causes worth checking at the same visit. Our Aora guides on iron deficiency in women and vitamin B12 deficiency explain the signs.

Living well with a thyroid condition

Thyroid problems can usually be managed with the right treatment. If you have an underactive thyroid (hypothyroidism), your doctor may prescribe levothyroxine. According to the NIDDK, this medicine replaces the hormone your thyroid isn't making enough of. It's usually taken in the morning on an empty stomach. Your doctor will check your thyroid levels again after six to eight weeks and adjust the dose if needed. Along with taking your medicine, a few everyday habits can help you manage your thyroid health.

1. Take your medicine regularly. Follow your doctor's instructions and try to take it at the same time each day. Don't change the dose or stop taking it without medical advice.

2. Use iodised salt in normal amounts. Iodine helps your thyroid produce hormones, but taking more than you need won't improve thyroid function.

3. Avoid taking extra iodine without medical advice. High-dose iodine supplements and seaweed products may worsen thyroid problems, particularly in people with Hashimoto's disease or other autoimmune thyroid conditions, as the NIDDK explains.

4. Keep up with your blood tests. Regular tests help your doctor check whether your treatment is working. This is especially important during pregnancy, when thyroid hormone needs can change.

5. Maintain healthy daily habits. Eat balanced meals with enough protein, vegetables and whole grains, and stay physically active. These habits support your overall health alongside thyroid treatment.

Symptoms such as thinning hair and irregular periods aren't always caused by thyroid problems. They can have other explanations, so it's worth discussing them with your doctor rather than assuming your thyroid is responsible. These articles on hair loss in women and PCOS and insulin resistance help you think through the other possibilities with your doctor.

When to see a doctor

Ask your doctor whether a thyroid test makes sense for you if you notice the signs above or are worried. MedlinePlus advises contacting your doctor if you have symptoms of an underactive thyroid. If you are already being treated for it, MedlinePlus advises contacting your doctor if you develop chest pain or a rapid heartbeat, if your symptoms get worse or do not improve with treatment, or if you develop new symptoms. For an overactive thyroid, MedlinePlus advises the same. It says to go to an emergency room or call the local emergency number (112 in India) if you have a change in consciousness, dizziness or a rapid, irregular heartbeat.

The quiet gland that sets your pace

Your thyroid works silently in the background every second of your life, setting the pace for your heart, your gut, your skin, your mood and your energy. When it drifts out of balance, the changes can creep in so slowly that people miss them for a long time. A single blood test can bring that hidden story into the open. Once you know, you and your doctor can work out the right treatment.

Sources

• NIDDK: Hypothyroidism (underactive thyroid)

• NIDDK: Hyperthyroidism (overactive thyroid)

• Prevalence of hypothyroidism in adults: an epidemiological study in eight cities of India (Indian Journal of Endocrinology and Metabolism, 2013)

• Interferences with thyroid function immunoassays: clinical implications and detection algorithm (Endocrine Reviews, 2018)

• Hypothyroidism (MedlinePlus Medical Encyclopedia)

• Hyperthyroidism (MedlinePlus Medical Encyclopedia)

Medical Disclaimer: This article is for general information and is not a substitute for advice from your doctor. Speak to a qualified healthcare professional before starting any supplement, especially if you are pregnant, breastfeeding or taking medication.