The Thyroid: The Gland That Sets Your Speed

Chapter 35 · Vihang Rahul Vasa

Most people have heard of the thyroid and could not say what it does. Here is the whole of it in one line: the thyroid sets the speed of your body.

What it is. A small gland shaped like a butterfly, sitting low in the front of the neck. It makes the hormones that decide how fast you burn food, how warm you feel, how quickly your heart beats, and how your weight, your cholesterol, and your energy behave. Turn it down and everything slows; turn it up and everything races.

Slow and fast, in plain symptoms. When the thyroid runs slow, an underactive thyroid, weight creeps up, tiredness settles in, the skin dries, the cold bites, the bowels slow, the mood sinks, and cholesterol rises. When it runs fast, an overactive thyroid, weight falls without trying, the heart races, the hands shake, sleep breaks, and the body feels wired. Both can be treated; neither can be guessed.

Why diabetes and the thyroid unsettle each other. Medical research reports that thyroid problems are more common in people with diabetes than in the general population, and that the two push on each other. A slow thyroid makes the body more resistant to insulin, so plasma glucose (blood sugar) becomes harder to control and weight harder to lose. In the other direction, years of high plasma glucose (blood sugar) and insulin resistance can disturb the way the body handles its thyroid hormones. A fast thyroid can send plasma glucose (blood sugar) swinging. And some medicines can affect thyroid results: one more reason the doctor, not the report, reads the numbers.

The thyroid and the liver. This matters more in this book than in most. Thyroid hormone is one of the signals that tells the liver to burn its fat. When the thyroid runs slow, that signal weakens, and medical research has found that people with an underactive thyroid are more likely to develop MASLD (Metabolic dysfunction–associated steatotic liver disease, liver fat linked to metabolic problems like obesity, diabetes, cholesterol or insulin resistance), and more likely to have scarring in it. If your liver is part of your story, as it is of mine, your thyroid belongs on the same page. Ask your hepatologist and your diabetologist to look at the two together.

The trap: the symptoms overlap. Tiredness, weight that will not move, dry skin, a low mood: every one of these gets blamed on “the plasma glucose (blood sugar),” and a quiet thyroid problem goes unnoticed for years. A single blood test (TSH, with T3 and T4 if the doctor asks) settles it. If the thyroid is the culprit, treatment is usually straightforward and your doctor guides it; the difference in how you feel can be large. Your doctor decides how often the test is due, and what any result means for you.

The message is simple: the thyroid sets your speed; diabetes, the liver, and the thyroid unsettle each other; and the only way to know is the test. If your sugar, your weight, or your liver are behaving badly for no reason you can find, ask your doctor one question: “Has my thyroid been checked?”

(References for this chapter, the thyroid–diabetes link and the thyroid–fatty-liver link, are listed in Appendix B.)

Illustration: Chapter 35 illustrated summary. The thyroid sets the pace.

Chapter 35 The thyroid sets the pace. Underactivity is illustrated with tiredness, cold and weight gain; overactivity with a racing heart, trembling and poor sleep. Symptoms can overlap. Diabetes and liver links, thyroid blood tests and the doctor's interpretation complete the picture.

Chapter at a glance: an AI-generated illustration to be read with the chapter, not instead of it. The people shown are not real.