A plain-English guide to cortisol, thyroid, insulin, estrogen and testosterone, and how they affect each other.
Aug 26, 2026
8 min read
Dr. Claire Whitfield
Hormones seldom act up on their own. Read one alone and you get a number; read five together and you get an explanation. Here are the ones we run first, and what each one is really telling you.
Cortisol, thyroid and insulin
Cortisol should be high in the morning and low at night; the curve matters more than any one value, which is why we measure it twice. Thyroid sets the pace under everything, and TSH alone misses the picture without free T3 and T4. Insulin is the earliest sign of metabolic drift, often off years before glucose is.
Estradiol and testosterone
Both decline with age, both affect mood, sleep, strength and libido in every body, and both need context: where you are in your cycle, when you were drawn, how you trained that week. Without that context the number means very little.
The practical lesson: test them together, at the right time, and retest before drawing conclusions from any single reading.
Dr. Claire Whitfield
Endocrinologist, Tinsdale
