Reviewed by: 69Fun Health Editors
Clinical Guideline Standard: ATA / AACE 2026 Reference Protocol
You take your thyroid medication faithfully every morning. Then your labs come back and the number has jumped — TSH was 1.8 mIU/L three months ago, now it’s 5.2 mIU/L. Or the reverse.
That doesn’t always mean your dose is wrong. TSH can move a lot for other biological reasons.
The Circadian Rhythm of TSH
TSH runs on a daily clock. It peaks between 2:00 AM and 4:00 AM, falls steeply in the early morning, and hits its lowest point in the late afternoon.
A fasting draw at 8:00 AM versus a draw at 2:30 PM after lunch can differ by 30% to 50% in reported TSH concentration. Same person, same dose, different hour. So book follow-up draws at the exact same hour of the morning, fasted.
Other Common Triggers of TSH Bounces
- Recent viral infections: A mild viral upper respiratory infection can trigger transient thyroiditis. Stored hormone gets released first, and temporary suppression can follow.
- Biotin interference: Multivitamins containing B7 (biotin) can distort laboratory assays. You can check the timing with our Biotin Washout Calculator.
- Seasonal shifts: TSH naturally rises in the cold winter months, as the body demands greater thermogenesis to stay warm.
Frequently Asked Questions
Q: Why does my TSH change from one test to the next?
A: Time of day, recent illness, biotin, and season can all move it. They affect thyroid hormone receptor binding, peripheral deiodinase conversion, and metabolic homeostasis, so proper timing and physician oversight matter.
Q: What should I do if my TSH keeps swinging?
A: Endocrinologists recommend comprehensive serum testing (TSH, Free T3, Free T4, and antibodies), optimizing micronutrient cofactors (selenium, zinc, ferritin), and adjusting medication spacing under direct medical supervision.
This article is for educational purposes only and is not medical advice. Please see your doctor about your own testing and treatment.