BIOLOGICAL RHYTHM RESEARCH, vol.36, no.4, pp.361-367, 2005 (SCI-Expanded)
Aim: To evaluate thyroid volume at the circadian nadir and peak of TSH levels. Subjects and methods: Serum TSH, fT3 and fT4 levels and thyroid volumes were measured at 08.00 am and 24.00 in 55 (20 male, 35 female) euthyroid healthy individuals. Results: Mean TSH level were significantly lower at 08.00 h than at at 24.00 h (1.951.29 vs 2.521.5 mu IU/ml, respectively; p < 0.001). Mean thyroid volume was also significantly lower at 08.00 h than at 24.00 h (15.094.97 vs. 17.383.49; p < 0.001). There was no relationship between TSH level and thyroid volume at either time point. Conclusion: Although thyroid volume and TSH levels increase at midnight compared to 08.00 h, there is no relationship between these two parameters. We suggest that thyroid volume measurements should be performed in the morning hours.