Circadian rhythm of TSH levels in subjects with Alzheimer's disease (AD)

Objectives The circadian rhythm of serum thyroid stimulating hormone (TSH) levels in patients with Alzheimer's disease was measured by means of a case-control study. Methods Serum samples from cases and controls were collected continuously for 2 days, and then once every 2 h ( even number time-point during the first day and odd number time-point in the second). TSH was detected by radioimmunoassay. Results AD patients had no significant circadian rhythm in serum TSH levels, whereas normal controls did. In normal controls, serum TSH levels from 19: 00 to 20: 00 were the lowest (19: 00, 3.89 +/- 0.97 mIU/L; 20: 00, 3.76 +/- 0.84 mIU/L) and those in the period 2:00-4:00 were the highest ( 2: 00, 6.15 +/- 0.94 mIU/ L; 3: 00, 6.32 +/- 1.04 mIU/L; 4: 00, 6.39 +/- 1.13 mIU/L; F = 6.762, df = 23, P = 0.002). However, in AD patients, 24-h serum TSH levels were 3.80-4.03 mIU/ L ( F = 0.897, df = 23, P = 0.996). At the 24 time-points, except for the four time-points from 16: 00 to 19: 00, TSH levels in AD patients were significantly lower than those in normal controls. Conclusions The circadian rhythm of serum TSH levels in AD patients did not appear, and their serum TSH levels were significantly lower than those in normal controls. Significance The circadian rhythm in serum TSH levels in AD patients differs greatly from that of the general population.