Absent Diurnal Variation in Serum Testosterone in Young Men with Testosterone Deficiency

Area of Science:

• Endocrinology
• Men's Health
• Circadian Biology

Background:

• Healthy young men typically display a diurnal pattern in serum testosterone levels.
• Limited data exists on the diurnal variation of testosterone in men with diagnosed testosterone deficiency.

Purpose of the Study:

• To investigate the diurnal variation of serum testosterone in young men with and without testosterone deficiency.
• To compare testosterone level fluctuations over a 24-hour period between these two groups.

Main Methods:

• 21 male volunteers (mean age 31.7 years) were studied over 24 hours.
• Blood samples were collected at multiple time points: 8 a.m., 11 a.m., 2 p.m., 5 p.m., 8 p.m., and 8 a.m. the next day.
• Men were classified as having normal or low testosterone based on 8 a.m. serum levels (>300 ng/dl or <300 ng/dl, respectively).

Main Results:

• Overall mean testosterone peaked at 8 a.m. and was lowest at 2 p.m.
• Men with normal testosterone showed a significant 15% decline from 8 a.m. to 2 p.m. (p=0.0003).
• Men with low testosterone exhibited a non-significant 4% decline (p=0.54) and failed to demonstrate significant diurnal variation.

Conclusions:

• Men with testosterone deficiency do not exhibit diurnal variation in serum testosterone levels.
• The loss of circadian rhythm in testosterone may be linked to central mechanisms involved in secondary testosterone deficiency pathophysiology.