Circannual cycle in plasma testosterone levels in man

Area of Science:

• Endocrinology
• Human Physiology
• Chronobiology

Background:

• Testosterone is a key androgen hormone influencing male health.
• Seasonal variations in hormones are observed in various species.
• Understanding human testosterone seasonality is crucial for health management.

Purpose of the Study:

• To investigate the presence and pattern of circannual variation in plasma testosterone levels in healthy males.
• To identify the timing of peak and nadir testosterone concentrations throughout the year.

Main Methods:

• Blood samples were collected from 15 healthy adult males at 3-month intervals over a year.
• Plasma testosterone levels were quantified using established laboratory assays.
• Statistical analysis was performed to assess the significance of observed seasonal patterns.

Main Results:

• A statistically significant circannual rhythm in plasma testosterone levels was identified.
• Testosterone levels peaked during the summer and early autumn months.
• The lowest testosterone levels (nadir) were observed in winter and early spring.

Conclusions:

• Healthy adult males exhibit a distinct seasonal pattern in testosterone production.
• Testosterone levels naturally fluctuate throughout the year, with a summer/autumn peak and a winter/spring low.
• These findings contribute to understanding the endocrinology of human seasonal rhythms.