Second to fourth digit ratio (2D:4D) and testosterone in men

Area of Science:

• Endocrinology
• Human Reproduction
• Biometrics

Background:

• The 2D:4D digit ratio (second digit to fourth digit length) is a proposed marker of prenatal androgen exposure.
• Testosterone plays a crucial role in male reproductive development and function.
• Understanding the relationship between digit ratio and testosterone is important for reproductive health research.

Purpose of the Study:

• To examine the association between the 2D:4D digit ratio and adult testosterone levels.
• To compare these associations in men attending an infertility clinic versus men from the general population.

Main Methods:

• Collected 2D:4D digit ratio and testosterone data from two distinct male cohorts.
• Sample 1: 43 men attending an infertility clinic.
• Sample 2: 51 men from the general population.

Main Results:

• In the infertility clinic sample, negative associations were found between 2D:4D and testicular function.
• Men with a lower right-hand 2D:4D compared to their left hand had higher testosterone levels.
• No significant associations between 2D:4D or its side differences and testosterone were observed in the general population sample.

Conclusions:

• Adult testosterone levels may correlate with 2D:4D in men with impaired testicular function, but not in normative samples.
• The observed associations between 2D:4D and fertility traits likely stem from early organizational effects of testosterone.
• This suggests prenatal testosterone exposure, rather than current activational effects, influences these relationships.