Relationship between the 2D:4D and prenatal testosterone, adult level testosterone, and testosterone change: Meta-analysis of 54 studies.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of observational studies
PubMed 37795916 · doi:10.1002/ajpa.24852
What was done
Meta-analysis of 54 studies comprising 8,077 participants assessing whether hand digit ratio (2D:4D) relates to adult baseline testosterone (44 studies), acute testosterone changes during challenge (6 studies), or prenatal testosterone exposure (10 studies). The authors also tested moderator effects including hand laterality (left vs. right), sex (male vs. female), measurement medium (blood vs. saliva), and prenatal sample type (amniotic fluid vs. cord blood).
What was found
No overall relationship was found between 2D:4D digit ratio and adult testosterone levels, acute testosterone changes, or prenatal testosterone. Secondary analyses also showed no associations across right or left hands, males or females, or blood versus saliva assays. Some evidence indicated a possible relationship specifically with prenatal testosterone measured in amniotic fluid, but not in cord blood. The abstract reported no numerical effect sizes or confidence intervals.
Why it matters
This review directly questions the widespread use of 2D:4D digit ratios as a non-invasive proxy for adult circulating testosterone or prenatal androgen exposure in biological and behavioral research.
Limits
The abstract reports no exact effect sizes, standard errors, or heterogeneity statistics. Sample sizes for acute testosterone reactivity (6 studies) and prenatal testosterone (10 studies) remain relatively small compared to adult baseline measures, and the potential association in amniotic fluid requires dedicated validation.