Relative digit length is associated with cognitive abilities in women and men: Epidemiology / Risk and protective factors in MCI and dementia.

Background: Relative length of the index (second digit; 2D) and ring (fourth digit; 4D) fingers on the right hand (2D:4D) is taken to indicate prenatal hormone levels. Lower 2D:4D (i.e., 4D relatively longer) represents more androgen exposure, with men showing lower 2D:4D on average than women. Women from opposite sex twin pairs have lower 2D:4D compared to women from same sex dizygotic twin pairs. Lower 2D:4D correlates with higher scores on spatial and numerical tasks, while higher 2D:4D advantages verbal tasks. Findings, however, have been quite inconsistent. Method: We analyzed cognitive scores in a nationally representative internet panel who were asked whether their index or ring finger was longer (or whether they were the same). N=3525 (1521 men; 2004 women), aged 17 – 108, reported a difference in digit length on their right hands. Cognitive tests included IRT‐scored Number Series (NS), Picture Vocabulary (PV), and Verbal Analogies (VA), plus Serial Sevens (SS)–frequently part of mental status testing. Result: More men (67%) than women (44%) reported relatively longer 4D, consistent with established findings. There were significant interactions by gender, digit length, and age/birthyear on all outcomes. Men outscored women on NS, PV, and VA, and reported higher educational attainment than women. Within women, those with relatively longer 2D reported higher education attainment and scored higher on VA compared to those with relatively longer 4D. However, there was a significant interaction between digit length and age/birthyear for both PV (p=.03) and VA (p=.005): women born more recently had longer 2D associated with higher scores, but older women had longer 4D associated with higher scores, with the crossover around age 65. Within men, those with relatively longer 4D scored higher on NS (p=.0003) and SS (p=.005) than men with relatively longer 2D. Findings were robust to including education as a covariate. Conclusion: Findings add to evidence that sex differences in cognitive abilities in adult women and men may be influenced by differences in prenatal levels of sex steroid hormones, indirectly inferred from relative digit length. Results further suggest that prenatal testosterone exposure may confer an advantage in older women. Grant No. RF1 AG058068. [ABSTRACT FROM AUTHOR]