The second to fourth digit (2D:4D) ratios, smoking, and problem drinking in a young adult university student sample

Abstract

BackgroundRelative length of second finger to fourth finger (2D:4D ratio) has been shown to be a putative indirect marker of the amount ofin utero testosterone levels. 2D:4D ratios are claimed to be inversely associated with prenatal testosterone levels. ObjectiveWe aimed to investigate whether 2D:4D ratios are independently associated with smoking and problem drinking in young adults. MethodsWe recruited a convenience sample of 661 university students and used the CAGE questionnaire to identify problem drinking. Smokers were assessed with the Fagerström Test for Nicotine Dependence (FTND). Impulsivity was measured with the Barratt Impulsiveness Scale. Results: 2D:4D ratios were lower in students who were problem drinkers than in those who were non-drinkers or non-problematic drinkers (t=−2.07, p = .039 for right hand; t=−2.02, p = .044 for left hand). 2D:4D ratios were comparable between regular smoker students and non-smoker or irregular smoker students. Problem drinking or regular smoking were not independently associated with 2D:4D ratios in regression analyses. However, 2D:4D ratios on both hands associated negatively with CAGE scores (95% CI: −6.24 to −.64, p = .016 for right hand; 95% CI: −6.68 to −.41, p = .027 for left hand) and positively with FTND scores (95% CI: 1.58–27.06, p = .028 for right hand; 95% CI: 5.06–29.03, p = .006 for left hand) independently of the effects of age, sex, and impulsivity. ConclusionPrenatal testosterone levels, as indirectly assessed by 2D:4D ratios, are independently associated with the severity of alcohol abuse and nicotine dependence when other factors such as sex, age, and impulsivity are considered.