The 2D:4D digit ratio as biomarker for substance abuse

Purpose: The second (2D, index finger) to fourth (4D, ring finger) digit ratio is a biomarker for prenatal testosterone and estrogen exposure. It has been hypothesized that the developmental origins of health and behavior are modulated by the presence or absence of prenatal sex hormones. Several studies have shown a significant relationship between prenatal testosterone concentrations in amniotic fluid and adult risk taking behavior [1]. As the 2D:4D digit ratio does not change after the age of 2, it may be useful as screening tool for later life substance abuse [2]. The purpose of the current study was to investigate the 2D:4D digit ratio and its potential relationship with drug use and smoking. Methods: A survey was held among N= 1067 Dutch adults (57.6% men), aged 16-55 years old (mean age 23.8 years old). For both hands, digit lengths of the second (2D, index finger) and fourth (4D, ring finger) finger were measured using digital vernier calipers recording to 0.01 mm. Measurements were made from the mid-point of the finger crease proximal to the palm to the tip of the finger. Demographics, smoking status (yes/no) and daily number of cigarettes smoked were recorded. Past year's drug use was rated as (1) never, (2) seldom (1-2 times), (3) now and then (3-11 times), monthly, weekly, or daily. Non-parametric correlations were computed to examine the relationship of the 2D:4D digit ratio with alcohol, drug use, and smoking. In addition, substance use of subjects with a hawk-type (2D:4D 1) were compared. Results: Overall, the left 2D:4D digit ratio correlated significantly with frequency of drug use (r = -0.095, p = 0.003). The right 2D:4D digit ratio correlated significantly with the number of cigarettes smoked (r = -0.092, p = 0.005) and the frequency of drug use (r = -0.125, p = 0.0001). For men, the left 2D:4D digit ratio correlated significantly with frequency of drug use (r = -0.125, p = 0.003). The right 2D:4D digit ratio in men correlated significantly with the number of cigarettes smoked (r = -0.127, p = 0.003) and the frequency of drug use (r = -0.141, p = 0.001). For women, none of the correlations between substance abuse and digit ratio were significant. Subjects with a right 2D:4D1. They also significantly more often were drug users (p = 0.004, 33.6% of hawks versus 24.3% of doves). Conclusion: Subjects with a 2D:4D1. Although the strength of the associations is modest, subjects with a lower 2D:4D digit ratio tend to smoke more cigarettes and use drugs of abuse more frequently