ISSN : 2146-3123
E-ISSN : 2146-3131

The Relationship Between Digit Ratio and Circadian Typology Among Medical Students
Çağla İşman 1, Şebnem Gülen 1, Nimet Gündoğan 1
1Department of Physiology, Medical Faculty of Başkent University, Ankara
Pages : 68-73


Objectives: Morningness-eveningness preference stands for interindividual chronobiological differences. This study was designed to investigate if prenatal testosterone exposure is a candidate for having a causal role in sexual dimorphism observed in circadian typology.

Materials and Methods: A total of 183 students (111 females, 72 males; mean age 20.7 years) were involved in the study. Circadian typology was assessed using the Horne-Ostberg Morningness-Eveningness Questionnaire. Digit lenghts were measured with digital calipers and digit ratio (2D/4D) was calculated by dividing the length of the second digit by that of the fourth digit.

Results: Circadian typology assessment revealed 54 morning-(29.5%), 100 intermediate-(54.6%) and 29 evening-(15.8%) type students. Digit ratio of both hands in males were significantly lower than females (p<0.001). Digit ratio for both hands in morningness trait were significantly higher than intermediate (p<0.001) and eveningness (p<0.05 for the left and p<0.01 for the right hand) traits. Morning type was more common among females (35.1% vs 20.8%; p<0.05). Higher digit ratio was significantly associated with the morning type for both of the hands in both genders.

Conclusion: Prenatal testosterone exposure, represented by digit ratio (2D/4D) as a proxy marker, seems to have a causal role in sexual dimorphism observed in the circadian typology preferences.

Keywords : Circadian typology; gender; digit ratio; fetal testosterone
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