In a seemingly odd study, researchers looked at index or 2nd and ring or 4th finger (digit) length in 9,044 women enrolled in the Melbourne Collaborative Cohort Study to determine if there was an association between digit length and breast cancer. Specifically, the authors measured the ratio of the lengths of the index and ring fingers (2D:4D ratio) in both hands and the difference between the right and left hand index to ring finger ratios (ΔR minus L hand ratio). The authors then compared these calculations to breast cancer risk, age at menarche (onset of menstruation), and age at menopause. The authors found that both a higher left hand 2D:4D ratio and a lower (ΔR minus L hand) ratio were associated with a higher risk of breast cancer. Increasing right hand 2D:4D ratios and (ΔR minus L hand) ratios were associated with an earlier onset of breast cancer and earlier age of menopause. While the length of index and ring fingers may seem like an unusual measurement to study in breast cancer, there is a scientific basis for these findings. Prior studies have found that both the index and ring finger growth is affected by exposure to androgens like testosterone and to estrogens in a fetus which can affect breast tissue characteristics. Regarding the numbers, men on average have a 2D:4D ratio of 0.947 and women have a ratio of 0.965. A long index finger generally results in an index/ring finger (2D:4D ratio) greater than 1. Others have found statistical associations between high finger length (index/ring finger) ratios and an increased risk of heart disease, obesity, depression, schizophrenia, aggressiveness, assertiveness, leadership and a decreased risk of prostate cancer, autism spectrum disorders, eating disorders, and alcohol dependency. For readers who already have their rulers out, you measure finger length using the palm of the hand. Finger length is the distance from the first crease at the base of the finger to the tip of the finger.
