Posted on 27 May 2020
Of course, no one is suggesting that having a short ring finger causes an increase in the risk of dying from COVID-19. Rather, ring finger length is thought to be linked to testosterone exposure in the womb, which has been proposed as a potential risk factor for COVID-19 in men.
The study, published in the journal Early Human Development, looked at existing data on the digit ratios (index finger length divided by ring finger length) for 103,482 men and 83,366 women across 41 countries. They found that among males, a higher digit ratio (suggesting low prenatal testosterone) was associated with increased risk of severe/fatal COVID-19 symptoms.
This is an intriguing finding, given that higher testosterone negatively impacts the immune system. One possible explanation is that higher testosterone is associated with higher expression of the ACE2 receptor. The Sars-Cov-2 attaches itself to ACE2 receptors in order to gain access to human cells using the its Spike protein. Paradoxically, increased expression of ACE2 seems to be associated with reduced susceptibility to COVID-19 infection.
More research will be needed before a definitive link between testosterone and COVID susceptibility can be confirmed, however. Until then, we probably should not be basing our social distancing practices on finger length!
Understanding COVID-19: Digit ratio (2D:4D) and sex differences in national case fatality rates: https://doi.org/10.1016/j.earlhumdev.2020.105074
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