Digit ratios and hospitalization for COVID-19: A test of the low-androgen-driven and high-androgen-driven theories of COVID-19 severity

Background Sex hormones are likely to be important determinants of COVID-19 severity, and two opposing explanations regarding severity, the low-androgen-driven and high-androgen-driven theories, seek to explain this pattern. Digit ratios are sex dependent (males < females) and are claimed to be markers for both prenatal and postnatal testosterone. Objectives Here, we use a measure of COVID-19severity (hospitalization), compare digit ratios in patients and controls and consider whether vaccination status changed these associations. Material and methods Four digits were measured (2D, 3D, 4D, 5D). There were 194 participants (94 hospitalized patients [45 men] and 100 controls [53 men]) in Sample I and 162 participants (100 hospitalized [42 men], including 40 vaccinated and 62 controls [32 men]) in Sample II. Six ratios were calculated (2D:3D; 2D:4D; 2D:5D; 3D:4D; 3D:5D, 4D:5D) and compared between COVID-19 hospitalized and non-hospitalized patients and vaccinated and non-vaccinated. Results In comparison to controls, we found higher ("feminized") means in patient ratios that included 5D (2D:5D; 3D:5D; 4D:5D) in both samples. The differences were independent of sex and age. Hospitalized patients with COVID-19 have higher (feminized) means and higher standard deviations (SDs) for 5D digit ratios. Discussion Digit ratios are sex dependent (males < females) and are considered as markers for both prenatal and postnatal testosterone. If verified in future studies, the results will be helpful in regard to targeting mortality-reducing therapies for COVID-19 in certain groups of patients. Conclusion We conclude that the association between high (feminized) 5D ratios and hospitalization supports the low-androgen-driven theory of COVID-19 severity.