The researchers at Washington University School of Medicine in St. Louis and Saint Louis University School of Medicine, US analysed the cases of 723 men who tested positive for COVID-19, mostly in 2020 before vaccines were available.
The data indicate that low testosterone is an independent risk factor for COVID-19 hospitalisation, similar to diabetes, heart disease and chronic lung disease.
The study, published in the journal JAMA Network Open, found that men with low testosterone who developed COVID-19 were 2.4 times more likely to require hospitalisation than those with hormone levels in the normal range.
The researchers also found that men who were once diagnosed with low testosterone but successfully treated with hormone replacement therapy were no more likely to be hospitalised for COVID-19 than those whose hormone levels had always tested in the normal range.
The study suggests that treating men with low testosterone may help protect them against severe disease and reduce the burden on hospitals during COVID-19 waves.
"It is very likely that COVID-19 is here to stay," said study co-senior author Abhinav Diwan, a professor of medicine at Washington University.
"Hospitalisations with COVID-19 are still a problem and will continue to be a problem because the virus keeps evolving new variants that escape immunisation-based immunity," Diwan said.
The researchers noted that low testosterone is very common, found in up to a third of men over 30.
"Our study draws attention to this important risk factor and the need to address it as a strategy to lower hospitalisations," Diwan said.
Diwan and co-senior author Sandeep Dhindsa, an endocrinologist at Saint Louis University, previously had shown that men hospitalised with COVID-19 have abnormally low testosterone levels.
However, severe illness or traumatic injury can cause hormone levels to drop temporarily, they added.