Doctors in the central Chinese city of Wuhan plan to embark on a long-term study of the effects of the coronavirus on the male reproductive system, building on small-scale research indicating that the pathogen could affect sex hormone levels in men. Though still preliminary and not peer reviewed, the study is the first clinical observation of the potential impact of Covid-19, the disease caused by the coronavirus, on the male reproductive system, especially among younger groups. In a paper published on the preprint research platform medRxiv.org , the researchers – from Zhongnan Hospital of Wuhan University and the Hubei Clinical Research Centre for Prenatal Diagnosis and Birth Health – said they analysed blood samples from 81 men aged 20 to 54 who tested positive for the coronavirus and were hospitalised in January. The median age of the participants was 38 and roughly 90 per cent of them had only mild symptoms. The samples were collected in the last days of their stay in hospital. Using the samples, the team looked at the ratio of testosterone to luteinising hormone (T/LH). A low T/LH ratio can be a sign of hypogonadism, which in men is a malfunction of the testicles that could lead to lower sex hormone production. The average ratio for the Covid-19 patients was 0.74, about half the normal level. Testosterone is the main male sex hormone critical for the development of primary and secondary sexual characteristics including testes, muscle, bone mass and body hair. Luteinising hormone is found in both men and women, and best known for its ability to trigger ovulation. Common symptoms of hypogonadism in men include abnormally large breasts and erectile dysfunction. The condition can be cured. Erectile disorders caused by a T/LH ratio lower than 0.87 can be relieved effectively by testosterone treatment, according to a study in peer-reviewed journal Archives of Sexual Behaviour in 1997. “Since more than half of the people with Covid-19 were reproductive-aged, more attention should be paid to the effect of Sars-CoV-2 on the reproductive system,” the Wuhan researchers said in their paper, referring to the official name for the new coronavirus. They said their results were not conclusive and the blood samples were not direct proof of reproductive problems with Covid-19 patients. Other factors, such as medication and immune system response, could also cause changes in hormones. Will the coronavirus kill off the ‘dinosaur’ world of academic publishing? The researchers said they planned to launch a long-term study, which might include the collection and analysis of sperm samples and interviews with coronavirus patients. Previous studies have indicated that the new coronavirus could bind with ACE2, a receptor protein cell, a large number of which are concentrated in the testicles. Li Yufeng, a professor of reproductive medicine at Tongji Hospital in Wuhan, had predicted in a study that the testicles could become a major target of the coronavirus attack. Other studies have also suggested that severe acute respiratory syndrome, or Sars, a distant relative of the new coronavirus, could also cause inflammation in the testicles. A researcher with the State Key Laboratory of Reproductive Medicine at Nanjing Medical University, said the new observations were “highly valuable information” but a bigger sample would be needed to clarify the results. “Many viruses can affect fertility, but not every virus can cause a pandemic. If the impact is long lasting, it can be a problem,” the researcher said, declining to be named because of the sensitivity of the issue. Purchase the China AI Report 2020 brought to you by SCMP Research and enjoy a 20% discount (original price US$400). This 60-page all new intelligence report gives you first-hand insights and analysis into the latest industry developments and intelligence about China AI. Get exclusive access to our webinars for continuous learning, and interact with China AI executives in live Q&A. Offer valid until 31 March 2020.