Ma J, et al. - Researchers investigated the link between abnormal BMI and semen quality in this observational study on 3,966 sperm donors from a large sperm bank in Wuhan city, China. They specifically intended to gain insight into the link between underweight and semen quality. These participants passed the screening for sperm donation and underwent 29,949 semen examinations between 1 January 2013 and 9 April 2018. Dose–response analyses were carried out using linear mixed models. A 3.0% and 7.4% reduction in sperm concentration, total sperm number and total motile sperm count, respectively, was seen in significant relation to underweight. A significant association of overweight with a 4.2%, 3.9% and 3.6% reduction in semen volume, total sperm number and total motile sperm count, respectively, was also observed. Overall, both underweight and overweight were related to lower semen quality and therefore, it is important to maintain a normal weight for men.