Researchers at Israel’s Ben-Gurion University of the Negev found that sperm concentration and the percentage of fast motility—the ability to move spontaneously and independently—decreased significantly from spring into summer and fall, rebounding in the winter.
The physical structure of the sperm cells was also the healthiest in the winter months, according to the study, which tested 6,455 semen samples over the course of three years.
“This study was aimed to explore the possibility that changing weather is somehow related to the quality of sperm, a phenomenon well known from the animal world,” study leader Eliahu Levitas said in an email.
Pears in Window, Moscow
Photograph by Sam Abell, National Geographic