Current guidelines from the World Health Organization (WHO) typically recommend between 2 and 7 days of abstinence before semen collection or undergoing assisted reproduction techniques. However, a new study led by researchers at the University of Oxford suggests that regular ejaculation—whether through sexual activity or masturbation—results in higher quality sperm, with less DNA damage.
The findings are based on a broad cross-species analysis revealing a common pattern in many animals, from insects to mammals. Stored sperm (whether in males or females) deteriorates rapidly, leading to reduced sperm performance, fertilization success, and embryo quality. It is crucial to note that the new study also provides insights into why this occurs.
Researchers conducted a meta-analysis of 115 studies in humans (involving 54,889 men) and 56 studies in 30 non-human species. This confirmed that stored mature sperm tends to deteriorate in quality regardless of the male's age, a process known as postmeiotic sperm senescence.
In humans, longer periods of sexual abstinence were associated with increased sperm DNA damage and oxidative stress, along with reduced sperm motility and viability.
Co-lead author Rebecca Dean from the Department of Biology, University of Oxford, stated: "Given that sperm are highly motile and have minimal cytoplasm, they quickly deplete their stored energy reserves and have limited repair capacity. This makes storage particularly detrimental compared to other cell types. Our study highlights how regular ejaculation can provide a small but significant boost to male fertility."
Differences between men and women
Both male and female animals can store sperm as a reproductive strategy (in humans, sperm can last several days in women, but the effects of such storage are unknown). In males, this ensures enough sperm for mating, while in females, it can allow reproduction even when males are scarce. However, the study found a notable difference in sperm deterioration rates between males and females. In the species studied, females tend to be better than males at preserving sperm quality long-term.
"This likely reflects the evolution of specific female adaptations, such as specialized storage organs that provide antioxidants to prolong sperm viability," explained lead author Irem Sepil from the Department of Biology, University of Oxford. "These organs often secrete reproductive fluids to nourish sperm and could offer unexplored avenues for biomimetic technology to enhance artificial sperm storage in the future."
Principal author Krish Sanghvi, a professor at the Department of Biology, University of Oxford, added: "Ejaculations should be considered as populations of individual sperm undergoing birth, death, aging, and selective mortality. The rates of these demographic processes may differ between men and women, mediating the 'demographic' structure of sperm populations and sex-specific differences in the effects of sperm storage."
Implications for human fertility
The fact that sperm can age in both sexes independently of the organism's age has largely been overlooked in reproductive medicine. Therefore, the findings have immediate implications for clinical practice. For example, the current seven-day maximum limit set in WHO guidelines may be too long. This aligns with recent evidence suggesting that ejaculating within 48 hours of semen collection can significantly improve IVF outcomes.
By bridging the gap between biomedical and zoological research, this study offers a new perspective on understanding reproduction. In addition to influencing fertility clinic protocols and assisted reproduction, the findings could also benefit captive breeding programs for endangered species and deepen our understanding of how species developed mechanisms to reduce sperm damage during storage.