Callie Barnwell Gibson, PhD (Andrologist/Jr. Embryologist)
Sperm quality can be affected by a variety of factors. Obesity, smoking, alcohol, drug use, frequency of sexual intercourse, and leading a sedentary life style are factors that are known to decrease sperm percent motility, as well as sperm morphology. Sperm quality can also be affected by age and environmental hazards.
Previous research investigating seasonal sperm variation in humans produced mixed results; some studies found seasonal variations while others did not. A study published in 2013 (Levitas et al., 2013)1 compared sperm parameters of over 6,000 semen samples collected between 2006-2009. Specimens were categorized as either normal concentration (sperm concentration ≥20 million/mL) or low sperm concentration (between 4-19.99 million/mL) and the two groups were analyzed separately. Patients undergoing hormonal treatment, or with sperm concentrations less than 4 million/mL were excluded from the study.
As sperm production takes approximately 70 days in men, researchers analyzed the data based on both the season in which the specimen was collected, and the season 70 days prior to the specimen collection day. The semen parameters measured in the study included semen volume, sperm concentration, and percentage of total motility, as well as sperm morphology. Data were adjusted for patient age and abstinence duration prior to the specimen collection.
Researchers did not find an effect of season on semen volume, which remained constant throughout the year, for either the normal concentration or low concentration groups. However, among the patients with normal concentration, the data showed a season-related pattern for all of the other sperm parameters studied. Average sperm concentration peaked during the spring months, and gradually decreased in the fall. Average sperm concentration then recovered in the winter months. Average normal sperm morphology also peaked in the colder months and decreased in the hotter seasons. The mean percentage of fast-motility sperm was lowest in the summer and highest in the winter.
There were no statistically significant differences in percent normal morphology, percent fast-motility, and average sperm concentration between seasons for the low concentration specimens.
Overall, the data from this study showed a seasonal pattern of lower sperm quality during the summer months, with a gradual improvement in the fall through the winter months. Perhaps this is due to the higher temperatures in the semen.
Researchers also examined the Birth Registry at the Soroka University Medical Center from 2005-2010. The highest number of deliveries occurred in the Fall (corresponding to a higher rate of conception the previous Winter), while birth rate was lowest in the Spring (corresponding to conception in the Summer).
Taken together, the data supports a seasonal pattern of sperm quality and rates of human conception. Researchers concluded that men with normal sperm may perform better in the winter.
1Levitas E, Lunenfeld E, Weisz N, et al. Seasonal variations of human sperm cells among 6455 semen samples: a plausible explanation of a seasonal birth pattern. Am J Obstet Gynecol 2013; 208:406, e1-6.