Exploring geographical variations in sperm quality in the continental US

A study published in The World Journal of Men’s Health provides an up-to-date report on the geographical differences in sperm parameters among a group of men residing in six regions of continental US.

Background

Infertility is a leading disability affecting about 8 – 12% of couples worldwide. Among infertility cases, approximately 40% are associated with male factor infertility. Semen analyses, including sperm count, concentration, motility, and morphology, are considered the best indicators of male fertility status. 

Sperm quality can be affected by several factors, including age, body mass index, smoking and drinking habits, physical activity level, educational background, stress, and certain medical conditions. Moreover, there is evidence suggesting that the geographical location of an individual can influence his sperm quality.

The correlation between geographical location and sperm quality has been studied extensively in many countries outside the USA. However, large-scale epidemiological studies on male fertility are absent in continental US.

In the current study, scientists have determined geographical differences in sperm quality among a group of men residing in six different regions of continental US, including Northeast, Southeast, Midwest, West, Pacific, and Southwest. 

Study design

The study was conducted on 5,822 men who self-requested semen analysis between 2019 and 2021. None of the participants had a self-reported history of male factor infertility. Depending of the geographical location, the participants were categorized into six groups, including Northeast, Southeast, Midwest, West, Pacific, and Southwest. 

Semen samples were collected from the participants using a validated at-home mail-in semen collection kit. The participants were instructed to self-collect semen samples using the kit delivered to their home. Afterward, the samples were shipped overnight to the laboratory for semen analysis, which included sperm count, motility, and morphology.

Important observations

The comparative analyses conducted in the study revealed that the average sperm concentration, total number of motile sperm, and total motility were lower in participants from the West region than in participants from other studied locations. A reduction in total sperm count and progressive motility was also observed in participants from the Southwest region.

Participants from the Midwest region exhibited higher total motile sperm count and total sperm motility. Similarly, participants from the Northeast region showed higher average sperm concentration and total sperm count.  

The comparison of semen parameters between the participants aged below and above the age of 35 years revealed variations in sperm concentration, total sperm count, total motile sperm, and total and progressive motility. These differences between younger and older participants were significant in the Northeast and Pacific regions but not the Midwest region.

A total of 1,654 participants were identified to have low sperm count (oligozoospermia) in the study population. Of them, about 50% were aged below 35 years. Notably, no significant difference in the prevalence of oligozoospermia was observed between younger and older participants, irrespective of geographical locations. However, a relatively higher prevalence of oligozoospermia was observed in participants from the Southwest and Southeast regions.

The multivariable analysis conducted in the study revealed that the geographical differences in sperm quality among participants are not affected by their age and body mass index.

Study significance

The study provides a thorough overview on the impact of geographical locations on sperm quality of men residing in six different locations of continental US. According to the study findings, people from the Midwest and Northeast regions have higher sperm quality than those from the Southwest and West regions.

As mentioned by the scientists in the article,

this study will pave the way into a deeper discussion of the interplay between geography, social determinants of fertility care and semen quality.” 

Written by

Dr. Sanchari Sinha Dutta

Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.