Sperm motility, a measure of sperm quality, is declining in the USA and Spain, two new studies have found.
Previous analyses have found an overall falling sperm count in the past 50 years, but this latest research shows that sperm cell swimming ability is also on the decline. Sperm motility is one of the key traits that boost a sperm cell's chances of reaching and fertilising an egg.
'Male infertility is under-recognised and these results are a cause for concern,' said Dr James Hotaling, a urologist and study author at the Reproductive Medical Associates of New Jersey (RMANJ).
In the first study, researchers from the RMANJ, and the Instituto Valenciano Infertilidad in Valencia, Spain, analysed changes in total motile sperm count of 119,972 men who were seeking fertility treatment between 2002 and 2017.
Over the 15-year period, the percentage of patients with a high motile sperm count dropped from 84.7 percent to 79.1 percent. The percentage of males with a low motile sperm count rose from 8.9 percent to 11.6 percent.
The motile sperm count of men in the highest group decreased by 1.8 percent each year of the study, the researchers found. However, this could partly be accounted for because motile sperm count decreased by 1.1 percent each year as men got older.
Finding similar results in both the USA and Spain, the researchers emphasised the international nature of the problem.
'We did not expect to see the same fall in sperm quality in Spain and the US but whatever we did in the study it didn't go away,' Dr Hotaling told the Times.
Although the study did not identify the causes of the trend, lifestyle and environmental factors are expected to be playing a significant role, said study author Dr Ashley Tiegs of RMANJ.
'[Our study] supports a lot of the other literature that shows environmental factors like plastics and smoking and obesity are big ones,' Dr Tiegs told Mail Online. 'We know obesity is on the rise and it does affect sperm quality. It increases the risk of morbidity and mortality, but it can also affect offspring too.'
In the second study, researchers from Icahn School of Medicine at Mount Sinai in New York and Reproductive Medical Associates of New York collected 124,107 specimens from donors in six cities across the USA between 2007 and 2017. Unlike in the previous study, these were men who had not reported any problems with their fertility.
Measuring total sperm count, sperm concentration and motile sperm count, the researchers observed a decline in sperm quality in all regions studied, with the exception of New York, where donors' sperm quality remained constant.
'The trend toward lower sperm counts in this study is concerning,' said Dr Peter Schlegel, president-elect of the American Society for Reproductive Medicine (ASRM). 'Whether the causes underlying it are environmental or lifestyle-related, they will be difficult to parse out. Pollution, endocrine disrupting chemicals, poor exercise habits and convenient, yet nutritionally poor, dietary choices could all play a part.'
The research was presented at the ASRM's annual conference.