The first systematic review and meta-analysis of trends in sperm count reports a significant decline in sperm concentration and total sperm count among men from Western countries. The study is published today in Human Reproduction Update, the leading journal in the fields of Reproductive Biology and Obstetrics and Gynecology.
By screening 7,500 studies and conducting a meta-regression analysis on 185 studies between 1973 and 2011, the researchers found a 52.4 percent decline in sperm concentration, and a 59.3 percent decline in total sperm count, among men from North America, Europe, Australia and New Zealand who were not selected based on their fertility status. In contrast, no significant decline was seen in South America, Asia and Africa, where far fewer studies have been conducted.
The study also indicates the rate of decline among Western men is not decreasing: the slope was steep and significant even when analysis was restricted to studies with sample collection between 1996 and 2011.
No significant decline has been seen in South America, Asia and Africa, but the researchers point out that far fewer studies have been conducted on these continents. However, Dr Levine is concerned that eventually sperm counts could fall in these places too.
“Given the importance of sperm counts for male fertility and human health, this study is an urgent wake-up call for researchers and health authorities around the world to investigate the causes of the sharp ongoing drop in sperm count, with the goal of prevention,” said Dr. Hagai Levine, the lead author and Head of the Environmental Health Track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine, in the Hebrew University of Jerusalem’s Faculty of Medicine.
There is no clear evidence for the reason for this apparent decrease. But it has been linked with exposure to chemicals used in pesticides and plastics, obesity, smoking, stress, diet, and even watching too much TV.
Dr Levine says that there is an urgent need to find out why sperm counts are decreasing and to find ways of reversing the trend.
“We must take action – for example, better regulation of man-made chemicals – and we must continue our efforts on tackling smoking and obesity.
Defining a person’s sperm count is a complex process. There are a number of measurements that are considered in semen analysis. First, a physician will look at the concentration — how many sperm there are per cc or milliliter of semen (the fluid). Next, we need to know how many cc of semen are present. So a count of 40 million sperm per cc with only 1cc of fluid may not be as good as a count with 18 million and 4cc. We like to see more than 20 million sperm per cc and 2-5cc of semen. Another measurement to consider is what percentage of the sperm is moving forward progressively; 50 percent motility is considered normal. The next factor is sperm morphology which determines what percentage of sperm look normal. When you assess the fertilizing potential of a given specimen, you must consider all these factors. Thus, a slight abnormality in sperm count may be compensated for by better motility or an increase in volume.