But a team of researchers from the Hebrew University-Hadassah Braun School of Public Health and Community Medicine and New York's Icahn School of Medicine wanted to shed some insights regarding this controversial issue. "We are all exposed to many new chemicals, and we have evidence that some of these chemicals, like phthalates, disrupt development of the male reproductive system in utero as well as harm sperm production in adult life", he says, adding that smoking is also toxic for men's sperm counts.
FMI: The study was published online in the journal Human Reproduction Update, where it can be read in full. He is anxious that the style of life, the chemicals we are exposed to and the whole environment has to do with this issue.
But Dr. Levine found a decrease in both sperm concentration and sperm count by more than 50%, indicating that the rate at which decreases is continuous.
Dr. Levine, an epidemiologist, told media that if the trend continued humans would become extinct.
Researchers studied data from 185 studies, which collectively used data from 43,000 male respondents who provided sperm samples from 1971 to 2001.
"Eventually we may have a problem, and with reproduction in general, and it may be the extinction of the human species". Similarly, the average total sperm count fell 1.6 percent annually, with an overall 59 percent decline by the end of the aforementioned period.
In contrast, no significant decline was seen in South America, Asia, and Africa, but the researchers point out that far fewer studies have been conducted on these continents.
The study did not investigate the causes of sperm concentration and total sperm count decline.
Previous research has found that low sperm count is associated with poorer health and an increased risk - albeit, a small one - of dying prematurely. "Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed", the study's authors write. In addition, the meta-analysis looked only at sperm count and concentration, and not at sperm quality, which also affects fertility. Hence, confirming the decline of sperm counts could be quite tricky, especially without the administration of strict standard control of counting methods.
The analysis did not explore reasons for the decline, but researchers said falling sperm counts have previously been linked to various factors such as exposure to certain chemicals and pesticides, smoking, stress, and obesity.