Male sperm count has halved over the last 40 years, due to our polluted environment and unhealthy lifestyles — and scientists now worry it could lead to the end of the human race.

Sperm counts in human males across the globe have decreased more than 50% in the last 40 years.

“Eventually, we may have a problem, and with reproduction in general, and it may be the extinction of the human species,” Dr. Hagai Levine, lead researcher of the study told the BBC these numbers are alarming.

Levine did not give an estimated time frame, but said: “If we will not change the ways that we are living and the environment and the chemicals that we are exposed to, I am very worried about what will happen in the future.”

In the study, published in the journal Human Reproduction Update, the international team of researchers analyzed 185 studies from 1973 to 2011 and found that in reports taken from North America, Europe, Australia and New Zealand, there was a 52.4% decrease in overall sperm concentration and a 59.3% decrease in total sperm count. There were, however, no changes in semen volume over the study period.

Researchers studying sperm counts in South America, Asia, and Africa, on the other hand, found no significant decreases in sperm count or concentration, but there were fewer studies to work with.

The swath of studies included over 42,000 male participants and men from 50 different countries. The analysis shows that Western men are more susceptible to lower sperm counts than those from other parts of the world, which researchers believe is related to chemicals in our food and environment.

The study states that there was a high proportion of men with sperm concentration below 40 million/ml, which is considered low fertility. Despite previous studies saying that sperm count was decreasing over time, this was the first study of this scale to confirm that the proportion of men with low fertility and infertility is steadily increasing.

The researchers call this a public health concern, not just for reasons of male fertility, but because reduced sperm count has been a predictor of all-cause mortality and morbidity, and is associated with the deformities of the genitals and testicular cancer, says the study.

The study doesn’t say exactly why this decline is taking place but refer to environmental factors like chemicals, pesticides, heat, diet, smoking, and stress as influences on sperm count.

“This study,” said Dr. Levine, “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.”