Humans could become extinct if sperm counts in men continue to fall at current rates, a doctor has warned.
Researchers assessing the results of nearly 200 studies say sperm counts among men from North America, Europe, Australia, and New Zealand, seem to have halved in less than 40 years.
Some experts are sceptical of the Human Reproduction Update findings.
But lead researcher Dr Hagai Levine said he was “very worried” about what might happen in the future.
The assessment, one of the largest ever undertaken, brings together the results of 185 studies between 1973 and 2011.
Dr Levine, an epidemiologist, told the BBC that if the trend continued humans would become extinct!
Smoking and obesity
The new study has reduced the possibility of errors it does not entirely remove them. So, he says, the results should be treated with caution.
“The debate has not yet been resolved and there is clearly much work still to be done.
“However, the paper does represent a step forward in the clarity of the data which might ultimately allow us to define better studies to examine this issue.”
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.”