A new study has found that exposure to Wi-Fi connections lowers male fertility rates and reduces couples' chances of having children by killing sperm, adding to mounting evidence that electromagnetic waves are harmful.

The Japanese study, done between August and November on 51 men, is reportedly the first such trial that focuses on the effects of electromagnetic waves from Wi-Fi devices such as mobile phones and home routers on sperm motion and death.

Researcher Kumiko Nakata, from the Reproductive Medicine Research Centre at Yamashita Shonan Yume Clinic, noted that electromagnetic waves have been said to be safe for humans, in terms of health and well-being. But her study showed that prolonged exposure to the waves from Wi-Fi devices lowered male fertility.

"Our study has shown that over a relatively short time, a Wi-Fi shield can offer some protection from the harmful effects of the electromagnetic waves," she said. "However, there is mounting evidence that the effects of electromagnetic waves on sperm may be having a significant effect on human reproduction."

The men in the study, whose average age came to 38.4 years, were involved in in-vitro fertilisation or artificial insemination procedures at the clinic in Japan.

Sperm samples were taken from them and split into three groups - one whose samples were not exposed to electromagnetic waves from a Wi-Fi router, one whose sperm were protected by a small shield that intercepted the waves, and one whose sperm were fully exposed to the waves.

Ms Nakata, who specialises in embryology and spermatology, said the sperm samples were placed near a pocket Wi-Fi router, in the way that a mobile phone would be carried in a man's trousers.

The sperm were exposed to electromagnetic waves from the Wi-Fi router for lengths of 30 minutes, 60 minutes, two hours, and 24 hours. Sperm motion was then tested.

While there was little difference in sperm motility rates among the different groups after exposures of 30 minutes and 60 minutes, the study found that the longer the exposure, the lower the sperm motility rate and the higher the death rate.

The World Health Organisation predicts that infertility among both sexes will be the third most serious condition after cancer and cardiovascular diseases in the 21st century.

The study was a collaboration between the Reproductive Medicine Research Centre at Yamashita Shonan Yume Clinic and the Faculty of Life and Environmental Sciences at the University of Yamanashi.